String.IndexOf 方法

定义

报告指定 Unicode 字符或字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of a specified Unicode character or string within this instance. 如果未在此实例中找到该字符或字符串,则此方法返回 -1。The method returns -1 if the character or string is not found in this instance.

重载

IndexOf(String, Int32, Int32)

报告指定字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in this instance. 搜索从指定字符位置开始,并检查指定数量的字符位置。The search starts at a specified character position and examines a specified number of character positions.

IndexOf(String, Int32, Int32, StringComparison)

报告指定的字符串在当前 String 对象中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in the current String object. 参数指定当前字符串中的起始搜索位置、要搜索的当前字符串中的字符数量,以及要用于指定字符串的搜索类型。Parameters specify the starting search position in the current string, the number of characters in the current string to search, and the type of search to use for the specified string.

IndexOf(String, Int32, StringComparison)

报告指定的字符串在当前 String 对象中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in the current String object. 参数指定当前字符串中的起始搜索位置以及用于指定字符串的搜索类型。Parameters specify the starting search position in the current string and the type of search to use for the specified string.

IndexOf(Char, Int32, Int32)

报告指定字符在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified character in this instance. 搜索从指定字符位置开始,并检查指定数量的字符位置。The search starts at a specified character position and examines a specified number of character positions.

IndexOf(String, StringComparison)

报告指定的字符串在当前 String 对象中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in the current String object. 一个参数指定要用于指定字符串的搜索类型。A parameter specifies the type of search to use for the specified string.

IndexOf(Char, StringComparison)

报告指定 Unicode 字符在此字符串中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified Unicode character in this string. 一个参数指定要用于指定字符的搜索类型。A parameter specifies the type of search to use for the specified character.

IndexOf(Char, Int32)

报告指定 Unicode 字符在此字符串中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified Unicode character in this string. 该搜索从指定字符位置开始。The search starts at a specified character position.

IndexOf(String)

报告指定字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in this instance.

IndexOf(Char)

报告指定 Unicode 字符在此字符串中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified Unicode character in this string.

IndexOf(String, Int32)

报告指定字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in this instance. 该搜索从指定字符位置开始。The search starts at a specified character position.

IndexOf(String, Int32, Int32)

报告指定字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in this instance. 搜索从指定字符位置开始,并检查指定数量的字符位置。The search starts at a specified character position and examines a specified number of character positions.

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

参数

value
String

要搜寻的字符串。The string to seek.

startIndex
Int32

搜索起始位置。The search starting position.

count
Int32

要检查的字符位置数。The number of character positions to examine.

返回

如果找到该字符串,则为从当前实例的起始位置开始的从零开始的 value 的索引位置;否则为 -1。The zero-based index position of value from the start of the current instance if that string is found, or -1 if it is not. 如果 valueEmpty,则返回值为 startIndexIf value is Empty, the return value is startIndex.

异常

valuenullvalue is null.

countstartIndex 为负数。count or startIndex is negative.

-or- startIndex 大于此字符串的长度。startIndex is greater than the length of this string.

-or- count 大于此字符串的长度减 startIndexcount is greater than the length of this string minus startIndex.

示例

下面的示例查找字符串 "he" 在另一个字符串的子字符串中的所有匹配项的索引。The following example finds the index of all occurrences of the string "he" within a substring of another string. 请注意,必须为每个搜索迭代重新计算要搜索的字符数。Note that the number of characters to be searched must be recalculated for each search iteration.

// Sample for String::IndexOf(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 end;
   int count;
   end = str->Length;
   start = end / 2;
   Console::WriteLine();
   Console::WriteLine( "All occurrences of 'he' from position {0} to {1}.", start, end - 1 );
   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 <= end) && (at > -1) )
   {
      
      // start+count must be a position within -str-.
      count = end - start;
      at = str->IndexOf( "he", start, count );
      if ( at == -1 )
            break;

      Console::Write( "{0} ", at );
      start = at + 1;
   }

   Console::WriteLine();
}

/*
This example produces the following results:

All occurrences of 'he' from position 33 to 66.
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): 45 56

*/
string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+---";
string br2 = "012345678901234567890123456789012345678901234567890123456789012345678";
string str = "Now is the time for all good men to come to the aid of their country.";
int start;
int at;
int end;
int count;

end = str.Length;
start = end/2;
Console.WriteLine();
Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, end-1);
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 <= end) && (at > -1))
{
    // start+count must be a position within -str-.
    count = end - start;
    at = str.IndexOf("he", start, count);
    if (at == -1) break;
    Console.Write("{0} ", at);
    start = at+1;
}
Console.WriteLine();

/*
This example produces the following results:

All occurrences of 'he' from position 34 to 68.
0----+----1----+----2----+----3----+----4----+----5----+----6----+---
012345678901234567890123456789012345678901234567890123456789012345678
Now is the time for all good men to come to the aid of their country.

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

*/
' Sample for String.IndexOf(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 [end] As Integer
      Dim count As Integer
      
      [end] = str.Length
      start = [end] / 2
      Console.WriteLine()
      Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, [end] - 1)
      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 <= [end] AndAlso at > - 1
         ' start+count must be a position within -str-.
         count = [end] - start
         at = str.IndexOf("he", start, count)
         If at = - 1 Then
            Exit While
         End If
         Console.Write("{0} ", at)
         start = at + 1
      End While
      Console.WriteLine()
   End Sub
End Class
'
'This example produces the following results:
'
'All occurrences of 'he' from position 33 to 66.
'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): 45 56
'
'

注解

索引编号从0(零)开始。Index numbering starts from 0 (zero). startIndex 参数可以介于 0 到字符串实例的长度。The startIndex parameter can range from 0 to the length of the string instance.

此方法使用当前区域性执行 word (区分大小写和区分区域性的)搜索。This method performs a word (case-sensitive and culture-sensitive) search using the current culture. 搜索从 startIndex 开始,并继续 + count-1 startIndexThe search begins at startIndex and continues to startIndex + count -1. 搜索中不包括 startIndex + count 的字符。The character at startIndex + count is not included in the search.

