String.Substring 方法

定義

從這個執行個體擷取子字串。Retrieves a substring from this instance.

這個成員是多載的。This member is overloaded. 如需這個成員的完整資訊,包含語法、使用方式和範例,請按一下多載清單中的名稱。For complete information about this member, including syntax, usage, and examples, click a name in the overload list.

多載

Substring(Int32)

從這個執行個體擷取子字串。Retrieves a substring from this instance. 子字串會在指定的字元位置開始並繼續到字串的結尾。The substring starts at a specified character position and continues to the end of the string.

Substring(Int32, Int32)

從這個執行個體擷取子字串。Retrieves a substring from this instance. 子字串起始於指定的字元位置,並且具有指定的長度。The substring starts at a specified character position and has a specified length.

Substring(Int32)

從這個執行個體擷取子字串。Retrieves a substring from this instance. 子字串會在指定的字元位置開始並繼續到字串的結尾。The substring starts at a specified character position and continues to the end of the string.

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

參數

startIndex
Int32

這個執行個體中子字串之以零為起始的起始字元位置。The zero-based starting character position of a substring in this instance.

傳回

String

與這個執行個體中從 startIndex 開始之子字串相等的字串;如果 Empty 等於這個執行個體的長度,則為 startIndexA string that is equivalent to the substring that begins at startIndex in this instance, or Empty if startIndex is equal to the length of this instance.

例外狀況

startIndex 小於零或大於此執行個體的長度。startIndex is less than zero or greater than the length of this instance.

範例

下列範例示範如何從字串取得子字串。The following example demonstrates obtaining a substring from a string.

using namespace System;
using namespace System::Collections;

int main()
{
   array<String^>^info = { "Name: Felica Walker", "Title: Mz.",
                           "Age: 47", "Location: Paris", "Gender: F"};
   int found = 0;
   Console::WriteLine("The initial values in the array are:");
   for each (String^ s in info) 
      Console::WriteLine(s);

   Console::WriteLine("\nWe want to retrieve only the key information. That is:");
   for each (String^ s in info) { 
      found = s->IndexOf(": ");
      Console::WriteLine("   {0}", s->Substring(found + 2));
   }
}
// The example displays the following output:
//       The initial values in the array are:
//       Name: Felica Walker
//       Title: Mz.
//       Age: 47
//       Location: Paris
//       Gender: F
//       
//       We want to retrieve only the key information. That is:
//       Felica Walker
//       Mz.
//       47
//       Paris
//       F
string [] info = { "Name: Felica Walker", "Title: Mz.", 
                   "Age: 47", "Location: Paris", "Gender: F"};
int found = 0;

Console.WriteLine("The initial values in the array are:");
foreach (string s in info)
    Console.WriteLine(s);

Console.WriteLine("\nWe want to retrieve only the key information. That is:");        
foreach (string s in info) 
{
    found = s.IndexOf(": ");
    Console.WriteLine("   {0}", s.Substring(found + 2));
}

// The example displays the following output:
//       The initial values in the array are:
//       Name: Felica Walker
//       Title: Mz.
//       Age: 47
//       Location: Paris
//       Gender: F
//       
//       We want to retrieve only the key information. That is:
//          Felica Walker
//          Mz.
//          47
//          Paris
//          F
Public Class SubStringTest
    Public Shared Sub Main()
        Dim info As String() = { "Name: Felica Walker", "Title: Mz.", 
                                 "Age: 47", "Location: Paris", "Gender: F"}
        Dim found As Integer = 0
       
        Console.WriteLine("The initial values in the array are:")
        For Each s As String In info
            Console.WriteLine(s)
        Next s

        Console.WriteLine(vbCrLf + "We want to retrieve only the key information. That is:")
        For Each s As String In info
            found = s.IndexOf(": ")
            Console.WriteLine("   {0}", s.Substring(found + 2))
        Next s
    End Sub 
End Class 
' The example displays the following output:
'       The initial values in the array are:
'       Name: Felica Walker
'       Title: Mz.
'       Age: 47
'       Location: Paris
'       Gender: F
'       
'       We want to retrieve only the key information. That is:
'          Felica Walker
'          Mz.
'          47
'          Paris
'          F

下列範例 Substring 會使用方法來分隔索引鍵/值組(以等於 ( "=" ) 字元分隔)。The following example uses the Substring method to separate key/value pairs that are delimited by an equals ("=") character.

