String.Substring 方法

参考

定义

命名空间:: System

程序集:: System.Runtime.dll

程序集:: mscorlib.dll

程序集:: netstandard.dll

重要

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从此实例检索子字符串。

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Substring(Int32)	从此实例检索子字符串。子字符串在指定的字符位置开始并一直到该字符串的末尾。
Substring(Int32, Int32)	从此实例检索子字符串。子字符串从指定的字符位置开始且具有指定的长度。

Substring(Int32)

Source:: String.Manipulation.cs

Source:: String.Manipulation.cs

Source:: String.Manipulation.cs

从此实例检索子字符串。子字符串在指定的字符位置开始并一直到该字符串的末尾。

public:
 System::String ^ Substring(int startIndex);

public string Substring (int startIndex);

member this.Substring : int -> string

Public Function Substring (startIndex As Integer) As String

参数

startIndex: Int32

此实例中子字符串的起始字符位置（从零开始）。

String

与此实例中在 startIndex 处开头的子字符串等效的一个字符串；如果 Empty 等于此实例的长度，则为 startIndex。

例外

ArgumentOutOfRangeException

startIndex 小于零或大于此实例的长度。

示例

下面的示例演示如何从字符串获取子字符串。

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

let info = 
    [| "Name: Felica Walker"; "Title: Mz."
       "Age: 47"; "Location: Paris"; "Gender: F" |]

printfn "The initial values in the array are:"
for s in info do
    printfn $"{s}"

printfn "\nWe want to retrieve only the key information. That is:"
for s in info do
    let found = s.IndexOf ": "
    printfn $"   {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

以下示例使用 Substring 方法分隔由等于 (=) 字符分隔的键/值对。

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'

let pairs = 
    [| "Color1=red"; "Color2=green"; "Color3=blue"
       "Title=Code Repository" |]
for pair in pairs do
    let position = pair.IndexOf "="
    if position >= 0 then
        printfn $"Key: {pair.Substring(0, position)}, Value: '{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'

方法 IndexOf 用于获取字符串中等于字符的位置。对方法的 Substring(Int32, Int32) 调用提取键名称，该名称从字符串中的第一个字符开始，并扩展对方法的调用 IndexOf 返回的字符数。然后，对方法的 Substring(Int32) 调用将提取分配给键的值。它从等于字符之外的一个字符位置开始，并延伸到字符串的末尾。

注解

调用 Substring(Int32) 方法以从字符串中提取子字符串，该字符串从指定字符位置开始，在字符串末尾结束。起始字符位置从零开始;换言之，字符串中的第一个字符位于索引 0，而不是索引 1。若要提取从指定字符位置开始并在字符串末尾之前结束的子字符串，请 Substring(Int32, Int32) 调用方法。

注意

此方法不会修改当前实例的值。而是返回一个新字符串，该字符串从 startIndex 当前字符串中的位置开始。

若要提取以特定字符或字符序列开头的子字符串，请调用或等IndexOf IndexOf方法来获取的值startIndex。第二个示例说明了这一点：它提取一个键值，该值从字符之后 = 的一个字符位置开始。

如果 startIndex 等于零，则该方法返回原始字符串不变。

另请参阅

适用于

Substring(Int32, Int32)

Source:: String.Manipulation.cs

Source:: String.Manipulation.cs

Source:: String.Manipulation.cs

从此实例检索子字符串。子字符串从指定的字符位置开始且具有指定的长度。

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

参数

startIndex: Int32

此实例中子字符串的起始字符位置（从零开始）。

length: Int32

子字符串中的字符数。

String

与此实例中在 length 处开头、长度为 startIndex 的子字符串等效的一个字符串；如果 Empty 等于此实例的长度且 startIndex 为零，则为 length。

例外

ArgumentOutOfRangeException

startIndex 加 length 指示不在此实例内的位置。

或

startIndex 或 length 小于零。

示例

以下示例演示了对 Substring(Int32, Int32) 方法的简单调用，该方法从字符串中提取两个字符，从第六个字符位置开始， (即索引五) 。

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

let value = "This is a string."
let startIndex = 5
let length = 2
let substring = value.Substring(startIndex, length)
printfn $"{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