字符集包括可忽略字符,在执行语言性的或区分区域性的比较时该字符不被考虑。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 在区分区域性的搜索中,如果 value 包含一个可忽略字符,则结果与移除了该字符的搜索等效。In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. 如果 value 只包含一个或多个可忽略字符,则 IndexOf(String, Int32, Int32) 方法始终返回 startIndex,这是搜索开始处的字符位置。If value consists only of one or more ignorable characters, the IndexOf(String, Int32, Int32) method always returns startIndex, which is the character position at which the search begins. 在下面的示例中,IndexOf(String, Int32, Int32) 方法用于查找软连字符(U + 00AD)后跟 "m" 的位置,该位置从两个字符串中的第三个到第六个字符位置开始。In the following example, the IndexOf(String, Int32, Int32) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting in the third through sixth character positions in two strings. 只有一个字符串包含必需的子字符串。Only one of the strings contains the required substring. 如果该示例在 .NET Framework 4.NET Framework 4 或更高版本上运行,则在这两种情况下,因为软连字符是可忽略字符,所以当执行区分区域性的比较时,该方法将返回字符串中的 "m" 的索引。If the example is run on the .NET Framework 4.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. 注意对于第一个字符串,包含软连字符后跟“m”,该方法无法返回该软连字符的索引,而是返回“m”的索引。Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m".

using System;

public class Example
{
    public static void Main()
    {
        string searchString = "\u00ADm";
        string s1 = "ani\u00ADmal" ;
        string s2 = "animal";

        Console.WriteLine(s1.IndexOf(searchString, 2, 4));
        Console.WriteLine(s2.IndexOf(searchString, 2, 4));

        // The example displays the following output:
        //       4
        //       3
    }
}
Module Example
   Public Sub Main()
      Dim searchString As String = Chrw(&h00AD) + "m"
      Dim s1 As String = "ani" + ChrW(&h00AD) + "mal"
      Dim s2 As String = "animal"

      Console.WriteLine(s1.IndexOf(searchString, 2, 4))
      Console.WriteLine(s2.IndexOf(searchString, 2, 4))
   End Sub
End Module
' The example displays the following output:
'       4
'       3

调用方说明

使用字符串的最佳做法中所述,建议你避免调用替换默认值的字符串比较方法,并改为调用需要显式指定参数的方法。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. 若要使用当前区域性的比较规则来执行此操作,请使用其 comparisonType 参数的值 CurrentCulture 调用 IndexOf(String, Int32, Int32, StringComparison) 方法重载。To use the comparison rules of the current culture to perform this operation, call the IndexOf(String, Int32, Int32, StringComparison) method overload with a value of CurrentCulture for its comparisonType parameter.

另请参阅

IndexOf(String, Int32, Int32, StringComparison)

报告指定的字符串在当前 String 对象中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in the current String object. 参数指定当前字符串中的起始搜索位置、要搜索的当前字符串中的字符数量,以及要用于指定字符串的搜索类型。Parameters specify the starting search position in the current string, the number of characters in the current string to search, and the type of search to use for the specified string.

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

参数

value
String

要搜寻的字符串。The string to seek.

startIndex
Int32

搜索起始位置。The search starting position.

count
Int32

要检查的字符位置数。The number of character positions to examine.

comparisonType
StringComparison

指定搜索规则的枚举值之一。One of the enumeration values that specifies the rules for the search.

返回

如果找到该字符串,则为从当前实例的起始位置开始的从零开始的 value 参数索引位置;否则为 -1。The zero-based index position of the value parameter from the start of the current instance if that string is found, or -1 if it is not. 如果 valueEmpty,则返回值为 startIndexIf value is Empty, the return value is startIndex.

异常

valuenullvalue is null.

countstartIndex 为负数。count or startIndex is negative.

-or- startIndex 大于此实例的长度。startIndex is greater than the length of this instance.

-or- count 大于此字符串的长度减 startIndexcount is greater than the length of this string minus startIndex.

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

示例

下面的示例演示 IndexOf 方法的三个重载,该方法使用 StringComparison 枚举的不同值在另一个字符串内查找字符串的第一个匹配项。The following example demonstrates three overloads of the IndexOf method that find the first occurrence of a string within another string using different values of the StringComparison enumeration.

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

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

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the first 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 StringComparison. Specify the start 
// index and count. 

    Console.WriteLine("Part 1: Start index and count are specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparison. Specify the 
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(CapitalAWithRing, 0, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparison. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(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 first 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.IndexOf(String, ..., StringComparison) methods.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the first 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 StringComparison. Specify the start 
        ' index and count.

        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparison. Specify the 
        ' start index. 

        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparison. 

        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(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 first 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
'

注解

索引编号从0(零)开始。Index numbering starts from 0 (zero). startIndex 参数可以介于 0 到字符串实例的长度。The startIndex parameter can range from 0 to the length of the string instance.

搜索从 startIndex 开始,并继续 + count-1 startIndexThe search begins at startIndex and continues to startIndex + count -1. 搜索中不包括 startIndex + count 的字符。The character at startIndex + count is not included in the search.

comparisonType 参数通过使用区分大小写或不区分大小写的搜索以及使用 word 或序号比较规则,指定搜索使用当前或固定区域性的 value 参数。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.

调用方说明

字符集包括可忽略字符,在执行语言性的或区分区域性的比较时该字符不被考虑。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 在区分区域性的搜索 (即,如果 comparisonType 不是 OrdinalOrdinalIgnoreCase) 中,如果 value 包含一个可忽略字符,则结果与移除了该字符的搜索等效。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. 如果 value 只包含一个或多个可忽略字符,则 IndexOf(String, Int32, Int32, StringComparison) 方法始终返回 startIndex,这是搜索开始处的字符位置。If value consists only of one or more ignorable characters, the IndexOf(String, Int32, Int32, StringComparison) method always returns startIndex, which is the character position at which the search begins.

在下面的示例中,IndexOf(String, Int32, Int32, StringComparison) 方法用于查找软连字符(U + 00AD)后跟 "m" 的位置,该位置从两个字符串中的第三个到第六个字符位置开始。In the following example, the IndexOf(String, Int32, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting in the third through sixth character positions in two strings. 只有一个字符串包含必需的子字符串。Only one of the strings contains the required substring. 如果该示例在 .NET Framework 4.NET Framework 4 或更高版本上运行,则在这两种情况下,因为软连字符是可忽略字符,所以当执行区分区域性的比较时,该方法将返回字符串中的 "m" 的索引。If the example is run on the .NET Framework 4.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. 但当它执行序号比较时,它只查找第一个字符串中的子字符串。When it performs an ordinal comparison, however, it finds the substring only in the first string. 请注意,对于包含软连字符后跟 "m" 的软连字符的第一个字符串,该方法将无法返回软连字符的索引,而是在执行区分区域性的比较时返回 "m" 的索引。Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m" when it performs a culture-sensitive comparison. 只有当此方法执行序号比较时,它才会在第一个字符串中返回软连字符的索引。The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

[!code-csharpSystem.String.IndexOf#24] [!code-vbSystem.String.IndexOf#24][!code-csharpSystem.String.IndexOf#24] [!code-vbSystem.String.IndexOf#24]

IndexOf(String, Int32, StringComparison)

报告指定的字符串在当前 String 对象中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in the current String object. 参数指定当前字符串中的起始搜索位置以及用于指定字符串的搜索类型。Parameters specify the starting search position in the current string and the type of search to use for the specified string.

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

参数

value
String

要搜寻的字符串。The string to seek.

startIndex
Int32

搜索起始位置。The search starting position.

comparisonType
StringComparison

指定搜索规则的枚举值之一。One of the enumeration values that specifies the rules for the search.

返回

如果找到该字符串,则为从当前实例的起始位置开始的从零开始的 value 参数索引位置;否则为 -1。The zero-based index position of the value parameter from the start of the current instance if that string is found, or -1 if it is not. 如果 valueEmpty,则返回值为 startIndexIf value is Empty, the return value is startIndex.