String[] pairs = { "Color1=red", "Color2=green", "Color3=blue",
                 "Title=Code Repository" };
foreach (var pair in pairs) 
{
    int position = pair.IndexOf("=");
    if (position < 0)
        continue;
    Console.WriteLine("Key: {0}, Value: '{1}'", 
                   pair.Substring(0, position),
                   pair.Substring(position + 1));
}                          

// The example displays the following output:
//     Key: Color1, Value: 'red'
//     Key: Color2, Value: 'green'
//     Key: Color3, Value: 'blue'
//     Key: Title, Value: 'Code Repository'
Module Example
   Public Sub Main()
      Dim pairs() As String = { "Color1=red", "Color2=green", "Color3=blue",
                                "Title=Code Repository" }
      For Each pair In pairs
         Dim position As Integer = pair.IndexOf("=")
         If position < 0 then Continue For
         Console.WriteLine("Key: {0}, Value: '{1}'", 
                           pair.Substring(0, position),
                           pair.Substring(position + 1))
      Next                          
   End Sub
End Module
' The example displays the following output:
'     Key: Color1, Value: 'red'
'     Key: Color2, Value: 'green'
'     Key: Color3, Value: 'blue'
'     Key: Title, Value: 'Code Repository'

IndexOf方法是用來取得字串中等號字元的位置。The IndexOf method is used to get the position of the equals character in the string. 方法的呼叫會 Substring(Int32, Int32) 從字串中的第一個字元開始,以及針對方法呼叫所傳回的字元數進行擴充,以解壓縮索引鍵名稱 IndexOfThe call to the Substring(Int32, Int32) method extracts the key name, which starts from the first character in the string and extends for the number of characters returned by the call to the IndexOf method. 然後,對方法的呼叫會將指派給索引 Substring(Int32) 鍵的值解壓縮。The call to the Substring(Int32) method then extracts the value assigned to the key. 它會從等於字元的一個字元位置開始,並延伸至字串結尾。It starts at one character position beyond the equals character and extends to the end of the string.

備註

您可以呼叫 Substring(Int32) 方法,從起始于指定字元位置的字串解壓縮子字串,並在字串的結尾結束。You call the Substring(Int32) method to extract a substring from a string that begins at a specified character position and ends at the end of the string. 起始字元位置是以零為基底;換句話說,字串中的第一個字元位於索引0,而非索引1。The starting character position is a zero-based; in other words, the first character in the string is at index 0, not index 1. 若要從指定的字元位置開始,並在字串結尾的結尾處解壓縮子字串,請呼叫 Substring(Int32, Int32) 方法。To extract a substring that begins at a specified character position and ends before the end of the string, call the Substring(Int32, Int32) method.

注意

這個方法不會修改目前實例的值。This method does not modify the value of the current instance. 相反地,它會傳回新的字串,此字串會從 startIndex 目前字串的位置開始。Instead, it returns a new string that begins at the startIndex position in the current string.

若要解壓縮以特定字元或字元序列開頭的子字串,請呼叫的方法(例如 IndexOf 或) IndexOf 來取得的值 startIndexTo extract a substring that begins with a particular character or character sequence, call a method such as IndexOf or IndexOf to get the value of startIndex. 第二個範例說明這一點;它會解壓縮在 "=" 字元之後開始一個字元位置的索引鍵值。The second example illustrates this; it extracts a key value that begins one character position after the "=" character.

如果 startIndex 等於零,則方法會傳回未變更的原始字串。If startIndex is equal to zero, the method returns the original string unchanged.

另請參閱

適用於

Substring(Int32, Int32)

從這個執行個體擷取子字串。Retrieves a substring from this instance. 子字串起始於指定的字元位置,並且具有指定的長度。The substring starts at a specified character position and has a specified length.

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

參數

startIndex
Int32

這個執行個體中子字串之以零為起始的起始字元位置。The zero-based starting character position of a substring in this instance.

length
Int32

子字串中的字元數。The number of characters in the substring.

