String.LastIndexOf 方法

定義

報告這個執行個體中指定之 Unicode 字元或字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified Unicode character or string within this instance. 如果在此執行個體中找不到該字元或字串,此方法會傳回 -1。The method returns -1 if the character or string is not found in this instance.

多載

LastIndexOf(String, Int32, StringComparison)

報告目前 String 物件中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index of the last occurrence of a specified string within the current String object. 搜尋會從指定的字元位置開始,然後反向朝字串的開頭進行。The search starts at a specified character position and proceeds backward toward the beginning of the string. 參數會指定搜尋指定字串時要執行的比較類型。A parameter specifies the type of comparison to perform when searching for the specified string.

LastIndexOf(String, Int32, Int32)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串開頭指定數目的字元位置進行。The search starts at a specified character position and proceeds backward toward the beginning of the string for a specified number of character positions.

LastIndexOf(Char, Int32, Int32)

報告這個執行個體的子字串中,指定的 Unicode 字元最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of the specified Unicode character in a substring within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串開頭指定數目的字元位置進行。The search starts at a specified character position and proceeds backward toward the beginning of the string for a specified number of character positions.

LastIndexOf(String, StringComparison)

報告目前 String 物件中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index of the last occurrence of a specified string within the current String object. 參數會指定要用於指定字串的搜尋類型。A parameter specifies the type of search to use for the specified string.

LastIndexOf(Char)

報告這個執行個體中指定之 Unicode 字元最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified Unicode character within this instance.

LastIndexOf(Char, Int32)

報告這個執行個體中指定之 Unicode 字元最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified Unicode character within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串的開頭進行。The search starts at a specified character position and proceeds backward toward the beginning of the string.

LastIndexOf(String)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance.

LastIndexOf(String, Int32, Int32, StringComparison)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串開頭指定數目的字元位置進行。The search starts at a specified character position and proceeds backward toward the beginning of the string for the specified number of character positions. 參數會指定搜尋指定字串時要執行的比較類型。A parameter specifies the type of comparison to perform when searching for the specified string.

LastIndexOf(String, Int32)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串的開頭進行。The search starts at a specified character position and proceeds backward toward the beginning of the string.

LastIndexOf(String, Int32, StringComparison)

報告目前 String 物件中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index of the last occurrence of a specified string within the current String object. 搜尋會從指定的字元位置開始,然後反向朝字串的開頭進行。The search starts at a specified character position and proceeds backward toward the beginning of the string. 參數會指定搜尋指定字串時要執行的比較類型。A parameter specifies the type of comparison to perform when searching for the specified string.

public:
 int LastIndexOf(System::String ^ value, int startIndex, StringComparison comparisonType);
public int LastIndexOf (string value, int startIndex, StringComparison comparisonType);
member this.LastIndexOf : string * int * StringComparison -> int
Public Function LastIndexOf (value As String, startIndex As Integer, comparisonType As StringComparison) As Integer

參數

value
String

要搜尋的字串。The string to seek.

startIndex
Int32

搜尋開始位置。The search starting position. 搜尋會從 startIndex 朝這個執行個體的開頭進行。The search proceeds from startIndex toward the beginning of this instance.

comparisonType
StringComparison

其中一個列舉值,指定搜尋規則。One of the enumeration values that specifies the rules for the search.

傳回

Int32

如果找到該字串,則為 value 參數以零為起始的索引位置,如果找不到該字串或者目前的執行個體等於 Empty,則為 -1。The zero-based starting index position of the value parameter if that string is found, or -1 if it is not found or if the current instance equals Empty.

例外狀況

valuenullvalue is null.

目前的執行個體不等於 Empty,且 startIndex 小於零或大於目前執行個體的長度。The current instance does not equal Empty, and startIndex is less than zero or greater than the length of the current instance.

-或--or-

目前的執行個體等於 EmptystartIndex 小於 -1 或大於零。The current instance equals Empty, and startIndex is less than -1 or greater than zero.

comparisonType 不是有效的 StringComparison 值。comparisonType is not a valid StringComparison value.

範例

下列範例示範三個方法的多載 LastIndexOf ,此方法會使用不同的列舉值來尋找另一個字串中的最後一個字串 StringComparisonThe following example demonstrates three overloads of the LastIndexOf method that find the last occurrence of a string within another string using different values of the StringComparison enumeration.

// This code example demonstrates the 
// System.String.LastIndexOf(String, ..., StringComparison) methods.

using System;
using System.Threading;
using System.Globalization;

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the last occurrence of a character using different " + 
                   "values of StringComparison.";
    string resultFmt = "Comparison: {0,-28} Location: {1,3}";

// Define a string to search for.
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    string CapitalAWithRing = "\u00c5"; 

// Define a string to search. 
// The result of combining the characters LATIN SMALL LETTER A and COMBINING 
// RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
// LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
    string cat = "A Cheshire c" + "\u0061\u030a" + "t";
    int loc = 0;
    StringComparison[] scValues = {
        StringComparison.CurrentCulture,
        StringComparison.CurrentCultureIgnoreCase,
        StringComparison.InvariantCulture,
        StringComparison.InvariantCultureIgnoreCase,
        StringComparison.Ordinal,
        StringComparison.OrdinalIgnoreCase };

// Clear the screen and display an introduction.
    Console.Clear();
    Console.WriteLine(intro);

// Display the current culture because culture affects the result. For example, 
// try this code example with the "sv-SE" (Swedish-Sweden) culture.

    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
    Console.WriteLine("The current culture is \"{0}\" - {1}.", 
                       Thread.CurrentThread.CurrentCulture.Name,
                       Thread.CurrentThread.CurrentCulture.DisplayName);

// Display the string to search for and the string to search.
    Console.WriteLine("Search for the string \"{0}\" in the string \"{1}\"", 
                       CapitalAWithRing, cat);
    Console.WriteLine();

// Note that in each of the following searches, we look for 
// LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains 
// LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates 
// the string was not found.
// Search using different values of StringComparsion. Specify the start 
// index and count. 

    Console.WriteLine("Part 1: Start index and count are specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. Specify the 
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }
    }
}

/*
Note: This code example was executed on a console whose user interface 
culture is "en-US" (English-United States).

This code example produces the following results:

Find the last occurrence of a character using different values of StringComparison.
The current culture is "en-US" - English (United States).
Search for the string "Å" in the string "A Cheshire ca°t"

Part 1: Start index and count are specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

Part 2: Start index is specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

Part 3: Neither start index nor count is specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

*/
' This code example demonstrates the 
' System.String.LastIndexOf(String, ..., StringComparison) methods.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the last occurrence of a character using different " & _
                              "values of StringComparison."
        Dim resultFmt As String = "Comparison: {0,-28} Location: {1,3}"
        
        ' Define a string to search for.
        ' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
        Dim CapitalAWithRing As String = "Å"
        
        ' Define a string to search. 
        ' The result of combining the characters LATIN SMALL LETTER A and COMBINING 
        ' RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
        ' LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
        Dim cat As String = "A Cheshire c" & "å" & "t"
        Dim loc As Integer = 0
        Dim scValues As StringComparison() =  { _
                        StringComparison.CurrentCulture, _
                        StringComparison.CurrentCultureIgnoreCase, _
                        StringComparison.InvariantCulture, _
                        StringComparison.InvariantCultureIgnoreCase, _
                        StringComparison.Ordinal, _
                        StringComparison.OrdinalIgnoreCase }
        Dim sc As StringComparison
        
        ' Clear the screen and display an introduction.
        Console.Clear()
        Console.WriteLine(intro)
        
        ' Display the current culture because culture affects the result. For example, 
        ' try this code example with the "sv-SE" (Swedish-Sweden) culture.
        Thread.CurrentThread.CurrentCulture = New CultureInfo("en-US")
        Console.WriteLine("The current culture is ""{0}"" - {1}.", _
                           Thread.CurrentThread.CurrentCulture.Name, _
                           Thread.CurrentThread.CurrentCulture.DisplayName)
        
        ' Display the string to search for and the string to search.
        Console.WriteLine("Search for the string ""{0}"" in the string ""{1}""", _
                           CapitalAWithRing, cat)
        Console.WriteLine()
        
        ' Note that in each of the following searches, we look for 
        ' LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains 
        ' LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates 
        ' the string was not found.
        ' Search using different values of StringComparsion. Specify the start 
        ' index and count. 
        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparsion. Specify the 
        ' start index. 
        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparsion. 
        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
    
    End Sub
End Class

'
'Note: This code example was executed on a console whose user interface 
'culture is "en-US" (English-United States).
'
'This code example produces the following results:
'
'Find the last occurrence of a character using different values of StringComparison.
'The current culture is "en-US" - English (United States).
'Search for the string "Å" in the string "A Cheshire ca°t"
'
'Part 1: Start index and count are specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'
'Part 2: Start index is specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'
'Part 3: Neither start index nor count is specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

搜尋 startIndex 會從字元位置開始,並繼續進行,直到 value 找到任何一個或檢查第一個字元位置為止。The search begins at the startIndex character position and proceeds backward until either value is found or the first character position has been examined. 例如,如果 startIndexLength -1,則方法會搜尋字串中最後一個字元到開頭的每個字元。For example, if startIndex is Length - 1, the method searches every character from the last character in the string to the beginning.

comparisonType參數指定要使用目前或不區分大小寫的文化特性搜尋 value 參數、使用區分大小寫或不區分大小寫的搜尋,以及使用單字或序數比較規則。The comparisonType parameter specifies to search for the value parameter using the current or invariant culture, using a case-sensitive or case-insensitive search, and using word or ordinal comparison rules.