异常

valuenullvalue is null.

startIndex 小于 0(零)或大于此字符串的长度。startIndex is less than 0 (zero) or greater than the length of this string.

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

示例

下面的示例演示 IndexOf 方法的三个重载,该方法使用 StringComparison 枚举的不同值在另一个字符串内查找字符串的第一个匹配项。The following example demonstrates three overloads of the IndexOf method that find the first occurrence of a string within another string using different values of the StringComparison enumeration.

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

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

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the first 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 StringComparison. Specify the start 
// index and count. 

    Console.WriteLine("Part 1: Start index and count are specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparison. Specify the 
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(CapitalAWithRing, 0, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparison. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(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 first 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.IndexOf(String, ..., StringComparison) methods.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the first 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 StringComparison. Specify the start 
        ' index and count.

        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparison. Specify the 
        ' start index. 

        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparison. 

        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(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 first 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
'

注解

索引编号从0开始。Index numbering starts from 0. startIndex 参数可以介于 0 到字符串实例的长度。The startIndex parameter can range from 0 to the length of the string instance. 如果 startIndex 等于字符串实例的长度,则该方法将返回-1。If startIndex equals the length of the string instance, the method returns -1.

comparisonType 参数通过使用区分大小写或不区分大小写的搜索以及使用 word 或序号比较规则,指定搜索使用当前或固定区域性的 value 参数。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.

调用方说明

字符集包括可忽略字符,在执行语言性的或区分区域性的比较时该字符不被考虑。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 在区分区域性的搜索 (即,如果 comparisonType 不是 OrdinalOrdinalIgnoreCase) 中,如果 value 包含一个可忽略字符,则结果与移除了该字符的搜索等效。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. 如果 value 只包含一个或多个可忽略字符,则 IndexOf(String, Int32, StringComparison) 方法始终返回 startIndex,这是搜索开始处的字符位置。If value consists only of one or more ignorable characters, the IndexOf(String, Int32, StringComparison) method always returns startIndex, which is the character position at which the search begins.

在下面的示例中,IndexOf(String, Int32, StringComparison) 方法用于查找软连字符(U + 00AD)后跟 "m" 的位置(从两个字符串中的第三个字符位置开始)。In the following example, the IndexOf(String, Int32, StringComparison) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting with the third character position in two strings. 只有一个字符串包含所需的子字符串。如果该示例在 .NET Framework 4.NET Framework 4 或更高版本上运行,则在这两种情况下,因为软连字符是可忽略字符,所以当执行区分区域性的比较时,该方法将返回字符串中的 "m" 的索引。Only one of the strings contains the required substring.If the example is run on the .NET Framework 4.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. 注意对于第一个字符串,包含软连字符后跟“m”,该方法无法返回该软连字符的索引,而是返回“m”的索引。Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m". 只有当此方法执行序号比较时,它才会在第一个字符串中返回软连字符的索引。The method returns the index of the soft hyphen in the first string only when it performs an ordinal comparison.

[!code-csharpSystem.String.IndexOf#25] [!code-vbSystem.String.IndexOf#25][!code-csharpSystem.String.IndexOf#25] [!code-vbSystem.String.IndexOf#25]

IndexOf(Char, Int32, Int32)

报告指定字符在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified character in this instance. 搜索从指定字符位置开始,并检查指定数量的字符位置。The search starts at a specified character position and examines a specified number of character positions.

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

参数

value
Char

要查找的 Unicode 字符。A Unicode character to seek.

startIndex
Int32

搜索起始位置。The search starting position.

count
Int32

要检查的字符位置数。The number of character positions to examine.

返回

如果找到该字符,则为从字符串的起始位置开始的 value 从零开始的索引位置;否则为 -1。The zero-based index position of value from the start of the string if that character is found, or -1 if it is not.

异常

countstartIndex 为负数。count or startIndex is negative.

-or- startIndex 大于此字符串的长度。startIndex is greater than the length of this string.

-or- count 大于此字符串的长度减 startIndexcount is greater than the length of this string minus startIndex.

示例

下面的示例演示 IndexOf 方法。The following example demonstrates the IndexOf method.

// Example for the String::IndexOf( Char, int, int ) method.
using namespace System;
void FindAllChar( Char target, String^ searched )
{
   Console::Write( "The character '{0}' occurs at position(s): ", target );
   int startIndex = -1;
   int hitCount = 0;
   
   // Search for all occurrences of the target.
   while ( true )
   {
      startIndex = searched->IndexOf( target, startIndex + 1, searched->Length - startIndex - 1 );
      
      // Exit the loop if the target is not found.
      if ( startIndex < 0 )
            break;

      Console::Write( "{0}, ", startIndex );
      hitCount++;
   }

   Console::WriteLine( "occurrences: {0}", hitCount );
}

int main()
{
   String^ br1 = "0----+----1----+----2----+----3----+----"
   "4----+----5----+----6----+----7";
   String^ br2 = "0123456789012345678901234567890123456789"
   "0123456789012345678901234567890";
   String^ str = "ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi "
   "ABCDEFGHI abcdefghi ABCDEFGHI";
   Console::WriteLine( "This example of String::IndexOf( Char, int, int )\n"
   "generates the following output." );
   Console::WriteLine( "{0}{1}{0}{2}{0}{3}{0}", Environment::NewLine, br1, br2, str );
   FindAllChar( 'A', str );
   FindAllChar( 'a', str );
   FindAllChar( 'I', str );
   FindAllChar( 'i', str );
   FindAllChar( '@', str );
   FindAllChar( ' ', str );
}

/*
This example of String::IndexOf( Char, int, int )
generates the following output.

0----+----1----+----2----+----3----+----4----+----5----+----6----+----7
01234567890123456789012345678901234567890123456789012345678901234567890
ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI

The character 'A' occurs at position(s): 0, 20, 40, 60, occurrences: 4
The character 'a' occurs at position(s): 10, 30, 50, occurrences: 3
The character 'I' occurs at position(s): 8, 28, 48, 68, occurrences: 4
The character 'i' occurs at position(s): 18, 38, 58, occurrences: 3
The character '@' occurs at position(s): occurrences: 0
The character ' ' occurs at position(s): 9, 19, 29, 39, 49, 59, occurrences: 6
*/
// Example for the String.IndexOf( char, int, int ) method.
using System;

class IndexOfCII 
{
    public static void Main() 
    {
        string br1 = 
            "0----+----1----+----2----+----3----+----" +
            "4----+----5----+----6----+----7";
        string br2 = 
            "0123456789012345678901234567890123456789" +
            "0123456789012345678901234567890";
        string str = 
            "ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi " +
            "ABCDEFGHI abcdefghi ABCDEFGHI";

        Console.WriteLine( 
            "This example of String.IndexOf( char, int, int )\n" +
            "generates the following output." );
        Console.WriteLine( 
            "{0}{1}{0}{2}{0}{3}{0}", 
            Environment.NewLine, br1, br2, str );

        FindAllChar( 'A', str );
        FindAllChar( 'a', str );
        FindAllChar( 'I', str );
        FindAllChar( 'i', str );
        FindAllChar( '@', str );
        FindAllChar( ' ', str );
    }

    static void FindAllChar( Char target, String searched )
    {
        Console.Write( 
            "The character '{0}' occurs at position(s): ", 
            target );

        int     startIndex = -1;
        int     hitCount = 0;

        // Search for all occurrences of the target.
        while( true )
        {
            startIndex = searched.IndexOf( 
                target, startIndex + 1, 
                searched.Length - startIndex - 1 );

            // Exit the loop if the target is not found.
            if( startIndex < 0 )
                break;

            Console.Write( "{0}, ", startIndex );
            hitCount++;
        }

        Console.WriteLine( "occurrences: {0}", hitCount );
    }
}

/*
This example of String.IndexOf( char, int, int )
generates the following output.