傳回

String

與長度為 length 且在這個執行個體中從 startIndex 開始之子字串相等的字串;如果 Empty 等於這個執行個體的長度且 startIndex 為零,則為 lengthA string that is equivalent to the substring of length length that begins at startIndex in this instance, or Empty if startIndex is equal to the length of this instance and length is zero.

例外狀況

startIndex 加上 length 表示不在此執行個體中的位置。startIndex plus length indicates a position not within this instance.

-或--or-

startIndexlength 小於零。startIndex or length is less than zero.

範例

下列範例說明簡單的 Substring(Int32, Int32) 方法呼叫,該方法會從第六個字元位置開始的字串中解壓縮兩個字元 (也就是在索引 5) 。The following example illustrates a simple call to the Substring(Int32, Int32) method that extracts two characters from a string starting at the sixth character position (that is, at index five).

String value = "This is a string.";
int startIndex = 5;
int length = 2;
String substring = value.Substring(startIndex, length);
Console.WriteLine(substring);

// The example displays the following output:
//       is
Module Example
   Public Sub Main()
      Dim value As String = "This is a string."
      Dim startIndex As Integer = 5
      Dim length As Integer = 2
      Dim substring As String = value.Substring(startIndex, length)
      Console.WriteLine(substring)
   End Sub
End Module
' The example displays the following output:
'       is

下列範例會使用 Substring(Int32, Int32) 下列三種案例中的方法來隔離字串內的子字串。The following example uses the Substring(Int32, Int32) method in the following three cases to isolate substrings within a string. 在兩種情況下,會使用子字串進行比較,在第三個案例中會擲回例外狀況,因為指定的參數無效。In two cases the substrings are used in comparisons, and in the third case an exception is thrown because invalid parameters are specified.

  • 它會將字串中 (的單一字元和第三個位置解壓縮) ,並與 "c" 進行比較。It extracts the single character and the third position in the string (at index 2) and compares it with a "c". 這種比較會傳回 trueThis comparison returns true.

  • 它會在索引 3) 字串 (的第四個位置開始解壓縮零個字元,並將它傳遞給 IsNullOrEmpty 方法。It extracts zero characters starting at the fourth position in the string (at index 3) and passes it to the IsNullOrEmpty method. 這會傳回 true,因為呼叫 Substring 方法會傳回 String.EmptyThis returns true because the call to the Substring method returns String.Empty.

  • 它會嘗試從字串中的第四個位置開始解壓縮一個字元。It attempts to extract one character starting at the fourth position in the string. 因為該位置沒有任何字元,方法呼叫會擲回例外狀況 ArgumentOutOfRangeExceptionBecause there is no character at that position, the method call throws an ArgumentOutOfRangeException exception.

String myString = "abc";
bool test1 = myString.Substring(2, 1).Equals("c"); // This is true.
Console.WriteLine(test1);
bool test2 = String.IsNullOrEmpty(myString.Substring(3, 0)); // This is true.
Console.WriteLine(test2);
try
{
   string str3 = myString.Substring(3, 1); // This throws ArgumentOutOfRangeException.
   Console.WriteLine(str3);
}
catch (ArgumentOutOfRangeException e)
{
   Console.WriteLine(e.Message);
}

// The example displays the following output:
//       True
//       True
//       Index and length must refer to a location within the string.
//       Parameter name: length
Public Class Sample
   Public Shared Sub Main()
      Dim myString As String = "abc"
      Dim test1 As Boolean = myString.Substring(2, 1).Equals("c") ' This is true.
      Console.WriteLine(test1)
      Dim test2 As Boolean = String.IsNullOrEmpty(myString.Substring(3, 0)) ' This is true.
      Console.WriteLine(test2)
      Try  
         Dim str3 As String = myString.Substring(3, 1) ' This throws ArgumentOutOfRangeException.
         Console.WriteLine(str3)
      Catch e As ArgumentOutOfRangeException
         Console.WriteLIne(e.Message)
      End Try   
   End Sub
End Class 
' The example displays the following output:
'       True
'       True
'       Index and length must refer to a location within the string.
'       Parameter name: length

下列範例 Substring 會使用方法來分隔索引鍵/值組(以等於 ( "=" ) 字元分隔)。The following example uses the Substring method to separate key/value pairs that are delimited by an equals ("=") character.