給呼叫者的注意事項

字元集包含可忽略的字元,這些字元在執行語言或區分文化特性的比較時不列入考慮。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 執行區分文化特性的搜尋 (也就是說,如果 comparisonType 不是 OrdinalOrdinalIgnoreCase) 時,如果 value 包含可忽略的字元,則結果等於在已移除該字元的情況下搜尋。In a culture-sensitive search (that is, if comparisonType is not Ordinal or OrdinalIgnoreCase), if value contains an ignorable character, the result is equivalent to searching with that character removed.

在下列範例中, LastIndexOf(String, Int32, StringComparison) 方法是用來找出軟連字號的位置 (U + 00AD) 接著是 "m",以兩個字串中的最後 "m" 開頭。In the following example, the LastIndexOf(String, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m", starting with the final "m" in two strings. 只有其中一個字串包含必要的子字串。Only one of the strings contains the required substring. 如果範例是在 .NET Framework 4 或更新版本上執行,則在這兩種情況下,因為軟連字號是可忽略的字元,所以在執行區分文化特性的比較時,方法會傳回字串中 "m" 的索引。If the example is run on .NET Framework 4 or later, in both cases, because the soft hyphen is an ignorable character, the method returns the index of "m" in the string when it performs a culture-sensitive comparison. 請注意,在第一個字串的案例中,包含軟連字號後接 "m",方法會傳回 "m" 的索引,而非軟連字號的索引。Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method returns the index of the "m" and not the index of the soft hyphen. 只有在執行序數比較時,方法才會傳回第一個字串中選擇性連字號的索引。The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

[!程式碼-csharpsystem.string. LastIndexOf # 25][! code-vbsystem.string. LastIndexOf # 25][!code-csharpSystem.String.LastIndexOf#25] [!code-vbSystem.String.LastIndexOf#25]

適用於

LastIndexOf(String, Int32, Int32)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串開頭指定數目的字元位置進行。The search starts at a specified character position and proceeds backward toward the beginning of the string for a specified number of character positions.

public:
 int LastIndexOf(System::String ^ value, int startIndex, int count);
public int LastIndexOf (string value, int startIndex, int count);
member this.LastIndexOf : string * int * int -> int
Public Function LastIndexOf (value As String, startIndex As Integer, count As Integer) As Integer

參數

value
String

要搜尋的字串。The string to seek.

startIndex
Int32

搜尋開始位置。The search starting position. 搜尋會從 startIndex 朝這個執行個體的開頭進行。The search proceeds from startIndex toward the beginning of this instance.

count
Int32

要檢視的字元位置數目。The number of character positions to examine.

傳回

Int32

如果找到該字串,則為 value 的以零為起始索引位置,如果找不到該字串或者目前的執行個體等於 Empty,則為 -1。The zero-based starting index position of value if that string is found, or -1 if it is not found or if the current instance equals Empty.

例外狀況

valuenullvalue is null.

count 為負。count is negative.

-或--or-

目前的執行個體不等於 Empty,且 startIndex 為負。The current instance does not equal Empty, and startIndex is negative.

-或--or-

目前的執行個體不等於 Empty,且 startIndex 大於這個執行個體的長度。The current instance does not equal Empty, and startIndex is greater than the length of this instance.

-或--or-

目前的執行個體不等於 Empty,且 startIndex - count+ 1 指定的位置不在此執行個體之內。The current instance does not equal Empty, and startIndex - count+ 1 specifies a position that is not within this instance.

-或--or-

目前的執行個體等於 Empty,且 start 小於 -1 或大於零。The current instance equals Empty and start is less than -1 or greater than zero.

-或--or-

目前的執行個體等於 Empty,且 count 大於 1。The current instance equals Empty and count is greater than 1.

範例

下列範例會尋找子字串中所有出現之字串的索引,從子字串的結尾開始,到子字串的開頭。The following example finds the index of all occurrences of a string in substring, working from the end of the substring to the start of the substring.

// Sample for String::LastIndexOf(String, Int32, Int32)
using namespace System;
int main()
{
   String^ br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
   String^ br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
   String^ str = "Now is the time for all good men to come to the aid of their party.";
   int start;
   int at;
   int count;
   int end;
   start = str->Length - 1;
   end = start / 2 - 1;
   Console::WriteLine( "All occurrences of 'he' from position {0} to {1}.", start, end );
   Console::WriteLine( "{1}{0}{2}{0}{3}{0}", Environment::NewLine, br1, br2, str );
   Console::Write( "The string 'he' occurs at position(s): " );
   count = 0;
   at = 0;
   while ( (start > -1) && (at > -1) )
   {
      count = start - end; //Count must be within the substring.
      at = str->LastIndexOf( "he", start, count );
      if ( at > -1 )
      {
         Console::Write( "{0} ", at );
         start = at - 1;
      }
   }

   Console::Write( "{0} {0} {0}", Environment::NewLine );
}

/*
This example produces the following results:
All occurrences of 'he' from position 66 to 32.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The string 'he' occurs at position(s): 56 45
*/
// Sample for String.LastIndexOf(String, Int32, Int32)
using System;

class Sample {
    public static void Main() {

    string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
    string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
    string str = "Now is the time for all good men to come to the aid of their party.";
    int start;
    int at;
    int count;
    int end;

    start = str.Length-1;
    end = start/2 - 1;
    Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, end);
    Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str);
    Console.Write("The string 'he' occurs at position(s): ");

    count = 0;
    at = 0;
    while((start > -1) && (at > -1))
        {
        count = start - end; //Count must be within the substring.
        at = str.LastIndexOf("he", start, count);
        if (at > -1)
            {
            Console.Write("{0} ", at);
            start = at - 1;
            }
        }
    Console.Write("{0}{0}{0}", Environment.NewLine);
    }
}
/*
This example produces the following results:
All occurrences of 'he' from position 66 to 32.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The string 'he' occurs at position(s): 56 45
*/
' Sample for String.LastIndexOf(String, Int32, Int32)
 _

Class Sample
   
   Public Shared Sub Main()
      
      Dim br1 As String = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-"
      Dim br2 As String = "0123456789012345678901234567890123456789012345678901234567890123456"
      Dim str As String = "Now is the time for all good men to come to the aid of their party."
      Dim start As Integer
      Dim at As Integer
      Dim count As Integer
      Dim [end] As Integer

      start = str.Length - 1
      [end] = start / 2 - 1
      Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, [end])
      Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str)
      Console.Write("The string 'he' occurs at position(s): ")
      
      count = 0
      at = 0
      While start > - 1 And at > - 1
         count = start - [end] 'Count must be within the substring.
         at = str.LastIndexOf("he", start, count)
         If at > - 1 Then
            Console.Write("{0} ", at)
            start = at - 1
         End If
      End While
      Console.Write("{0}{0}{0}", Environment.NewLine)
   End Sub
End Class
'
'This example produces the following results:
'All occurrences of 'he' from position 66 to 32.
'0----+----1----+----2----+----3----+----4----+----5----+----6----+-
'0123456789012345678901234567890123456789012345678901234567890123456
'Now is the time for all good men to come to the aid of their party.
'
'The string 'he' occurs at position(s): 56 45
'
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

搜尋 startIndex 會從這個實例的字元位置開始,並在一開始時繼續進行,直到 value 找到或已 count 檢查字元位置為止。The search begins at the startIndex character position of this instance and proceeds backward toward the beginning until either value is found or count character positions have been examined. 例如,如果 startIndexLength -1,則方法會搜尋 count 字串中最後一個字元的後置字元。For example, if startIndex is Length - 1, the method searches backward count characters from the last character in the string.

這個方法會使用目前的文化特性,執行文字 (區分大小寫且區分文化特性) 搜尋。This method performs a word (case-sensitive and culture-sensitive) search using the current culture.

字元集包含可忽略的字元,這些字元在執行語言或區分文化特性的比較時不列入考慮。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 執行區分文化特性的搜尋時,如果 value 包含可忽略的字元,則結果等於在已移除該字元的情況下搜尋。In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed.