0----+----1----+----2----+----3----+----4----+----5----+----6----+----7
01234567890123456789012345678901234567890123456789012345678901234567890
ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI

The character 'A' occurs at position(s): 0, 20, 40, 60, occurrences: 4
The character 'a' occurs at position(s): 10, 30, 50, occurrences: 3
The character 'I' occurs at position(s): 8, 28, 48, 68, occurrences: 4
The character 'i' occurs at position(s): 18, 38, 58, occurrences: 3
The character '@' occurs at position(s): occurrences: 0
The character ' ' occurs at position(s): 9, 19, 29, 39, 49, 59, occurrences: 6
*/
' Example for the String.IndexOf( Char, Integer, Integer ) method.
Module IndexOfCII
   
    Sub Main()
        Dim br1 As String = _
            "0----+----1----+----2----+----3----+----" & _
            "4----+----5----+----6----+----7"
        Dim br2 As String = _
            "0123456789012345678901234567890123456789" & _
            "0123456789012345678901234567890"
        Dim str As String = _
            "ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi " & _
            "ABCDEFGHI abcdefghi ABCDEFGHI"
          
        Console.WriteLine( _
            "This example of String.IndexOf( Char, Integer, Integer )" & _
            vbCrLf & "generates the following output." )
        Console.WriteLine( _
            "{0}{1}{0}{2}{0}{3}{0}", _
            Environment.NewLine, br1, br2, str)

        FindAllChar("A"c, str)
        FindAllChar("a"c, str)
        FindAllChar("I"c, str)
        FindAllChar("i"c, str)
        FindAllChar("@"c, str)
        FindAllChar(" "c, str)
    End Sub
       
    Sub FindAllChar(target As Char, searched As String)

        Console.Write( _
            "The character ""{0}"" occurs at position(s): ", target)
          
        Dim startIndex As Integer = - 1
        Dim hitCount As Integer = 0
          
        ' Search for all occurrences of the target.
        While True
            startIndex = searched.IndexOf( _
                target, startIndex + 1, _
                searched.Length - startIndex - 1)

            ' Exit the loop if the target is not found.
            If startIndex < 0 Then
                Exit While
            End If 

            Console.Write("{0}, ", startIndex)
            hitCount += 1
        End While
          
        Console.WriteLine("occurrences: {0}", hitCount)

    End Sub
End Module 'IndexOfCII

' This example of String.IndexOf( Char, Integer, Integer )
' generates the following output.
' 
' 0----+----1----+----2----+----3----+----4----+----5----+----6----+----7
' 01234567890123456789012345678901234567890123456789012345678901234567890
' ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI
' 
' The character "A" occurs at position(s): 0, 20, 40, 60, occurrences: 4
' The character "a" occurs at position(s): 10, 30, 50, occurrences: 3
' The character "I" occurs at position(s): 8, 28, 48, 68, occurrences: 4
' The character "i" occurs at position(s): 18, 38, 58, occurrences: 3
' The character "@" occurs at position(s): occurrences: 0
' The character " " occurs at position(s): 9, 19, 29, 39, 49, 59, occurrences: 6

注解

搜索从 startIndex 开始,并继续 + count-1 startIndexThe search begins at startIndex and continues to startIndex + count -1. 搜索中不包括 startIndex + count 的字符。The character at startIndex + count is not included in the search.

索引编号从0(零)开始。Index numbering starts from 0 (zero). startIndex 参数可以介于 0 到字符串实例的长度。The startIndex parameter can range from 0 to the length of the string instance.

此方法执行序号(不区分区域性)搜索,其中,仅当字符的 Unicode 标量值相同时,才将其视为等效于另一个字符。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. 若要执行区分区域性的搜索,请使用 CompareInfo.IndexOf 方法,其中表示预构成字符的 Unicode 标量值(如连字 "Æ" (U + 00C6))可能被视为与正确序列,如 "AE" (U + 0041,U + 0045),具体取决于区域性。To perform a culture-sensitive search, use the CompareInfo.IndexOf 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.

另请参阅

IndexOf(String, StringComparison)

报告指定的字符串在当前 String 对象中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in the current String object. 一个参数指定要用于指定字符串的搜索类型。A parameter specifies the type of search to use for the specified string.

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

参数

value
String

要搜寻的字符串。The string to seek.

comparisonType
StringComparison

指定搜索规则的枚举值之一。One of the enumeration values that specifies the rules for the search.

返回

如果找到该字符串,则为 value 参数的索引位置;如果未找到该字符串,则为 -1。The index position of the value parameter if that string is found, or -1 if it is not. 如果 valueEmpty,则返回值为 0。If value is Empty, the return value is 0.

异常

valuenullvalue is null.

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

示例

下面的示例演示 IndexOf 方法的三个重载,该方法使用 StringComparison 枚举的不同值在另一个字符串内查找字符串的第一个匹配项。The following example demonstrates three overloads of the IndexOf method that find the first occurrence of a string within another string using different values of the StringComparison enumeration.

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

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

class Sample 
{
    public static void Main() 
    {
    string intro = "Find the first 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 StringComparison. Specify the start 
// index and count. 

    Console.WriteLine("Part 1: Start index and count are specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparison. Specify the 
// start index. 
    Console.WriteLine("\nPart 2: Start index is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(CapitalAWithRing, 0, sc);
        Console.WriteLine(resultFmt, sc, loc);
        }

// Search using different values of StringComparison. 
    Console.WriteLine("\nPart 3: Neither start index nor count is specified.");
    foreach (StringComparison sc in scValues)
        {
        loc = cat.IndexOf(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 first 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.IndexOf(String, ..., StringComparison) methods.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim intro As String = "Find the first 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 StringComparison. Specify the start 
        ' index and count.

        Console.WriteLine("Part 1: Start index and count are specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparison. Specify the 
        ' start index. 

        Console.WriteLine(vbCrLf & "Part 2: Start index is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(CapitalAWithRing, 0, sc)
            Console.WriteLine(resultFmt, sc, loc)
        Next sc
        
        ' Search using different values of StringComparison. 

        Console.WriteLine(vbCrLf & "Part 3: Neither start index nor count is specified.")
        For Each sc In  scValues
            loc = cat.IndexOf(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 first 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
'

注解

索引编号从0开始。Index numbering starts from zero.

comparisonType 参数通过使用区分大小写或不区分大小写的搜索以及使用 word 或序号比较规则,指定搜索使用当前或固定区域性的 value 参数。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.