String[] pairs = { "Color1=red", "Color2=green", "Color3=blue",
                 "Title=Code Repository" };
foreach (var pair in pairs) 
{
    int position = pair.IndexOf("=");
    if (position < 0)
        continue;
    Console.WriteLine("Key: {0}, Value: '{1}'", 
                   pair.Substring(0, position),
                   pair.Substring(position + 1));
}                          

// The example displays the following output:
//     Key: Color1, Value: 'red'
//     Key: Color2, Value: 'green'
//     Key: Color3, Value: 'blue'
//     Key: Title, Value: 'Code Repository'
Module Example
   Public Sub Main()
      Dim pairs() As String = { "Color1=red", "Color2=green", "Color3=blue",
                                "Title=Code Repository" }
      For Each pair In pairs
         Dim position As Integer = pair.IndexOf("=")
         If position < 0 then Continue For
         Console.WriteLine("Key: {0}, Value: '{1}'", 
                           pair.Substring(0, position),
                           pair.Substring(position + 1))
      Next                          
   End Sub
End Module
' The example displays the following output:
'     Key: Color1, Value: 'red'
'     Key: Color2, Value: 'green'
'     Key: Color3, Value: 'blue'
'     Key: Title, Value: 'Code Repository'

IndexOf方法是用來取得字串中等號字元的位置。The IndexOf method is used to get the position of the equals character in the string. 方法的呼叫會 Substring(Int32, Int32) 從字串中的第一個字元開始,以及針對方法呼叫所傳回的字元數進行擴充,以解壓縮索引鍵名稱 IndexOfThe call to the Substring(Int32, Int32) method extracts the key name, which starts from the first character in the string and extends for the number of characters returned by the call to the IndexOf method. 然後,對方法的呼叫會將指派給索引 Substring(Int32) 鍵的值解壓縮。The call to the Substring(Int32) method then extracts the value assigned to the key. 它會從等於字元的一個字元位置開始,並延伸至字串結尾。It starts at one character position beyond the equals character and extends to the end of the string.

備註

您可以呼叫 Substring(Int32, Int32) 方法,從起始于指定字元位置的字串解壓縮子字串,並在字串結尾之前結束。You call the Substring(Int32, Int32) method to extract a substring from a string that begins at a specified character position and ends before the end of the string. 起始字元位置是以零為基底;換句話說,字串中的第一個字元位於索引0,而非索引1。The starting character position is a zero-based; in other words, the first character in the string is at index 0, not index 1. 若要從指定的字元位置開始解壓縮開頭的子字串,並繼續到字串的結尾,請呼叫 Substring(Int32) 方法。To extract a substring that begins at a specified character position and continues to the end of the string, call the Substring(Int32) method.

注意

這個方法不會修改目前實例的值。This method does not modify the value of the current instance. 相反地,它會傳回新的字串,其中包含 lengthstartIndex 目前字串中的位置開始的字元。Instead, it returns a new string with length characters starting from the startIndex position in the current string.

length參數代表要從目前的字串實例中解壓縮的字元總數。The length parameter represents the total number of characters to extract from the current string instance. 這包括在索引處找到的起始字元 startIndexThis includes the starting character found at index startIndex. 換句話說, Substring 方法會嘗試將索引中的字元解壓縮 startIndex 至 index startIndex + length -1。In other words, the Substring method attempts to extract characters from index startIndex to index startIndex + length - 1.

若要解壓縮以特定字元或字元序列開頭的子字串,請呼叫的方法(例如 IndexOf 或) LastIndexOf 來取得的值 startIndexTo extract a substring that begins with a particular character or character sequence, call a method such as IndexOf or LastIndexOf to get the value of startIndex.