在下列範例中, LastIndexOf 方法是用來找出軟連字號的位置 (U + 00AD) 後接兩個字串中的 "m" 或 "n"。In the following example, the LastIndexOf method is used to find the position of a soft hyphen (U+00AD) followed by an "m" or "n" in two strings. 只有其中一個字串包含選擇性連字號。Only one of the strings contains a soft hyphen. 如果是包含軟連字號的字串,後面接著 "m",則會在 LastIndexOf 搜尋軟連字號之後,傳回 "m" 的索引,並在後面加上 "m"。In the case of the string that includes the soft hyphen followed by an "m", LastIndexOf returns the index of the "m" when searching for the soft hyphen followed by "m".

int position = 0;
string s1 = "ani\u00ADmal";
string s2 = "animal";

// Find the index of the soft hyphen followed by "n".
position = s1.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s1.LastIndexOf("\u00ADn", position, position + 1));

position = s2.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s2.LastIndexOf("\u00ADn", position, position + 1));

// Find the index of the soft hyphen followed by "m".
position = s1.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s1.LastIndexOf("\u00ADm", position, position + 1));

position = s2.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s2.LastIndexOf("\u00ADm", position, position + 1));

// The example displays the following output:
//
// 'm' at position 4
// 1
// 'm' at position 3
// 1
// 'm' at position 4
// 4
// 'm' at position 3
// 3
Dim position As Integer
Dim softHyphen As String = ChrW(&HAD)

Dim s1 As String = "ani" + softHyphen + "mal"
Dim s2 As String = "animal"

' Find the index of the soft hyphen followed by "n".
position = s1.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s1.LastIndexOf(softHyphen + "n", position, position + 1))
End If

position = s2.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s2.LastIndexOf(softHyphen + "n", position, position + 1))
End If

' Find the index of the soft hyphen followed by "m".
position = s1.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s1.LastIndexOf(softHyphen + "m", position, position + 1))
End If

position = s2.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s2.LastIndexOf(softHyphen + "m", position, position + 1))
End If

' The example displays the following output:
'
' 'm' at position 4
' 1
' 'm' at position 3
' 1
' 'm' at position 4
' 4
' 'm' at position 3
' 3

給呼叫者的注意事項

使用字串的最佳做法中所述,我們建議您避免呼叫替代預設值的字串比較方法,而改為呼叫需要明確指定參數的方法。As explained in Best Practices for Using Strings, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. 若要使用目前文化特性的比較規則來執行這項作業,請呼叫方法多載, LastIndexOf(String, Int32, Int32, StringComparison) CurrentCulture 其參數的值為 comparisonTypeTo perform this operation by using the comparison rules of the current culture, call the LastIndexOf(String, Int32, Int32, StringComparison) method overload with a value of CurrentCulture for its comparisonType parameter.

另請參閱

適用於

LastIndexOf(Char, Int32, Int32)

報告這個執行個體的子字串中,指定的 Unicode 字元最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of the specified Unicode character in a substring within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串開頭指定數目的字元位置進行。The search starts at a specified character position and proceeds backward toward the beginning of the string for a specified number of character positions.

public:
 int LastIndexOf(char value, int startIndex, int count);
public int LastIndexOf (char value, int startIndex, int count);
member this.LastIndexOf : char * int * int -> int
Public Function LastIndexOf (value As Char, startIndex As Integer, count As Integer) As Integer

參數

value
Char

要搜尋的 Unicode 字元。The Unicode character to seek.

startIndex
Int32

搜尋的開始位置。The starting position of the search. 搜尋會從 startIndex 朝這個執行個體的開頭進行。The search proceeds from startIndex toward the beginning of this instance.

count
Int32

要檢視的字元位置數目。The number of character positions to examine.

傳回

Int32

如果找到該字元,則為 value 的以零為起始索引位置,如果找不到該字元或者目前的執行個體等於 Empty,則為 -1。The zero-based index position of value if that character is found, or -1 if it is not found or if the current instance equals Empty.

例外狀況

目前的執行個體不等於 Empty,且 startIndex 小於零,或者大於或等於這個執行個體的長度。The current instance does not equal Empty, and startIndex is less than zero or greater than or equal to the length of this instance.

-或--or-

目前的執行個體不等於 Empty,且 startIndex - count + 1 小於零。The current instance does not equal Empty, and startIndex - count + 1 is less than zero.

範例

下列範例會尋找子字串中所有出現字元的索引,從子字串的結尾開始,到子字串的開頭。The following example finds the index of all occurrences of a character in a substring, working from the end of the substring to the start of the substring.

// Sample for String::LastIndexOf(Char, Int32, Int32)
using namespace System;
int main()
{
   String^ br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
   String^ br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
   String^ str = "Now is the time for all good men to come to the aid of their party.";
   int start;
   int at;
   int count;
   int end;
   start = str->Length - 1;
   end = start / 2 - 1;
   Console::WriteLine( "All occurrences of 't' from position {0} to {1}.", start, end );
   Console::WriteLine( "\n{0}\n{1}\n{2}", br1, br2, str );
   Console::Write( "The letter 't' occurs at position(s): " );
   count = 0;
   at = 0;
   while ( (start > -1) && (at > -1) )
   {
      count = start - end; //Count must be within the substring.
      at = str->LastIndexOf( 't', start, count );
      if ( at > -1 )
      {
         Console::Write( " {0} ", at );
         start = at - 1;
      }
   }
}

/*
This example produces the following results:
All occurrences of 't' from position 66 to 32.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The letter 't' occurs at position(s): 64 55 44 41 33


*/
// Sample for String.LastIndexOf(Char, Int32, Int32)
using System;

class Sample {
    public static void Main() {

    string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
    string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
    string str = "Now is the time for all good men to come to the aid of their party.";
    int start;
    int at;
    int count;
    int end;

    start = str.Length-1;
    end = start/2 - 1;
    Console.WriteLine("All occurrences of 't' from position {0} to {1}.", start, end);
    Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str);
    Console.Write("The letter 't' occurs at position(s): ");

    count = 0;
    at = 0;
    while((start > -1) && (at > -1))
        {
        count = start - end; //Count must be within the substring.
        at = str.LastIndexOf('t', start, count);
        if (at > -1)
            {
            Console.Write("{0} ", at);
            start = at - 1;
            }
        }
    Console.Write("{0}{0}{0}", Environment.NewLine);
    }
}
/*
This example produces the following results:
All occurrences of 't' from position 66 to 32.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The letter 't' occurs at position(s): 64 55 44 41 33


*/
' Sample for String.LastIndexOf(Char, Int32, Int32)
 _

Class Sample
   
   Public Shared Sub Main()
      
      Dim br1 As String = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-"
      Dim br2 As String = "0123456789012345678901234567890123456789012345678901234567890123456"
      Dim str As String = "Now is the time for all good men to come to the aid of their party."
      Dim start As Integer
      Dim at As Integer
      Dim count As Integer
      Dim [end] As Integer

      start = str.Length - 1
      [end] = start / 2 - 1
      Console.WriteLine("All occurrences of 't' from position {0} to {1}.", start, [end])
      Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str)
      Console.Write("The letter 't' occurs at position(s): ")
      
      count = 0
      at = 0
      While start > - 1 And at > - 1
         count = start - [end] 'Count must be within the substring.
         at = str.LastIndexOf("t"c, start, count)
         If at > - 1 Then
            Console.Write("{0} ", at)
            start = at - 1
         End If
      End While
      Console.Write("{0}{0}{0}", Environment.NewLine)
   End Sub
End Class
'
'This example produces the following results:
'All occurrences of 't' from position 66 to 32.
'0----+----1----+----2----+----3----+----4----+----5----+----6----+-
'0123456789012345678901234567890123456789012345678901234567890123456
'Now is the time for all good men to come to the aid of their party.
'
'The letter 't' occurs at position(s): 64 55 44 41 33
'
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

這個方法會開始在 startIndex 字元位置搜尋,並在這個實例的開頭繼續往前移動,直到 value 找到或已 count 檢查字元位置為止。This method begins searching at the startIndex character position and proceeds backward toward the beginning of this instance until either value is found or count character positions have been examined. 例如,如果 startIndexLength -1,則方法會搜尋 count 字串中最後一個字元的後置字元。For example, if startIndex is Length - 1, the method searches backward count characters from the last character in the string. 搜尋會區分大小寫。The search is case-sensitive.

這個方法會執行不區分文化特性) 搜尋的序數 (,其中只有當 Unicode 純量值相同時,才會將字元視為等於另一個字元。This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar value are the same. 若要執行區分文化特性的搜尋,請使用 CompareInfo.LastIndexOf 方法,其中代表 precomposed 字元的 Unicode 純量值(例如連字號 "Æ" (U + 00C6) )可能會被視為等於正確順序中任何相符字元的元件,例如 "AE" (U + 0041,U + 0045) ,視文化特性而定。To perform a culture-sensitive search, use the CompareInfo.LastIndexOf method, where a Unicode scalar value representing a precomposed character, such as the ligature "Æ" (U+00C6), might be considered equivalent to any occurrence of the character's components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture.

另請參閱

適用於

LastIndexOf(String, StringComparison)

報告目前 String 物件中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index of the last occurrence of a specified string within the current String object. 參數會指定要用於指定字串的搜尋類型。A parameter specifies the type of search to use for the specified string.

public:
 int LastIndexOf(System::String ^ value, StringComparison comparisonType);
public int LastIndexOf (string value, StringComparison comparisonType);
member this.LastIndexOf : string * StringComparison -> int
Public Function LastIndexOf (value As String, comparisonType As StringComparison) As Integer

參數

value
String

要搜尋的字串。The string to seek.

comparisonType
StringComparison

其中一個列舉值,指定搜尋規則。One of the enumeration values that specifies the rules for the search.