调用方说明

字符集包括可忽略字符,在执行语言性的或区分区域性的比较时该字符不被考虑。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 在区分区域性的搜索 (即,如果 comparisonType 不是 OrdinalOrdinalIgnoreCase) 中,如果 value 包含一个可忽略字符,则结果与移除了该字符的搜索等效。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. 如果 value 只包含一个或多个可忽略字符,则 IndexOf(String, StringComparison) 方法始终返回0(零),指示在当前实例的开头找到匹配项。If value consists only of one or more ignorable characters, the IndexOf(String, StringComparison) method always returns 0 (zero) to indicate that the match is found at the beginning of the current instance.

在下面的示例中,IndexOf(String, StringComparison) 方法用于查找两个字符串中的三个子字符串(软连字符(U + 00AD)、软连字符后跟 "n" 和软连字符后跟 "m"。In the following example, the IndexOf(String, StringComparison) method is used to find three substrings (a soft hyphen (U+00AD), a soft hyphen followed by "n", and a soft hyphen followed by "m") in two strings. 只有一个字符串包含软连字符。Only one of the strings contains a soft hyphen. 如果该示例在 .NET Framework 4.NET Framework 4 或更高版本上运行,因为软连字符是可忽略的字符,所以区分区域性的搜索返回的值与在搜索字符串中未包含软连字符时返回的值相同。If the example is run on the .NET Framework 4.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. 不过,序号搜索成功地在一个字符串中查找软连字符,并报告从第二个字符串中缺少它。An ordinal search, however, successfully finds the soft hyphen in one string and reports that it is absent from the second string.

[!code-csharpSystem.String.IndexOf#26] [!code-vbSystem.String.IndexOf#26][!code-csharpSystem.String.IndexOf#26] [!code-vbSystem.String.IndexOf#26]

IndexOf(Char, StringComparison)

报告指定 Unicode 字符在此字符串中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified Unicode character in this string. 一个参数指定要用于指定字符的搜索类型。A parameter specifies the type of search to use for the specified character.

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

参数

value
Char

要查找的字符。The character to seek.

comparisonType
StringComparison

指定搜索规则的枚举值。An enumeration value that specifies the rules for the search.

返回

如果找到该字符,则为 value 的从零开始的索引位置;如果未找到,则为 -1。The zero-based index of value if that character is found, or -1 if it is not.

异常

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

注解

索引编号从0开始。Index numbering starts from zero.

comparisonType 参数是一个 StringComparison 枚举成员,该成员指定对 value 参数的搜索是使用当前还是固定的区域性,区分大小写或不区分大小写,或者使用单词或序号比较规则。The comparisonType parameter is a StringComparison enumeration member that specifies whether the search for the value argument uses the current or invariant culture, is case-sensitive or case-insensitive, or uses word or ordinal comparison rules.

IndexOf(Char, Int32)

报告指定 Unicode 字符在此字符串中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified Unicode character in this string. 该搜索从指定字符位置开始。The search starts at a specified character position.

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

参数

value
Char

要查找的 Unicode 字符。A Unicode character to seek.

startIndex
Int32

搜索起始位置。The search starting position.

返回

如果找到该字符,则为从字符串的起始位置开始的 value 从零开始的索引位置;否则为 -1。The zero-based index position of value from the start of the string if that character is found, or -1 if it is not.

异常

startIndex 小于 0(零)或大于此字符串的长度。startIndex is less than 0 (zero) or greater than the length of the string.

示例

下面的示例演示 IndexOf 方法。The following example demonstrates the IndexOf method.

// Sample for String::IndexOf(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;
   Console::WriteLine();
   Console::WriteLine( "All occurrences of 't' from position 0 to {0}.", str->Length - 1 );
   Console::WriteLine( "{1}{0}{2}{0}{3}{0}", Environment::NewLine, br1, br2, str );
   Console::Write( "The letter 't' occurs at position(s): " );
   at = 0;
   start = 0;
   while ( (start < str->Length) && (at > -1) )
   {
      at = str->IndexOf( 't', start );
      if ( at == -1 )
            break;

      Console::Write( "{0} ", at );
      start = at + 1;
   }

   Console::WriteLine();
}

/*
This example produces the following results:

All occurrences of 't' from position 0 to 66.
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): 7 11 33 41 44 55 64

*/
string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+---";
string br2 = "012345678901234567890123456789012345678901234567890123456789012345678";
string str = "Now is the time for all good men to come to the aid of their country.";
int start;
int at;

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

at = 0;
start = 0; 
while((start < str.Length) && (at > -1))
{
    at = str.IndexOf('t', start);
    if (at == -1) break;
    Console.Write("{0} ", at);
    start = at+1;
}
Console.WriteLine();

/*
This example produces the following results:

All occurrences of 't' from position 0 to 68.
0----+----1----+----2----+----3----+----4----+----5----+----6----+---
012345678901234567890123456789012345678901234567890123456789012345678
Now is the time for all good men to come to the aid of their country.

The letter 't' occurs at position(s): 7 11 33 41 44 55 65

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

Module Sample
    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

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

        at = 0
        start = 0
        While start < str.Length AndAlso at > -1
            at = str.IndexOf("t"c, start)
            If at = -1 Then
                Exit While
            End If
            Console.Write("{0} ", at)
            start = at + 1
        End While
        Console.WriteLine()
    End Sub
End Module
'
'This example produces the following results:
'
'All occurrences of 't' from position 0 to 66.
'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): 7 11 33 41 44 55 64
'
'

注解

索引编号从0开始。Index numbering starts from 0. startIndex 参数可以介于 0 到字符串实例的长度。The startIndex parameter can range from 0 to the length of the string instance. 如果 startIndex 等于字符串实例的长度,则该方法将返回-1。If startIndex equals the length of the string instance, the method returns -1.

搜索范围从 startIndex 到字符串的末尾。The search ranges from startIndex to the end of the string.

此方法执行序号(不区分区域性)搜索,其中,仅当字符的 Unicode 标量值相同时,才将其视为等效于另一个字符。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. 若要执行区分区域性的搜索,请使用 CompareInfo.IndexOf 方法,其中表示预构成字符的 Unicode 标量值(如连字 "Æ" (U + 00C6))可能被视为与正确序列,如 "AE" (U + 0041,U + 0045),具体取决于区域性。To perform a culture-sensitive search, use the CompareInfo.IndexOf 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.

另请参阅

IndexOf(String)

报告指定字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in this instance.

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

参数

value
String

要搜寻的字符串。The string to seek.

返回

如果找到该字符串,则为 value 的从零开始的索引位置;如果未找到该字符串,则为 -1。The zero-based index position of value if that string is found, or -1 if it is not. 如果 valueEmpty,则返回值为 0。If value is Empty, the return value is 0.

异常

valuenullvalue is null.