以下示例在以下三种情况下使用 Substring(Int32, Int32) 方法隔离字符串中的子字符串。在两种情况下，子字符串用于比较，在第三种情况下，由于指定的参数无效，会引发异常。

它提取字符串中位于索引 2 (第三个位置) 的单个字符，并将其与“c”进行比较。此比较返回 true。
它提取从字符串的第四个位置开始的零个字符 (索引 3) 并将其传递给 IsNullOrEmpty 方法。这会返回 true，因为对方法的Substring String.Empty调用返回。
它尝试从字符串中的第四个位置开始提取一个字符。由于该位置没有字符，因此方法调用会 ArgumentOutOfRangeException 引发异常。

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

let myString = "abc"
let test1 = myString.Substring(2, 1).Equals "c" // This is true.
printfn $"{test1}"
let test2 = String.IsNullOrEmpty(myString.Substring(3, 0)) // This is true.
printfn $"{test2}"
try
    let str3 = myString.Substring(3, 1) // This throws ArgumentOutOfRangeException.
    printfn $"{str3}"
with :? ArgumentOutOfRangeException as e ->
    printfn $"{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

以下示例使用 Substring 方法分隔由等于 (=) 字符分隔的键/值对。

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'

let pairs = 
    [| "Color1=red"; "Color2=green"; "Color3=blue"
       "Title=Code Repository" |]
for pair in pairs do
    let position = pair.IndexOf "="
    if position >= 0 then
        printfn $"Key: {pair.Substring(0, position)}, Value: '{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'

注解

调用 Substring(Int32, Int32) 方法以从字符串中提取子字符串，该字符串从指定的字符位置开始，在字符串末尾之前结束。起始字符位置从零开始;换言之，字符串中的第一个字符位于索引 0，而不是索引 1。若要提取从指定字符位置开始并一直延续到字符串末尾的子字符串，请 Substring(Int32) 调用方法。

注意

此方法不会修改当前实例的值。而是返回一个新字符串，其中包含 length 从 startIndex 当前字符串中的位置开始的字符。

参数 length 表示要从当前字符串实例中提取的字符总数。这包括在索引 startIndex中找到的起始字符。换句话说， Substring 方法尝试将字符从索引 startIndex 提取到索引 startIndex + length - 1。

若要提取以特定字符或字符序列开头的子字符串，请调用或等IndexOf LastIndexOf方法来获取的值startIndex。

如果子字符串应从 startIndex 扩展到指定的字符序列，则可以调用或等IndexOf LastIndexOf方法来获取结束字符或字符序列的索引。然后，可以将该值转换为字符串中的索引位置，如下所示：

如果已搜索要标记子字符串末尾的单个字符，则 length 参数等于 - startIndexendIndex+ 1，其中 endIndex 是或 LastIndexOf 方法的IndexOf返回值。以下示例从字符串中提取“b”字符的连续块。

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

let s = "aaaaabbbcccccccdd"
let charRange = 'b'
let startIndex = s.IndexOf charRange
let endIndex = s.LastIndexOf charRange
let length = endIndex - startIndex + 1
printfn $"{s}.Substring({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

如果已搜索要标记子字符串末尾的多个字符，则 length 参数等于 - endMatchLength + endIndexstartIndex ，其中 endIndex 是或 LastIndexOf 方法的IndexOf返回值，是endMatchLength标记子字符串末尾的字符序列的长度。以下示例提取包含 XML <definition> 元素的文本块。

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>

let s = "<term>extant<definition>still in existence</definition></term>"
let searchString = "<definition>"
let startIndex = s.IndexOf(searchString)
let searchString = "</" + searchString.Substring 1
let endIndex = s.IndexOf searchString
let substring = s.Substring(startIndex, endIndex + searchString.Length - startIndex)
printfn $"Original string: {s}"
printfn $"Substring;       {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>

如果子字符串末尾不包含字符或字符序列，则 length 参数等于 endIndexstartIndex - ，其中 endIndex 是或 LastIndexOf 方法的IndexOf返回值。

如果 startIndex 等于零且 length 等于当前字符串的长度，则该方法返回原始字符串不变。

另请参阅

适用于

String.Substring 方法

定义

重载

Substring(Int32)

参数

返回

例外

示例

注解

另请参阅

适用于

Substring(Int32, Int32)

参数

返回

例外

示例

注解

另请参阅

适用于

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