傳回

Int32

如果找到該字串,則為 value 參數的以零為起始的起始索引位置,否則為 -1。The zero-based starting index position of the value parameter if that string is found, or -1 if it is not.

例外狀況

valuenullvalue is null.

comparisonType 不是有效的 StringComparison 值。comparisonType is not a valid StringComparison value.

範例

下列範例示範三個方法的多載 LastIndexOf ,此方法會使用不同的列舉值來尋找另一個字串中的最後一個字串 StringComparisonThe following example demonstrates three overloads of the LastIndexOf method that find the last occurrence of a string within another string using different values of the StringComparison enumeration.

// This code example demonstrates the 
// System.String.LastIndexOf(String, ..., StringComparison) methods.

using System;
using System.Threading;
using System.Globalization;

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the last occurrence of a character using different " + 
                   "values of StringComparison.";
    string resultFmt = "Comparison: {0,-28} Location: {1,3}";

// Define a string to search for.
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    string CapitalAWithRing = "\u00c5"; 

// Define a string to search. 
// The result of combining the characters LATIN SMALL LETTER A and COMBINING 
// RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
// LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
    string cat = "A Cheshire c" + "\u0061\u030a" + "t";
    int loc = 0;
    StringComparison[] scValues = {
        StringComparison.CurrentCulture,
        StringComparison.CurrentCultureIgnoreCase,
        StringComparison.InvariantCulture,
        StringComparison.InvariantCultureIgnoreCase,
        StringComparison.Ordinal,
        StringComparison.OrdinalIgnoreCase };

// Clear the screen and display an introduction.
    Console.Clear();
    Console.WriteLine(intro);

// Display the current culture because culture affects the result. For example, 
// try this code example with the "sv-SE" (Swedish-Sweden) culture.

    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
    Console.WriteLine("The current culture is \"{0}\" - {1}.", 
                       Thread.CurrentThread.CurrentCulture.Name,
                       Thread.CurrentThread.CurrentCulture.DisplayName);

// Display the string to search for and the string to search.
    Console.WriteLine("Search for the string \"{0}\" in the string \"{1}\"", 
                       CapitalAWithRing, cat);
    Console.WriteLine();

// Note that in each of the following searches, we look for 
// LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains 
// LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates 
// the string was not found.
// Search using different values of StringComparsion. Specify the start 
// index and count. 

    Console.WriteLine("Part 1: Start index and count are specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. Specify the 
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }
    }
}

/*
Note: This code example was executed on a console whose user interface 
culture is "en-US" (English-United States).

This code example produces the following results:

Find the last occurrence of a character using different values of StringComparison.
The current culture is "en-US" - English (United States).
Search for the string "Å" in the string "A Cheshire ca°t"

Part 1: Start index and count are specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

Part 2: Start index is specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

Part 3: Neither start index nor count is specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

*/
' This code example demonstrates the 
' System.String.LastIndexOf(String, ..., StringComparison) methods.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the last occurrence of a character using different " & _
                              "values of StringComparison."
        Dim resultFmt As String = "Comparison: {0,-28} Location: {1,3}"
        
        ' Define a string to search for.
        ' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
        Dim CapitalAWithRing As String = "Å"
        
        ' Define a string to search. 
        ' The result of combining the characters LATIN SMALL LETTER A and COMBINING 
        ' RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
        ' LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
        Dim cat As String = "A Cheshire c" & "å" & "t"
        Dim loc As Integer = 0
        Dim scValues As StringComparison() =  { _
                        StringComparison.CurrentCulture, _
                        StringComparison.CurrentCultureIgnoreCase, _
                        StringComparison.InvariantCulture, _
                        StringComparison.InvariantCultureIgnoreCase, _
                        StringComparison.Ordinal, _
                        StringComparison.OrdinalIgnoreCase }
        Dim sc As StringComparison
        
        ' Clear the screen and display an introduction.
        Console.Clear()
        Console.WriteLine(intro)
        
        ' Display the current culture because culture affects the result. For example, 
        ' try this code example with the "sv-SE" (Swedish-Sweden) culture.
        Thread.CurrentThread.CurrentCulture = New CultureInfo("en-US")
        Console.WriteLine("The current culture is ""{0}"" - {1}.", _
                           Thread.CurrentThread.CurrentCulture.Name, _
                           Thread.CurrentThread.CurrentCulture.DisplayName)
        
        ' Display the string to search for and the string to search.
        Console.WriteLine("Search for the string ""{0}"" in the string ""{1}""", _
                           CapitalAWithRing, cat)
        Console.WriteLine()
        
        ' Note that in each of the following searches, we look for 
        ' LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains 
        ' LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates 
        ' the string was not found.
        ' Search using different values of StringComparsion. Specify the start 
        ' index and count. 
        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparsion. Specify the 
        ' start index. 
        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparsion. 
        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
    
    End Sub
End Class

'
'Note: This code example was executed on a console whose user interface 
'culture is "en-US" (English-United States).
'
'This code example produces the following results:
'
'Find the last occurrence of a character using different values of StringComparison.
'The current culture is "en-US" - English (United States).
'Search for the string "Å" in the string "A Cheshire ca°t"
'
'Part 1: Start index and count are specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'
'Part 2: Start index is specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'
'Part 3: Neither start index nor count is specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

comparisonType參數指定要 value 使用下列參數來搜尋參數:The comparisonType parameter specifies to search for the value parameter using:

  • 目前或不變的文化特性。The current or invariant culture.
  • 區分大小寫或不區分大小寫的搜尋。A case-sensitive or case-insensitive search.
  • 單字或序數比較規則。Word or ordinal comparison rules.

搜尋會從這個實例的最後一個字元位置開始,並在找到任何一項 value 或檢查第一個字元位置之前向前移動。The search begins at the last character position of this instance and proceeds backward toward the beginning until either value is found or the first character position has been examined.

給呼叫者的注意事項

字元集包含可忽略的字元,這些字元在執行語言或區分文化特性的比較時不列入考慮。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 執行區分文化特性的搜尋 (也就是說,如果 options 不是 OrdinalOrdinalIgnoreCase) 時,如果 value 包含可忽略的字元,則結果等於在已移除該字元的情況下搜尋。In a culture-sensitive search (that is, if options is not Ordinal or OrdinalIgnoreCase), if value contains an ignorable character, the result is equivalent to searching with that character removed.

在下列範例中, LastIndexOf(String, StringComparison) 方法是用來尋找兩個子字串 (軟連字號後面接著 "n",然後在兩個字串中 ) 以 "m" 為開頭的軟連字號。In the following example, the LastIndexOf(String, StringComparison) method is used to find two substrings (a soft hyphen followed by "n", and a soft hyphen followed by "m") in two strings. 只有其中一個字串包含選擇性連字號。Only one of the strings contains a soft hyphen. 如果範例是在 .NET Framework 4 或更新版本上執行,因為軟連字號是可忽略的字元,所以區分文化特性的搜尋會傳回相同的值,如果未在搜尋字串中包含軟連字號,則會傳回相同的值。If the example is run on .NET Framework 4 or later, because the soft hyphen is an ignorable character, a culture-sensitive search returns the same value that it would return if the soft hyphen were not included in the search string. 但是,序數搜尋會在一個字串中成功找到軟連字號,並回報它不存在於第二個字串中。An ordinal search, however, successfully finds the soft hyphen in one string and reports that it is absent from the second string.

[!程式碼-csharpsystem.string. LastIndexOf # 26][! code-vbsystem.string. LastIndexOf # 26][!code-csharpSystem.String.LastIndexOf#26] [!code-vbSystem.String.LastIndexOf#26]

適用於

LastIndexOf(Char)

報告這個執行個體中指定之 Unicode 字元最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified Unicode character within this instance.

public:
 int LastIndexOf(char value);
public int LastIndexOf (char value);
member this.LastIndexOf : char -> int
Public Function LastIndexOf (value As Char) As Integer

參數

value
Char

要搜尋的 Unicode 字元。The Unicode character to seek.

傳回

Int32

如果找到該字元,則為 value 以零為起始的索引位置,如果找不到為 -1。The zero-based index position of value if that character is found, or -1 if it is not.