示例

下面的示例在 "动物" 中搜索 "n"。The following example searches for the "n" in "animal". 由于字符串索引从零开始,而不是从零开始,因此 IndexOf(String) 方法指示 "n" 位于位置1。Because string indexes begin at zero rather than one, the IndexOf(String) method indicates that the "n" is at position 1.

using namespace System;

void main()
{
   String^ str = "animal";
   String^ toFind = "n";
   int index = str->IndexOf("n");
   Console::WriteLine("Found '{0}' in '{1}' at position {2}",
                        toFind, str, index);

}
// The example displays the following output:
//        Found 'n' in 'animal' at position 1
String str = "animal";
String toFind = "n";
int index = str.IndexOf("n");
Console.WriteLine("Found '{0}' in '{1}' at position {2}",
                toFind, str, index);

// The example displays the following output:
//        Found 'n' in 'animal' at position 1
Public Module Example
   Public Sub Main()
      Dim str As String = "animal"
      Dim toFind As String = "n"
      Dim index As Integer = str.IndexOf("n")
      Console.WriteLine("Found '{0}' in '{1}' at position {2}",
                        toFind, str, index)
   End Sub
End Module
' The example displays the following output:
'       Found 'n' in 'animal' at position 1

下面的示例使用 IndexOf 方法来确定某一句子中动物名称的起始位置。The following example uses the IndexOf method to determine the starting position of an animal name in a sentence. 然后,它将使用此位置插入描述动物的形容词。It then uses this position to insert an adjective that describes the animal into the sentence.

using namespace System;

int main()
{
   String^ animal1 = "fox";
   String^ animal2 = "dog";
   String^ strTarget = String::Format( "The {0} jumps over the {1}.", animal1, animal2 );
   Console::WriteLine( "The original string is:{0}{1}{0}", Environment::NewLine, strTarget );
   Console::Write( "Enter an adjective (or group of adjectives) to describe the {0}: ==> ", animal1 );
   String^ adj1 = Console::ReadLine();
   Console::Write( "Enter an adjective (or group of adjectives) to describe the {0}: ==> ", animal2 );
   String^ adj2 = Console::ReadLine();
   adj1 = String::Concat( adj1->Trim(), " " );
   adj2 = String::Concat( adj2->Trim(), " " );
   strTarget = strTarget->Insert( strTarget->IndexOf( animal1 ), adj1 );
   strTarget = strTarget->Insert( strTarget->IndexOf( animal2 ), adj2 );
   Console::WriteLine( " {0}The final string is: {0} {1}", Environment::NewLine, strTarget );
}
// Output from the example might appear as follows:
//       The original string is:
//       The fox jumps over the dog.
//       
//       Enter an adjective (or group of adjectives) to describe the fox: ==> bold
//       Enter an adjective (or group of adjectives) to describe the dog: ==> lazy
//       
//       The final string is:
//       The bold fox jumps over the lazy dog.
using System;

public class Example {
    public static void Main() 
    {
        string animal1 = "fox";
        string animal2 = "dog";

        string strTarget = String.Format("The {0} jumps over the {1}.", 
                                         animal1, animal2);

        Console.WriteLine("The original string is:{0}{1}{0}", 
                          Environment.NewLine, strTarget);

        Console.Write("Enter an adjective (or group of adjectives) " +
                      "to describe the {0}: ==> ", animal1);
        string adj1 = Console.ReadLine();

        Console.Write("Enter an adjective (or group of adjectives) " + 
                      "to describe the {0}: ==> ", animal2);    
        string adj2 = Console.ReadLine();

        adj1 = adj1.Trim() + " ";
        adj2 = adj2.Trim() + " ";

        strTarget = strTarget.Insert(strTarget.IndexOf(animal1), adj1);
        strTarget = strTarget.Insert(strTarget.IndexOf(animal2), adj2);

        Console.WriteLine("{0}The final string is:{0}{1}", 
                          Environment.NewLine, strTarget);
    }
}
// Output from the example might appear as follows:
//       The original string is:
//       The fox jumps over the dog.
//       
//       Enter an adjective (or group of adjectives) to describe the fox: ==> bold
//       Enter an adjective (or group of adjectives) to describe the dog: ==> lazy
//       
//       The final string is:
//       The bold fox jumps over the lazy dog.
Public Class Example
    Public Shared Sub Main()
        Dim animal1 As String = "fox"
        Dim animal2 As String = "dog"
        Dim strTarget As String = String.Format("The {0} jumps over the {1}.", 
                                                animal1, animal2)
        
        Console.WriteLine("The original string is: {0}{1}{0}", 
                          Environment.NewLine, strTarget)
        
        Console.Write("Enter an adjective (or group of adjectives) " +
                      "to describe the {0}: ==> ", animal1)
        Dim adj1 As String = Console.ReadLine()
        
        Console.Write("Enter an adjective (or group of adjectives) " + 
                      "to describe the {0}: ==> ", animal2)
        Dim adj2 As String = Console.ReadLine()
        
        adj1 = adj1.Trim() + " "
        adj2 = adj2.Trim() + " "
        
        strTarget = strTarget.Insert(strTarget.IndexOf(animal1), adj1)
        strTarget = strTarget.Insert(strTarget.IndexOf(animal2), adj2)
        
        Console.WriteLine("{0}The final string is:{0}{1}", 
                          Environment.NewLine, strTarget)
    End Sub 
End Class 
' Output from the example might appear as follows:
'       The original string is:
'       The fox jumps over the dog.
'       
'       Enter an adjective (or group of adjectives) to describe the fox: ==> bold
'       Enter an adjective (or group of adjectives) to describe the dog: ==> lazy
'       
'       The final string is:
'       The bold fox jumps over the lazy dog.

注解

索引编号从0开始。Index numbering starts from zero.

此方法使用当前区域性执行 word (区分大小写和区分区域性的)搜索。This method performs a word (case-sensitive and culture-sensitive) search using the current culture. 搜索从该实例的第一个字符位置开始,并继续到最后一个字符的位置。The search begins at the first character position of this instance and continues until the last character position.

字符集包括可忽略字符,在执行语言性的或区分区域性的比较时该字符不被考虑。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 在区分区域性的搜索中,如果 value 包含一个可忽略字符,则结果与移除了该字符的搜索等效。In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. 如果 value 只包含一个或多个可忽略字符,则 IndexOf(String) 方法始终返回0(零),指示在当前实例的开头找到匹配项。If value consists only of one or more ignorable characters, the IndexOf(String) method always returns 0 (zero) to indicate that the match is found at the beginning of the current instance. 在下面的示例中,IndexOf(String) 方法用于查找两个字符串中的三个子字符串(软连字符(U + 00AD)、软连字符后跟 "n" 和软连字符后跟 "m"。In the following example, the IndexOf(String) method is used to find three substrings (a soft hyphen (U+00AD), a soft hyphen followed by "n", and a soft hyphen followed by "m") in two strings. 只有一个字符串包含软连字符。Only one of the strings contains a soft hyphen. 如果该示例在 .NET Framework 4.NET Framework 4 或更高版本上运行,则在每种情况下,因为软连字符是可忽略字符,所以结果与 value中未包含软连字符的结果相同。If the example is run on the .NET Framework 4.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. 仅搜索软连字符时,该方法返回0(零),指示它已在字符串的开头找到匹配项。When searching for a soft hyphen only, the method returns 0 (zero) to indicate that it has found a match at the beginning of the string.