如果子字串從延伸 startIndex 至指定的字元序列,您可以呼叫方法(例如 IndexOf 或) LastIndexOf 來取得結束字元或字元序列的索引。If the substring extends from startIndex to a specified character sequence, you can call a method such as IndexOf or LastIndexOf to get the index of the ending character or character sequence. 然後,您可以將該值轉換成字串中的索引位置,如下所示:You can then convert that value to an index position in the string as follows:

  • 如果您已搜尋要標示子字串結尾的單一字元, length 參數等於 endIndex - startIndex + 1,其中 endIndex 是或方法的傳回值 IndexOf IndexOfIf you've searched for a single character that is to mark the end of the substring, the length parameter equals endIndex - startIndex + 1, where endIndex is the return value of the IndexOf or IndexOf method. 下列範例會從字串中解壓縮 "b" 個字元的連續區塊。The following example extracts a continuous block of "b" characters from a string.

    String s = "aaaaabbbcccccccdd";
    Char charRange = 'b';
    int startIndex = s.IndexOf(charRange);
    int endIndex = s.LastIndexOf(charRange);
    int length = endIndex - startIndex + 1;
    Console.WriteLine("{0}.Substring({1}, {2}) = {3}",
                    s, startIndex, length, 
                    s.Substring(startIndex, length));
    
    // The example displays the following output:
    //       aaaaabbbcccccccdd.Substring(5, 3) = bbb
    
    Module Example
       Public Sub Main()
          Dim s As String = "aaaaabbbcccccccdd"
          Dim charRange As Char = "b"c
          Dim startIndex As Integer = s.Indexof(charRange)
          Dim endIndex As Integer = s.LastIndexOf(charRange)
          Dim length = endIndex - startIndex + 1
          Console.WriteLine("{0}.Substring({1}, {2}) = {3}",
                            s, startIndex, length, 
                            s.Substring(startIndex, length))
       End Sub
    End Module
    ' The example displays the following output:
    '     aaaaabbbcccccccdd.Substring(5, 3) = bbb
    
  • 如果您已搜尋要標示子字串結尾的多個字元, length 參數等於 endIndex + endMatchLength - startIndex ,其中 endIndex 是或方法的傳回值 IndexOf IndexOf ,而 endMatchLength 則是標示子字串結尾的字元序列長度。If you've searched for multiple characters that are to mark the end of the substring, the length parameter equals endIndex + endMatchLength - startIndex, where endIndex is the return value of the IndexOf or IndexOf method, and endMatchLength is the length of the character sequence that marks the end of the substring. 下列範例會解壓縮包含 XML 元素的文字區塊 <definition>The following example extracts a block of text that contains an XML <definition> element.

    String s = "<term>extant<definition>still in existence</definition></term>";
    String searchString = "<definition>";
    int startIndex = s.IndexOf(searchString);
    searchString = "</" + searchString.Substring(1);
    int endIndex = s.IndexOf(searchString);
    String substring = s.Substring(startIndex, endIndex + searchString.Length - startIndex);
    Console.WriteLine("Original string: {0}", s);
    Console.WriteLine("Substring;       {0}", substring); 
    
    // The example displays the following output:
    //     Original string: <term>extant<definition>still in existence</definition></term>
    //     Substring;       <definition>still in existence</definition>
    
    Module Example
       Public Sub Main()
          Dim s As String = "<term>extant<definition>still in existence</definition></term>"
          Dim searchString As String = "<definition>"
          Dim startindex As Integer = s.IndexOf(searchString)
          searchString = "</" + searchString.Substring(1)
          Dim endIndex As Integer = s.IndexOf(searchString)
          Dim substring As String = s.Substring(startIndex, endIndex + searchString.Length - StartIndex)
          Console.WriteLine("Original string: {0}", s)
          Console.WriteLine("Substring;       {0}", substring) 
       End Sub
    End Module
    ' The example displays the following output:
    '   Original string: <term>extant<definition>still in existence</definition></term>
    '   Substring;       <definition>still in existence</definition>
    
  • 如果字元或字元序列未包含在子字串的結尾, length 參數等於 endIndex - startIndex ,其中 endIndex 是或方法的傳回值 IndexOf IndexOfIf the character or character sequence is not included in the end of the substring, the length parameter equals endIndex - startIndex, where endIndex is the return value of the IndexOf or IndexOf method.

如果 startIndex 等於零且等於目前字串的長度,則方法會傳回未變更的原始字串。If startIndex is equal to zero and equals the length of the current string, the method returns the original string unchanged.

另請參閱

適用於