範例

下列範例 ExtractFilename 會定義方法,此方法會使用 LastIndexOf(Char) 方法來尋找字串中的最後一個目錄分隔符號,並解壓縮字串的檔案名。The following example defines an ExtractFilename method that uses the LastIndexOf(Char) method to find the last directory separator character in a string and to extract the string's file name. 如果檔案存在,則方法會傳回檔案名,而不包含其路徑。If the file exists, the method returns the file name without its path.

using System;
using System.IO;

public class TestLastIndexOf
{
   public static void Main()
   {
      string filename;
      
      filename = ExtractFilename(@"C:\temp\");
      Console.WriteLine("{0}", String.IsNullOrEmpty(filename) ? "<none>" : filename);
      
      filename = ExtractFilename(@"C:\temp\delegate.txt"); 
      Console.WriteLine("{0}", String.IsNullOrEmpty(filename) ? "<none>" : filename);

      filename = ExtractFilename("delegate.txt");      
      Console.WriteLine("{0}", String.IsNullOrEmpty(filename) ? "<none>" : filename);
      
      filename = ExtractFilename(@"C:\temp\notafile.txt");
      Console.WriteLine("{0}", String.IsNullOrEmpty(filename) ? "<none>" : filename);
   }

   public static string ExtractFilename(string filepath)
   {
      // If path ends with a "\", it's a path only so return String.Empty.
      if (filepath.Trim().EndsWith(@"\"))
         return String.Empty;
      
      // Determine where last backslash is.
      int position = filepath.LastIndexOf('\\');
      // If there is no backslash, assume that this is a filename.
      if (position == -1)
      {
         // Determine whether file exists in the current directory.
         if (File.Exists(Environment.CurrentDirectory + Path.DirectorySeparatorChar + filepath)) 
            return filepath;
         else
            return String.Empty;
      }
      else
      {
         // Determine whether file exists using filepath.
         if (File.Exists(filepath))
            // Return filename without file path.
            return filepath.Substring(position + 1);
         else
            return String.Empty;
      }
   }
}
Imports System.IO

Public Module Test
   Public Sub Main()
      Dim filename As String 
      
      filename = ExtractFilename("C:\temp\")
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))
      
      filename = ExtractFilename("C:\temp\delegate.txt") 
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))

      filename = ExtractFilename("delegate.txt")      
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))
      
      filename = ExtractFilename("C:\temp\notafile.txt")
      Console.WriteLine("{0}", IIf(String.IsNullOrEmpty(fileName), "<none>", filename))
   End Sub
   
   Public Function ExtractFilename(filepath As String) As String
      ' If path ends with a "\", it's a path only so return String.Empty.
      If filepath.Trim().EndsWith("\") Then Return String.Empty
      
      ' Determine where last backslash is.
      Dim position As Integer = filepath.LastIndexOf("\"c)
      ' If there is no backslash, assume that this is a filename.
      If position = -1 Then
         ' Determine whether file exists in the current directory.
         If File.Exists(Environment.CurrentDirectory + Path.DirectorySeparatorChar + filepath) Then
            Return filepath
         Else
            Return String.Empty
         End If
      Else
         ' Determine whether file exists using filepath.
         If File.Exists(filepath) Then
            ' Return filename without file path.
            Return filepath.Substring(position + 1)
         Else
            Return String.Empty
         End If                     
      End If
   End Function
End Module 
' The example displays the following output:
'        delegate.txt

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

這個方法會開始在這個實例的最後一個字元位置進行搜尋,並且在找到任何一個位置 value 或檢查第一個字元位置之前,繼續往前移動。This method begins searching at the last character position of this instance and proceeds backward toward the beginning until either value is found or the first character position has been examined. 搜尋會區分大小寫。The search is case-sensitive.

這個方法會執行不區分文化特性) 搜尋的序數 (,其中只有當 Unicode 純量值相同時,才會將字元視為等於另一個字元。This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar values are the same. 若要執行區分文化特性的搜尋,請使用 CompareInfo.LastIndexOf 方法,其中代表 precomposed 字元的 Unicode 純量值(例如連字號 "Æ" (U + 00C6) )可能會被視為等於正確順序中任何相符字元的元件,例如 "AE" (U + 0041,U + 0045) ,視文化特性而定。To perform a culture-sensitive search, use the CompareInfo.LastIndexOf method, where a Unicode scalar value representing a precomposed character, such as the ligature "Æ" (U+00C6), might be considered equivalent to any occurrence of the character's components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture.

另請參閱

適用於

LastIndexOf(Char, Int32)

報告這個執行個體中指定之 Unicode 字元最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified Unicode character within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串的開頭進行。The search starts at a specified character position and proceeds backward toward the beginning of the string.

public:
 int LastIndexOf(char value, int startIndex);
public int LastIndexOf (char value, int startIndex);
member this.LastIndexOf : char * int -> int
Public Function LastIndexOf (value As Char, startIndex As Integer) As Integer

參數

value
Char

要搜尋的 Unicode 字元。The Unicode character to seek.

startIndex
Int32

搜尋的開始位置。The starting position of the search. 搜尋會從 startIndex 朝這個執行個體的開頭進行。The search proceeds from startIndex toward the beginning of this instance.

傳回

Int32

如果找到該字元,則為 value 的以零為起始索引位置,如果找不到該字元或者目前的執行個體等於 Empty,則為 -1。The zero-based index position of value if that character is found, or -1 if it is not found or if the current instance equals Empty.

例外狀況

目前的執行個體不等於 Empty,且 startIndex 小於零,或者大於或等於這個執行個體的長度。The current instance does not equal Empty, and startIndex is less than zero or greater than or equal to the length of this instance.

範例

下列範例會在字串中尋找所有出現字元的索引,從字串的結尾開始,一直到字串開頭。The following example finds the index of all occurrences of a character in a string, working from the end of the string to the start of the string.

// Sample for String::LastIndexOf(Char, Int32)
using namespace System;
int main()
{
   String^ br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
   String^ br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
   String^ str = "Now is the time for all good men to come to the aid of their party.";
   int start;
   int at;
   start = str->Length - 1;
   Console::WriteLine( "All occurrences of 't' from position {0} to 0.", start );
   Console::WriteLine( "{0}\n{1}\n{2}\n", br1, br2, str );
   Console::Write( "The letter 't' occurs at position(s): " );
   at = 0;
   while ( (start > -1) && (at > -1) )
   {
      at = str->LastIndexOf( 't', start );
      if ( at > -1 )
      {
         Console::Write( " {0} ", at );
         start = at - 1;
      }
   }
}

/*
This example produces the following results:
All occurrences of 't' from position 66 to 0.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The letter 't' occurs at position(s): 64 55 44 41 33 11 7
*/
// Sample for String.LastIndexOf(Char, Int32)
using System;

class Sample {
    public static void Main() {

    string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
    string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
    string str = "Now is the time for all good men to come to the aid of their party.";
    int start;
    int at;

    start = str.Length-1;
    Console.WriteLine("All occurrences of 't' from position {0} to 0.", start);
    Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str);
    Console.Write("The letter 't' occurs at position(s): ");

    at = 0;
    while((start > -1) && (at > -1))
        {
        at = str.LastIndexOf('t', start);
        if (at > -1)
            {
            Console.Write("{0} ", at);
            start = at - 1;
            }
        }
    Console.Write("{0}{0}{0}", Environment.NewLine);
    }
}
/*
This example produces the following results:
All occurrences of 't' from position 66 to 0.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The letter 't' occurs at position(s): 64 55 44 41 33 11 7
*/
' Sample for String.LastIndexOf(Char, Int32)
Imports System 
 _

Class Sample
   
   Public Shared Sub Main()
      
      Dim br1 As String = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-"
      Dim br2 As String = "0123456789012345678901234567890123456789012345678901234567890123456"
      Dim str As String = "Now is the time for all good men to come to the aid of their party."
      Dim start As Integer
      Dim at As Integer
      
      start = str.Length - 1
      Console.WriteLine("All occurrences of 't' from position {0} to 0.", start)
      Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str)
      Console.Write("The letter 't' occurs at position(s): ")
      
      at = 0
      While start > - 1 And at > - 1
         at = str.LastIndexOf("t"c, start)
         If at > - 1 Then
            Console.Write("{0} ", at)
            start = at - 1
         End If
      End While
      Console.Write("{0}{0}{0}", Environment.NewLine)
   End Sub
End Class
'
'This example produces the following results:
'All occurrences of 't' from position 66 to 0.
'0----+----1----+----2----+----3----+----4----+----5----+----6----+-
'0123456789012345678901234567890123456789012345678901234567890123456
'Now is the time for all good men to come to the aid of their party.
'
'The letter 't' occurs at position(s): 64 55 44 41 33 11 7
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1. 這個方法會開始在 startIndex 此實例的字元位置進行搜尋,並在目前實例的開頭繼續往前移動,直到 value 找到或檢查第一個字元位置為止。This method begins searching at the startIndex character position of this instance and proceeds backward toward the beginning of the current instance until either value is found or the first character position has been examined. 例如,如果 startIndexLength -1,則方法會搜尋字串中最後一個字元到開頭的每個字元。For example, if startIndex is Length - 1, the method searches every character from the last character in the string to the beginning. 搜尋會區分大小寫。The search is case-sensitive.

這個方法會執行不區分文化特性) 搜尋的序數 (,其中只有當 Unicode 純量值相同時,才會將字元視為等於另一個字元。This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar values are the same. 若要執行區分文化特性的搜尋,請使用 CompareInfo.LastIndexOf 方法,其中代表 precomposed 字元的 Unicode 純量值(例如連字號 "Æ" (U + 00C6) )可能會被視為等於正確順序中任何相符字元的元件,例如 "AE" (U + 0041,U + 0045) ,視文化特性而定。To perform a culture-sensitive search, use the CompareInfo.LastIndexOf method, where a Unicode scalar value representing a precomposed character, such as the ligature "Æ" (U+00C6), might be considered equivalent to any occurrence of the character's components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture.

另請參閱

適用於

LastIndexOf(String)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance.

public:
 int LastIndexOf(System::String ^ value);
public int LastIndexOf (string value);
member this.LastIndexOf : string -> int
Public Function LastIndexOf (value As String) As Integer

參數

value
String

要搜尋的字串。The string to seek.