using System;

public class Example
{
    public static void Main()
    {
        string s1 = "ani\u00ADmal";
        string s2 = "animal";
      
        // Find the index of the soft hyphen.
        Console.WriteLine(s1.IndexOf("\u00AD"));
        Console.WriteLine(s2.IndexOf("\u00AD"));
      
        // Find the index of the soft hyphen followed by "n".
        Console.WriteLine(s1.IndexOf("\u00ADn"));
        Console.WriteLine(s2.IndexOf("\u00ADn"));
      
        // Find the index of the soft hyphen followed by "m".
        Console.WriteLine(s1.IndexOf("\u00ADm"));
        Console.WriteLine(s2.IndexOf("\u00ADm"));

        // The example displays the following output
        // if run under the .NET Framework 4 or later:
        //       0
        //       0
        //       1
        //       1
        //       4
        //       3
    }
}
Module Example
   Public Sub Main()
      Dim softHyphen As String = ChrW(&h00AD)
      Dim s1 As String = "ani" + softHyphen + "mal"
      Dim s2 As String = "animal"
      
      ' Find the index of the soft hyphen.
      Console.WriteLine(s1.IndexOf(softHyphen))
      Console.WriteLine(s2.IndexOf(softHyphen))
      
      ' Find the index of the soft hyphen followed by "n".
      Console.WriteLine(s1.IndexOf(softHyphen + "n"))
      Console.WriteLine(s2.IndexOf(softHyphen + "n"))
      
      ' Find the index of the soft hyphen followed by "m".
      Console.WriteLine(s1.IndexOf(softHyphen + "m"))
      Console.WriteLine(s2.IndexOf(softHyphen + "m"))
   End Sub
End Module
' The example displays the following output 
' if run under the .NET Framework 4 or later:
'       0
'       0
'       1
'       1
'       4
'       3

调用方说明

使用字符串的最佳做法中所述,建议你避免调用替换默认值的字符串比较方法,并改为调用需要显式指定参数的方法。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. 若要使用当前区域性的比较规则查找字符串实例内子字符串的第一个索引,请使用其 comparisonType 参数的值 CurrentCulture 调用 IndexOf(String, StringComparison) 方法重载。To find the first index of a substring within a string instance by using the comparison rules of the current culture, call the IndexOf(String, StringComparison) method overload with a value of CurrentCulture for its comparisonType parameter.

另请参阅

IndexOf(Char)

报告指定 Unicode 字符在此字符串中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified Unicode character in this string.

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

参数

value
Char

要查找的 Unicode 字符。A Unicode character to seek.

返回

如果找到该字符,则为 value 的从零开始的索引位置;如果未找到,则为 -1。The zero-based index position of value if that character is found, or -1 if it is not.

示例

下面的示例演示如何使用 IndexOf 方法搜索某个字符的 StringThe following example demonstrates how you can search a String for a character using the IndexOf method.

using namespace System;

void main()
{
   // Create a Unicode String with 5 Greek Alpha characters.
   String^ szGreekAlpha = gcnew String(L'\x0391',5);

   // Create a Unicode String with a 3 Greek Omega characters.
   String^ szGreekOmega = L"\x03A9\x03A9\x03A9";

   String^ szGreekLetters = String::Concat(szGreekOmega, szGreekAlpha, 
                                           szGreekOmega->Clone());

   // Display the entire string.
   Console::WriteLine(szGreekLetters);

   // The first index of Alpha.
   int ialpha = szGreekLetters->IndexOf( L'\x0391');
   // The first index of Omega.
   int iomega = szGreekLetters->IndexOf(L'\x03A9');

   Console::WriteLine("First occurrence of the Greek letter Alpha: Index {0}", 
                      ialpha);
   Console::WriteLine("First occurrence of the Greek letter Omega: Index {0}", 
                      iomega);
}
// The example displays the following output:
//       The string: OOO?????OOO
//       First occurrence of the Greek letter Alpha: Index 3
//       First occurrence of the Greek letter Omega: Index 0
// Create a Unicode string with 5 Greek Alpha characters.
String szGreekAlpha = new String('\u0391',5);

// Create a Unicode string with 3 Greek Omega characters.
String szGreekOmega = "\u03A9\u03A9\u03A9";

String szGreekLetters = String.Concat(szGreekOmega, szGreekAlpha, 
                                    szGreekOmega.Clone());

// Display the entire string.
Console.WriteLine("The string: {0}", szGreekLetters);

// The first index of Alpha.
int ialpha = szGreekLetters.IndexOf('\u0391');
// The first index of Omega.
int iomega = szGreekLetters.IndexOf('\u03A9');

Console.WriteLine("First occurrence of the Greek letter Alpha: Index {0}", 
                ialpha);
Console.WriteLine("First occurrence of the Greek letter Omega: Index {0}", 
                iomega);

// The example displays the following output:
//    The string: ΩΩΩΑΑΑΑΑΩΩΩ
//    First occurrence of the Greek letter Alpha: Index 3
//    First occurrence of the Greek letter Omega: Index 0
Public Module Example
   Public Sub Main()
      ' Create a Unicode string with 5 Greek Alpha characters.
      Dim szGreekAlpha As New String(ChrW(&H0391), 5)

      ' Create a Unicode string with 3 Greek Omega characters.
      Dim szGreekOmega As String = ChrW(&H03A9) + ChrW(&H03A9)+
                                   ChrW(&H03A9)

      Dim szGreekLetters As String = String.Concat(szGreekOmega, szGreekAlpha, _
                                                   szGreekOmega.Clone())

      ' Display the entire string.
      Console.WriteLine(szGreekLetters)

      ' The first index of Alpha.
      Dim iAlpha As Integer = szGreekLetters.IndexOf(ChrW(&H0391))
      ' The first index of Omega.
      Dim iomega As Integer = szGreekLetters.IndexOf(ChrW(&H03A9))

      Console.WriteLine("First occurrence of the Greek letter Alpha: Index {0}", 
                        ialpha)
      Console.WriteLine("First occurrence of the Greek letter Omega: Index {0}", 
                        iomega)
   End Sub
End Module
' The example displays the following output:
'       The string: OOO?????OOO
'       First occurrence of the Greek letter Alpha: Index 3
'       First occurrence of the Greek letter Omega: Index 0

注解

索引编号从0开始。Index numbering starts from zero.

此方法执行序号(不区分区域性)搜索,其中,仅当字符的 Unicode 标量值相同时,才将其视为等效于另一个字符。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. 若要执行区分区域性的搜索,请使用 CompareInfo.IndexOf 方法,其中表示预构成字符的 Unicode 标量值(如连字 "Æ" (U + 00C6))可能被视为与正确序列,如 "AE" (U + 0041,U + 0045),具体取决于区域性。To perform a culture-sensitive search, use the CompareInfo.IndexOf 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.