傳回

Int32

如果找到該字串,則為 value 以零為起始的起始索引位置,如未找到,則為 -1。The zero-based starting index position of value if that string is found, or -1 if it is not.

例外狀況

valuenullvalue is null.

範例

下列範例會從字串中移除開頭和結尾的 HTML 標籤(如果標記開頭和結尾)。The following example removes opening and closing HTML tags from a string if the tags begin and end the string. 如果字串的結尾是右括弧字元 ( ">" ) ,則範例會使用 LastIndexOf 方法來尋找結束標記的開頭。If a string ends with a closing bracket character (">"), the example uses the LastIndexOf method to locate the start of the end tag.

using System;

public class Example 
{
   public static void Main() 
   {
      string[] strSource = { "<b>This is bold text</b>", "<H1>This is large Text</H1>",
               "<b><i><font color=green>This has multiple tags</font></i></b>",
               "<b>This has <i>embedded</i> tags.</b>",
               "This line ends with a greater than symbol and should not be modified>" };

      // Strip HTML start and end tags from each string if they are present.
      foreach (string s in strSource)
      {
         Console.WriteLine("Before: " + s);
         string item = s;
         // Use EndsWith to find a tag at the end of the line.
         if (item.Trim().EndsWith(">")) 
         {
            // Locate the opening tag.
            int endTagStartPosition = item.LastIndexOf("</");
            // Remove the identified section, if it is valid.
            if (endTagStartPosition >= 0 )
               item = item.Substring(0, endTagStartPosition);

            // Use StartsWith to find the opening tag.
            if (item.Trim().StartsWith("<"))
            {
               // Locate the end of opening tab.
               int openTagEndPosition = item.IndexOf(">");
               // Remove the identified section, if it is valid.
               if (openTagEndPosition >= 0)
                  item = item.Substring(openTagEndPosition + 1);
            }      
         }
         // Display the trimmed string.
         Console.WriteLine("After: " + item);
         Console.WriteLine();
      }                   
   }
}
// The example displays the following output:
//    Before: <b>This is bold text</b>
//    After: This is bold text
//    
//    Before: <H1>This is large Text</H1>
//    After: This is large Text
//    
//    Before: <b><i><font color=green>This has multiple tags</font></i></b>
//    After: <i><font color=green>This has multiple tags</font></i>
//    
//    Before: <b>This has <i>embedded</i> tags.</b>
//    After: This has <i>embedded</i> tags.
//    
//    Before: This line ends with a greater than symbol and should not be modified>
//    After: This line ends with a greater than symbol and should not be modified>
Module Example
   Public Sub Main()
      Dim strSource As String() = { "<b>This is bold text</b>", _
                    "<H1>This is large Text</H1>", _
                    "<b><i><font color=green>This has multiple tags</font></i></b>", _
                    "<b>This has <i>embedded</i> tags.</b>", _
                    "This line ends with a greater than symbol and should not be modified>" }

      ' Strip HTML start and end tags from each string if they are present.
      For Each s As String In strSource
         Console.WriteLine("Before: " + s)
         ' Use EndsWith to find a tag at the end of the line.
         If s.Trim().EndsWith(">") Then 
            ' Locate the opening tag.
            Dim endTagStartPosition As Integer = s.LastIndexOf("</")
            ' Remove the identified section if it is valid.
            If endTagStartPosition >= 0 Then
               s = s.Substring(0, endTagStartPosition)
            End If
            
            ' Use StartsWith to find the opening tag.
            If s.Trim().StartsWith("<") Then
               ' Locate the end of opening tab.
               Dim openTagEndPosition As Integer = s.IndexOf(">")
               ' Remove the identified section if it is valid.
               If openTagEndPosition >= 0 Then
                  s = s.Substring(openTagEndPosition + 1)
               End If   
            End If      
         End If
         ' Display the trimmed string.
         Console.WriteLine("After: " + s)
         Console.WriteLine()
      Next                   
   End Sub
End Module
' The example displays the following output:
'    Before: <b>This is bold text</b>
'    After: This is bold text
'    
'    Before: <H1>This is large Text</H1>
'    After: This is large Text
'    
'    Before: <b><i><font color=green>This has multiple tags</font></i></b>
'    After: <i><font color=green>This has multiple tags</font></i>
'    
'    Before: <b>This has <i>embedded</i> tags.</b>
'    After: This has <i>embedded</i> tags.
'    
'    Before: This line ends with a greater than symbol and should not be modified>
'    After: This line ends with a greater than symbol and should not be modified>

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

搜尋會從這個實例的最後一個字元位置開始,並在找到任何一項 value 或檢查第一個字元位置之前向前移動。The search begins at the last character position of this instance and proceeds backward toward the beginning until either value is found or the first character position has been examined.

這個方法會使用目前的文化特性,執行文字 (區分大小寫且區分文化特性) 搜尋。This method performs a word (case-sensitive and culture-sensitive) search using the current culture.

字元集包含可忽略的字元,這些字元在執行語言或區分文化特性的比較時不列入考慮。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 執行區分文化特性的搜尋時,如果 value 包含可忽略的字元,則結果等於在已移除該字元的情況下搜尋。In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed.

在下列範例中, LastIndexOf(String) 方法是用來尋找兩個子字串 (在兩個字串中的軟連字號後面加上 "n" 和軟連字號,後面接著 "m" ) 。In the following example, the LastIndexOf(String) method is used to find two substrings (a soft hyphen followed by "n" and a soft hyphen followed by "m") in two strings. 只有其中一個字串包含選擇性連字號。Only one of the strings contains a soft hyphen. 如果範例是在 .NET Framework 4 或更新版本上執行,則在每個案例中,因為軟連字號是可忽略的字元,所以結果與未包含軟連字號的結果相同 valueIf the example is run on .NET Framework 4 or later, in each case, because the soft hyphen is an ignorable character, the result is the same as if the soft hyphen had not been included in value.

string s1 = "ani\u00ADmal";
string s2 = "animal";

// Find the index of the last soft hyphen followed by "n".
Console.WriteLine(s1.LastIndexOf("\u00ADn"));
Console.WriteLine(s2.LastIndexOf("\u00ADn"));

// Find the index of the last soft hyphen followed by "m".
Console.WriteLine(s1.LastIndexOf("\u00ADm"));
Console.WriteLine(s2.LastIndexOf("\u00ADm"));

// The example displays the following output:
//
// 1
// 1
// 4
// 3
Dim softHyphen As String = ChrW(&HAD)
Dim s1 As String = "ani" + softHyphen + "mal"
Dim s2 As String = "animal"

' Find the index of the last soft hyphen followed by "n".
Console.WriteLine(s1.LastIndexOf(softHyphen + "n"))
Console.WriteLine(s2.LastIndexOf(softHyphen + "n"))

' Find the index of the last soft hyphen followed by "m".
Console.WriteLine(s1.LastIndexOf(softHyphen + "m"))
Console.WriteLine(s2.LastIndexOf(softHyphen + "m"))

' The example displays the following output:
'
' 1
' 1
' 4
' 3

給呼叫者的注意事項

使用字串的最佳做法中所述,我們建議您避免呼叫替代預設值的字串比較方法,而改為呼叫需要明確指定參數的方法。As explained in Best Practices for Using Strings, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. 若要使用目前文化特性的比較規則,在字串實例中尋找子字串的最後一個索引,請使用的值來呼叫方法多載,以做 LastIndexOf(String, StringComparison) CurrentCulture 為其參數的值 comparisonTypeTo find the last index of a substring within a string instance by using the comparison rules of the current culture, call the LastIndexOf(String, StringComparison) method overload with a value of CurrentCulture for its comparisonType parameter.

另請參閱

適用於

LastIndexOf(String, Int32, Int32, StringComparison)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串開頭指定數目的字元位置進行。The search starts at a specified character position and proceeds backward toward the beginning of the string for the specified number of character positions. 參數會指定搜尋指定字串時要執行的比較類型。A parameter specifies the type of comparison to perform when searching for the specified string.

public:
 int LastIndexOf(System::String ^ value, int startIndex, int count, StringComparison comparisonType);
public int LastIndexOf (string value, int startIndex, int count, StringComparison comparisonType);
member this.LastIndexOf : string * int * int * StringComparison -> int
Public Function LastIndexOf (value As String, startIndex As Integer, count As Integer, comparisonType As StringComparison) As Integer

參數

value
String

要搜尋的字串。The string to seek.

startIndex
Int32

搜尋開始位置。The search starting position. 搜尋會從 startIndex 朝這個執行個體的開頭進行。The search proceeds from startIndex toward the beginning of this instance.

count
Int32

要檢視的字元位置數目。The number of character positions to examine.

comparisonType
StringComparison

其中一個列舉值,指定搜尋規則。One of the enumeration values that specifies the rules for the search.

傳回

Int32

如果找到該字串,則為 value 參數以零為起始的索引位置,如果找不到該字串或者目前的執行個體等於 Empty,則為 -1。The zero-based starting index position of the value parameter if that string is found, or -1 if it is not found or if the current instance equals Empty.