另请参阅

IndexOf(String, Int32)

报告指定字符串在此实例中的第一个匹配项的从零开始的索引。Reports the zero-based index of the first occurrence of the specified string in this instance. 该搜索从指定字符位置开始。The search starts at a specified character position.

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

参数

value
String

要搜寻的字符串。The string to seek.

startIndex
Int32

搜索起始位置。The search starting position.

返回

如果找到该字符串,则为从当前实例的起始位置开始的从零开始的 value 的索引位置;否则为 -1。The zero-based index position of value from the start of the current instance if that string is found, or -1 if it is not. 如果 valueEmpty,则返回值为 startIndexIf value is Empty, the return value is startIndex.

异常

valuenullvalue is null.

startIndex 小于 0(零)或大于此字符串的长度。startIndex is less than 0 (zero) or greater than the length of this string.

示例

下面的示例在目标字符串中搜索指定字符串的所有匹配项。The following example searches for all occurrences of a specified string within a target string.

using namespace System;
int main()
{
   String^ strSource = "This is the string which we will perform the search on";
   Console::WriteLine( "The search string is: {0}\"{1}\" {0}", Environment::NewLine, strSource );
   String^ strTarget = "";
   int found = 0;
   int totFinds = 0;
   do
   {
      Console::Write( "Please enter a search value to look for in the above string (hit Enter to exit) ==> " );
      strTarget = Console::ReadLine();
      if (  !strTarget->Equals( "" ) )
      {
         for ( int i = 0; i < strSource->Length; i++ )
         {
            found = strSource->IndexOf( strTarget, i );
            if (found >= 0)
            {
               totFinds++;
               i = found;
            }
            else
               break;

         }
      }
      else
            return 0;
      Console::WriteLine( "{0}The search parameter '{1}' was found {2} times. {0}", Environment::NewLine, strTarget, totFinds );
      totFinds = 0;
   }
   while ( true );
}

using System;

public class IndexOfTest {
    public static void Main() {

        string strSource = "This is the string which we will perform the search on";

        Console.WriteLine("The search string is:{0}\"{1}\"{0}", Environment.NewLine, strSource);

        string strTarget = "";
        int found = 0;
        int totFinds = 0;

        do {
            Console.Write("Please enter a search value to look for in the above string (hit Enter to exit) ==> ");

            strTarget = Console.ReadLine();

            if (strTarget != "") {

                for (int i = 0; i < strSource.Length; i++) {

                    found = strSource.IndexOf(strTarget, i);

                    if (found >= 0) {
                        totFinds++;
                        i = found;
                    }
                    else
                        break;
                }
            }
            else
                return;

            Console.WriteLine("{0}The search parameter '{1}' was found {2} times.{0}",
                    Environment.NewLine, strTarget, totFinds);

            totFinds = 0;

        } while ( true );
    }
}
Public Class IndexOfTest
    
    Public Shared Sub Main()
        Dim strSource As String = "This is the string which we will perform the search on"
        
        Console.WriteLine("The search string is:{0}{1}{0}", Environment.NewLine, strSource)
        Dim strTarget As String = ""
        Dim found As Integer = 0
        Dim totFinds As Integer = 0
        
        Do
            Console.Write("Please enter a search value to look for in the above string (hit Enter to exit) ==> ")
            
            strTarget = Console.ReadLine()
            If strTarget <> "" Then
                Dim i As Integer
                
                
                For i = 0 To strSource.Length - 1
                    
                    found = strSource.IndexOf(strTarget, i)
                    If found >= 0 Then
                        
                        totFinds += 1
                        i = found
                    Else
                        Exit For
                    End If
                Next i
            Else
                Return
            
            End If
            Console.WriteLine("{0}The search parameter '{1}' was found {2} times.{0}", Environment.NewLine, strTarget, totFinds)
            
            totFinds = 0
        
        Loop While True
    End Sub
End Class

注解

索引编号从0开始。Index numbering starts from 0. startIndex 参数可以介于 0 到字符串实例的长度。The startIndex parameter can range from 0 to the length of the string instance. 如果 startIndex 等于字符串实例的长度,则该方法将返回-1。If startIndex equals the length of the string instance, the method returns -1.

此方法使用当前区域性执行 word (区分大小写和区分区域性的)搜索。This method performs a word (case-sensitive and culture-sensitive) search using the current culture. 搜索从该实例的 startIndex 字符位置开始,并继续到最后一个字符的位置。The search begins at the startIndex character position of this instance and continues until the last character position.

字符集包括可忽略字符,在执行语言性的或区分区域性的比较时该字符不被考虑。Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. 在区分区域性的搜索中,如果 value 包含一个可忽略字符,则结果与移除了该字符的搜索等效。In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. 如果 value 只包含一个或多个可忽略字符,则 IndexOf(String, Int32) 方法始终返回 startIndex,这是搜索开始处的字符位置。If value consists only of one or more ignorable characters, the IndexOf(String, Int32) method always returns startIndex, which is the character position at which the search begins. 在下面的示例中,IndexOf(String, Int32) 方法用于查找软连字符的位置(U + 00AD),后跟两个字符串中的 "m"。In the following example, the IndexOf(String, Int32) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" in two strings. 只有一个字符串包含必需的子字符串。Only one of the strings contains the required substring. 如果该示例在 .NET Framework 4.NET Framework 4 或更高版本上运行,在这两种情况下,因为软连字符是可忽略字符,该方法将返回字符串中的 "m" 的索引。If the example is run on the .NET Framework 4.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. 注意对于第一个字符串,包含软连字符后跟“m”,该方法无法返回该软连字符的索引,而是返回“m”的索引。Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m".

using System;

public class Example
{
    public static void Main()
    {
        string searchString = "\u00ADm";
        string s1 = "ani\u00ADmal" ;
        string s2 = "animal";

        Console.WriteLine(s1.IndexOf(searchString, 2));
        Console.WriteLine(s2.IndexOf(searchString, 2));

        // The example displays the following output:
        //       4
        //       3
    }
}
Module Example
   Public Sub Main()
      Dim searchString As String = Chrw(&h00AD) + "m"
      Dim s1 As String = "ani" + ChrW(&h00AD) + "mal"
      Dim s2 As String = "animal"

      Console.WriteLine(s1.IndexOf(searchString, 2))
      Console.WriteLine(s2.IndexOf(searchString, 2))
   End Sub
End Module
' The example displays the following output:
'       4
'       3 

调用方说明

使用字符串的最佳做法中所述,建议你避免调用替换默认值的字符串比较方法,并改为调用需要显式指定参数的方法。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. 若要使用当前区域性的比较规则查找特定字符位置之后发生的子字符串的第一个索引,请使用其 comparisonType 参数的值 CurrentCulture 调用 IndexOf(String, Int32, StringComparison) 方法重载。To find the first index of a substring that occurs after a particular character position by using the comparison rules of the current culture, call the IndexOf(String, Int32, StringComparison) method overload with a value of CurrentCulture for its comparisonType parameter.

另请参阅

适用于