例外狀況

valuenullvalue is null.

count 為負。count is negative.

-或--or-

目前的執行個體不等於 Empty,且 startIndex 為負。The current instance does not equal Empty, and startIndex is negative.

-或--or-

目前的執行個體不等於 Empty,且 startIndex 大於這個執行個體的長度。The current instance does not equal Empty, and startIndex is greater than the length of this instance.

-或--or-

目前的執行個體不等於 Empty,且 startIndex + 1 - count 指定的位置不在此執行個體之內。The current instance does not equal Empty, and startIndex + 1 - count specifies a position that is not within this instance.

-或--or-

目前的執行個體等於 Empty,且 start 小於 -1 或大於零。The current instance equals Empty and start is less than -1 or greater than zero.

-或--or-

目前的執行個體等於 Empty,且 count 大於 1。The current instance equals Empty and count is greater than 1.

comparisonType 不是有效的 StringComparison 值。comparisonType is not a valid StringComparison value.

範例

下列範例示範三個方法的多載 LastIndexOf ,此方法會使用不同的列舉值來尋找另一個字串中的最後一個字串 StringComparisonThe following example demonstrates three overloads of the LastIndexOf method that find the last occurrence of a string within another string using different values of the StringComparison enumeration.

// This code example demonstrates the 
// System.String.LastIndexOf(String, ..., StringComparison) methods.

using System;
using System.Threading;
using System.Globalization;

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the last occurrence of a character using different " + 
                   "values of StringComparison.";
    string resultFmt = "Comparison: {0,-28} Location: {1,3}";

// Define a string to search for.
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    string CapitalAWithRing = "\u00c5"; 

// Define a string to search. 
// The result of combining the characters LATIN SMALL LETTER A and COMBINING 
// RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
// LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
    string cat = "A Cheshire c" + "\u0061\u030a" + "t";
    int loc = 0;
    StringComparison[] scValues = {
        StringComparison.CurrentCulture,
        StringComparison.CurrentCultureIgnoreCase,
        StringComparison.InvariantCulture,
        StringComparison.InvariantCultureIgnoreCase,
        StringComparison.Ordinal,
        StringComparison.OrdinalIgnoreCase };

// Clear the screen and display an introduction.
    Console.Clear();
    Console.WriteLine(intro);

// Display the current culture because culture affects the result. For example, 
// try this code example with the "sv-SE" (Swedish-Sweden) culture.

    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
    Console.WriteLine("The current culture is \"{0}\" - {1}.", 
                       Thread.CurrentThread.CurrentCulture.Name,
                       Thread.CurrentThread.CurrentCulture.DisplayName);

// Display the string to search for and the string to search.
    Console.WriteLine("Search for the string \"{0}\" in the string \"{1}\"", 
                       CapitalAWithRing, cat);
    Console.WriteLine();

// Note that in each of the following searches, we look for 
// LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains 
// LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates 
// the string was not found.
// Search using different values of StringComparsion. Specify the start 
// index and count. 

    Console.WriteLine("Part 1: Start index and count are specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. Specify the 
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, cat.Length-1, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparsion. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.LastIndexOf(CapitalAWithRing, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }
    }
}

/*
Note: This code example was executed on a console whose user interface 
culture is "en-US" (English-United States).

This code example produces the following results:

Find the last occurrence of a character using different values of StringComparison.
The current culture is "en-US" - English (United States).
Search for the string "Å" in the string "A Cheshire ca°t"

Part 1: Start index and count are specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

Part 2: Start index is specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

Part 3: Neither start index nor count is specified.
Comparison: CurrentCulture               Location:  -1
Comparison: CurrentCultureIgnoreCase     Location:  12
Comparison: InvariantCulture             Location:  -1
Comparison: InvariantCultureIgnoreCase   Location:  12
Comparison: Ordinal                      Location:  -1
Comparison: OrdinalIgnoreCase            Location:  -1

*/
' This code example demonstrates the 
' System.String.LastIndexOf(String, ..., StringComparison) methods.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the last occurrence of a character using different " & _
                              "values of StringComparison."
        Dim resultFmt As String = "Comparison: {0,-28} Location: {1,3}"
        
        ' Define a string to search for.
        ' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
        Dim CapitalAWithRing As String = "Å"
        
        ' Define a string to search. 
        ' The result of combining the characters LATIN SMALL LETTER A and COMBINING 
        ' RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
        ' LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
        Dim cat As String = "A Cheshire c" & "å" & "t"
        Dim loc As Integer = 0
        Dim scValues As StringComparison() =  { _
                        StringComparison.CurrentCulture, _
                        StringComparison.CurrentCultureIgnoreCase, _
                        StringComparison.InvariantCulture, _
                        StringComparison.InvariantCultureIgnoreCase, _
                        StringComparison.Ordinal, _
                        StringComparison.OrdinalIgnoreCase }
        Dim sc As StringComparison
        
        ' Clear the screen and display an introduction.
        Console.Clear()
        Console.WriteLine(intro)
        
        ' Display the current culture because culture affects the result. For example, 
        ' try this code example with the "sv-SE" (Swedish-Sweden) culture.
        Thread.CurrentThread.CurrentCulture = New CultureInfo("en-US")
        Console.WriteLine("The current culture is ""{0}"" - {1}.", _
                           Thread.CurrentThread.CurrentCulture.Name, _
                           Thread.CurrentThread.CurrentCulture.DisplayName)
        
        ' Display the string to search for and the string to search.
        Console.WriteLine("Search for the string ""{0}"" in the string ""{1}""", _
                           CapitalAWithRing, cat)
        Console.WriteLine()
        
        ' Note that in each of the following searches, we look for 
        ' LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains 
        ' LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates 
        ' the string was not found.
        ' Search using different values of StringComparsion. Specify the start 
        ' index and count. 
        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparsion. Specify the 
        ' start index. 
        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, cat.Length - 1, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparsion. 
        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.LastIndexOf(CapitalAWithRing, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
    
    End Sub
End Class

'
'Note: This code example was executed on a console whose user interface 
'culture is "en-US" (English-United States).
'
'This code example produces the following results:
'
'Find the last occurrence of a character using different values of StringComparison.
'The current culture is "en-US" - English (United States).
'Search for the string "Å" in the string "A Cheshire ca°t"
'
'Part 1: Start index and count are specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'
'Part 2: Start index is specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'
'Part 3: Neither start index nor count is specified.
'Comparison: CurrentCulture               Location:  -1
'Comparison: CurrentCultureIgnoreCase     Location:  12
'Comparison: InvariantCulture             Location:  -1
'Comparison: InvariantCultureIgnoreCase   Location:  12
'Comparison: Ordinal                      Location:  -1
'Comparison: OrdinalIgnoreCase            Location:  -1
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

搜尋 startIndex 會從字元位置開始,並繼續進行,直到 value 找到或已 count 檢查字元位置為止。The search begins at the startIndex character position and proceeds backward until either value is found or count character positions have been examined. 例如,如果 startIndexLength -1,則方法會搜尋 count 字串中最後一個字元的後置字元。For example, if startIndex is Length - 1, the method searches backward count characters from the last character in the string.

comparisonType參數指定要 value 使用下列參數來搜尋參數:The comparisonType parameter specifies to search for the value parameter using:

  • 目前或不變的文化特性。The current or invariant culture.
  • 區分大小寫或不區分大小寫的搜尋。A case-sensitive or case-insensitive search.
  • 單字或序數比較規則。Word or ordinal comparison rules.

給呼叫者的注意事項

字元集包含可忽略的字元,這些字元在執行語言或區分文化特性的比較時不列入考慮。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 執行區分文化特性的搜尋 (也就是說,如果 comparisonType 不是 OrdinalOrdinalIgnoreCase) 時,如果 value 包含可忽略的字元,則結果等於在已移除該字元的情況下搜尋。In a culture-sensitive search (that is, if comparisonType is not Ordinal or OrdinalIgnoreCase), if value contains an ignorable character, the result is equivalent to searching with that character removed.

在下列範例中, LastIndexOf(String, Int32, Int32, StringComparison) 方法是用來找出軟連字號的位置 (U + 00AD) 接著是 "m",在兩個字串中的最後一個字元位置之前的第一個字元位置。In the following example, the LastIndexOf(String, Int32, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" in all but the first character position before the final "m" in two strings. 只有其中一個字串包含必要的子字串。Only one of the strings contains the required substring. 如果範例是在 .NET Framework 4 或更新版本上執行,則在這兩種情況下,因為軟連字號是可忽略的字元,所以在執行區分文化特性的比較時,方法會傳回字串中 "m" 的索引。If the example is run on .NET Framework 4 or later, in both cases, because the soft hyphen is an ignorable character, the method returns the index of "m" in the string when it performs a culture-sensitive comparison. 不過,當它執行序數比較時,只會在第一個字串中尋找子字串。When it performs an ordinal comparison, however, it finds the substring only in the first string. 請注意,在第一個字串的案例中,包含軟連字號後接 "m",方法會在執行區分文化特性的比較時,傳回 "m" 的索引。Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method returns the index of the "m" when it performs a culture-sensitive comparison. 只有在執行序數比較時,方法才會傳回第一個字串中選擇性連字號的索引。The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

[!程式碼-csharpsystem.string. LastIndexOf # 24][! code-vbsystem.string. LastIndexOf # 24][!code-csharpSystem.String.LastIndexOf#24] [!code-vbSystem.String.LastIndexOf#24]

適用於

LastIndexOf(String, Int32)

回報這個執行個體中指定之字串最後一次出現時的所在索引 (以零為起始)。Reports the zero-based index position of the last occurrence of a specified string within this instance. 搜尋會從指定的字元位置開始,然後反向朝字串的開頭進行。The search starts at a specified character position and proceeds backward toward the beginning of the string.

public:
 int LastIndexOf(System::String ^ value, int startIndex);
public int LastIndexOf (string value, int startIndex);
member this.LastIndexOf : string * int -> int
Public Function LastIndexOf (value As String, startIndex As Integer) As Integer

參數

value
String

要搜尋的字串。The string to seek.

startIndex
Int32

搜尋開始位置。The search starting position. 搜尋會從 startIndex 朝這個執行個體的開頭進行。The search proceeds from startIndex toward the beginning of this instance.

傳回

Int32

如果找到該字串,則為 value 的以零為起始索引位置,如果找不到該字串或者目前的執行個體等於 Empty,則為 -1。The zero-based starting index position of value if that string is found, or -1 if it is not found or if the current instance equals Empty.

例外狀況

valuenullvalue is null.

目前的執行個體不等於 Empty,且 startIndex 小於零或大於目前執行個體的長度。The current instance does not equal Empty, and startIndex is less than zero or greater than the length of the current instance.

-或--or-

目前的執行個體等於 Empty,且 startIndex 小於 -1 或大於零。The current instance equals Empty, and startIndex is less than -1 or greater than zero.

範例

下列範例會尋找目標字串中所有出現之字串的索引,從目標字串的結尾開始,一直到目標字串的開頭。The following example finds the index of all occurrences of a string in target string, working from the end of the target string to the start of the target string.

// Sample for String::LastIndexOf(String, Int32)
using namespace System;
int main()
{
   String^ br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
   String^ br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
   String^ str = "Now is the time for all good men to come to the aid of their party.";
   int start;
   int at;
   start = str->Length - 1;
   Console::WriteLine( "All occurrences of 'he' from position {0} to 0.", start );
   Console::WriteLine( "{0}\n{1}\n{2}\n", br1, br2, str );
   Console::Write( "The string 'he' occurs at position(s): " );
   at = 0;
   while ( (start > -1) && (at > -1) )
   {
      at = str->LastIndexOf( "he", start );
      if ( at > -1 )
      {
         Console::Write( " {0} ", at );
         start = at - 1;
      }
   }

   Console::WriteLine();
}

/*
This example produces the following results:
All occurrences of 'he' from position 66 to 0.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The string 'he' occurs at position(s):  56  45  8
*/
// Sample for String.LastIndexOf(String, Int32)
using System;

class Sample {
    public static void Main() {

    string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
    string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
    string str = "Now is the time for all good men to come to the aid of their party.";
    int start;
    int at;

    start = str.Length-1;
    Console.WriteLine("All occurrences of 'he' from position {0} to 0.", start);
    Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str);
    Console.Write("The string 'he' occurs at position(s): ");

    at = 0;
    while((start > -1) && (at > -1))
        {
        at = str.LastIndexOf("he", start);
        if (at > -1)
            {
            Console.Write("{0} ", at);
            start = at - 1;
            }
        }
    Console.Write("{0}{0}{0}", Environment.NewLine);
    }
}
/*
This example produces the following results:
All occurrences of 'he' from position 66 to 0.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The string 'he' occurs at position(s): 56 45 8


*/
' Sample for String.LastIndexOf(String, Int32)
 _

Class Sample
   
   Public Shared Sub Main()
      
      Dim br1 As String = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-"
      Dim br2 As String = "0123456789012345678901234567890123456789012345678901234567890123456"
      Dim str As String = "Now is the time for all good men to come to the aid of their party."
      Dim start As Integer
      Dim at As Integer

      '#3
      start = str.Length - 1
      Console.WriteLine("All occurrences of 'he' from position {0} to 0.", start)
      Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str)
      Console.Write("The string 'he' occurs at position(s): ")
      
      at = 0
      While start > - 1 And at > - 1
         at = str.LastIndexOf("he", start)
         If at > - 1 Then
            Console.Write("{0} ", at)
            start = at - 1
         End If
      End While
      Console.Write("{0}{0}{0}", Environment.NewLine)
   End Sub
End Class
'
'This example produces the following results:
'All occurrences of 'he' from position 66 to 0.
'0----+----1----+----2----+----3----+----4----+----5----+----6----+-
'0123456789012345678901234567890123456789012345678901234567890123456
'Now is the time for all good men to come to the aid of their party.
'
'The string 'he' occurs at position(s): 56 45 8
'
'

備註

索引編號從零開始。Index numbering starts from zero. 也就是字串中的第一個字元是在索引零,最後一個字元是 Length -1。That is, the first character in the string is at index zero and the last is at Length - 1.

搜尋 startIndex 會從這個實例的字元位置開始,並在 value 找到任何一項或檢查第一個字元位置之前繼續往前移動。The search begins at the startIndex character position of this instance and proceeds backward toward the beginning until either value is found or the first character position has been examined. 例如,如果 startIndexLength -1,則方法會搜尋字串中最後一個字元到開頭的每個字元。For example, if startIndex is Length - 1, the method searches every character from the last character in the string to the beginning.

這個方法會使用目前的文化特性,執行文字 (區分大小寫且區分文化特性) 搜尋。This method performs a word (case-sensitive and culture-sensitive) search using the current culture.

字元集包含可忽略的字元,這些字元在執行語言或區分文化特性的比較時不列入考慮。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 執行區分文化特性的搜尋時,如果 value 包含可忽略的字元,則結果等於在已移除該字元的情況下搜尋。In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. 在下列範例中, LastIndexOf(String, Int32) 方法是用來尋找包含軟連字號 (U + 00AD) 的子字串,並在字串中之前或包含最後的 "m"。In the following example, the LastIndexOf(String, Int32) method is used to find a substring that includes a soft hyphen (U+00AD) and that precedes or includes the final "m" in a string. 如果範例是在 .NET Framework 4 或更新版本上執行,因為搜尋字串中的軟連字號會被忽略,呼叫方法以尋找包含軟連字號的子字串,而 "m" 則會傳回字串中 "m" 的位置,而將它呼叫以尋找包含軟連字號的子字串,而 "n" 會傳回 "n" 的位置。If the example is run on .NET Framework 4 or later, because the soft hyphen in the search string is ignored, calling the method to find a substring that consists of the soft hyphen and "m" returns the position of the "m" in the string, whereas calling it to find a substring that consists of the soft hyphen and "n" returns the position of the "n".

int position = 0;
string s1 = "ani\u00ADmal";
string s2 = "animal";

// Find the index of the soft hyphen followed by "n".
position = s1.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s1.LastIndexOf("\u00ADn", position));

position = s2.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s2.LastIndexOf("\u00ADn", position));

// Find the index of the soft hyphen followed by "m".
position = s1.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s1.LastIndexOf("\u00ADm", position));

position = s2.LastIndexOf("m");
Console.WriteLine($"'m' at position {position}");

if (position >= 0)
    Console.WriteLine(s2.LastIndexOf("\u00ADm", position));

// The example displays the following output:
//
// 'm' at position 4
// 1
// 'm' at position 3
// 1
// 'm' at position 4
// 4
// 'm' at position 3
// 3
Dim position As Integer
Dim softHyphen As String = ChrW(&HAD)
Dim s1 As String = "ani" + softHyphen + "mal"
Dim s2 As String = "animal"

' Find the index of the soft hyphen followed by "n".
position = s1.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s1.LastIndexOf(softHyphen + "n", position))
End If

position = s2.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s2.LastIndexOf(softHyphen + "n", position))
End If

' Find the index of the soft hyphen followed by "m".
position = s1.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s1.LastIndexOf(softHyphen + "m", position))
End If

position = s2.LastIndexOf("m")
Console.WriteLine($"'m' at position {position}")

If position >= 0 Then
    Console.WriteLine(s2.LastIndexOf(softHyphen + "m", position))
End If

' The example displays the following output:
'
' 'm' at position 4
' 1
' 'm' at position 3
' 1
' 'm' at position 4
' 4
' 'm' at position 3
' 3

給呼叫者的注意事項

使用字串的最佳做法中所述,我們建議您避免呼叫替代預設值的字串比較方法,而改為呼叫需要明確指定參數的方法。As explained in Best Practices for Using Strings, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. 若要使用目前文化特性的比較規則來尋找在特定字元位置之前的子字串的索引,請使用的值來呼叫方法多載,以做 LastIndexOf(String, Int32, StringComparison) CurrentCulture 為其參數的值 comparisonTypeTo find the index of a substring that precedes a particular character position by using the comparison rules of the current culture, call the LastIndexOf(String, Int32, StringComparison) method overload with a value of CurrentCulture for its comparisonType parameter.

另請參閱

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