String.Substring 方法

定义

命名空间:: System

程序集:: mscorlib.dll, System.Runtime.dll

程序集:: mscorlib.dll

程序集:: System.Runtime.dll

程序集:: netstandard.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

从此实例检索子字符串。

此成员重载。有关此成员的完整信息，包括语法、用法和示例，请单击重载列表中的名称。

重载

名称	说明
Substring(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，并继续到字符串的末尾。
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，并具有指定的长度。

Substring(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，并继续到字符串的末尾。

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

与在此实例中开始 startIndex 的子字符串等效的字符串，或者 Empty 如果 startIndex 等于此实例的长度。

例外

ArgumentOutOfRangeException

startIndex 小于零或大于此实例的长度。

示例

以下示例演示如何从字符串获取子字符串。

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 该方法分隔由相等字符=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'

该方法 IndexOf 用于获取字符串中相等字符的位置。对方法的调用 Substring(Int32, Int32) 提取键名称，该名称从字符串中的第一个字符开始，并扩展了调用 IndexOf 方法返回的字符数。然后，对 Substring(Int32) 方法的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，并扩展到字符串的末尾。

注解

调用 Substring(Int32) 该方法从字符串中提取子字符串，该字符串从指定字符位置开始，并在字符串末尾结束。起始字符位置从零开始;换句话说，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结束的子字符串，请调用 Substring(Int32, Int32) 该方法。

注释

此方法不会修改当前实例的值。而是返回从当前字符串中的位置开始 startIndex 的新字符串。

若要提取以特定字符或字符序列开头的子字符串，请调用方法，例如 IndexOf 或 IndexOf 获取其值 startIndex。第二个示例说明了这一点：它提取一个键值，该值在字符之后 = 开始一个字符的位置。

如果 startIndex 等于零，该方法将返回原始字符串不变。

另请参阅

适用于

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，并具有指定的长度。

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

与在此实例中开始的长度length的子字符串等效的字符串，或者Empty如果startIndex等于此实例的长度，则length为startIndex零。

例外

ArgumentOutOfRangeException

startIndex 加号 length 表示此实例中没有的位置。

-或-

startIndex 或 length 小于零。

示例

以下示例演示了从第六个字符位置（即索引 5 处）开始从字符串中提取两个字符的方法的简单调用 Substring(Int32, Int32) 。

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

以下示例使用以下 Substring(Int32, Int32) 三种情况下的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，第三种情况下会引发异常，因为指定了无效参数。

它将提取字符串（索引 2）中第三位置的单个字符，并将其与“c”进行比较。此比较返回 true。
它提取从字符串（索引 3 处）第四个位置开始的零个字符，并将其 IsNullOrEmpty 传递给该方法。这返回 true，因为对方法的 Substring 调用返回 String.Empty。
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，因此该方法调用将引发异常 ArgumentOutOfRangeException 。

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 该方法分隔由相等字符=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) 该方法从字符串中提取子字符串，该字符串从指定字符位置开始，并在字符串末尾之前结束。起始字符位置从零开始;换句话说，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的子字符串，并继续到字符串的末尾，请调用该方法 Substring(Int32) 。

注释

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 从当前字符串中的位置开始 startIndex 的字符。

该 length 参数表示要从当前字符串实例中提取的字符总数。这包括索引处 startIndex找到的起始字符。换句话说，该方法Substring尝试从索引提取字符到索引 + startIndexstartIndexlength - 1。

若要提取以特定字符或字符序列开头的子字符串，请调用方法，例如 IndexOf 或 LastIndexOf 获取其值 startIndex。

如果子字符串应从 startIndex 指定的字符序列扩展，则可以调用方法，例如 IndexOf 或 LastIndexOf 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返回或LastIndexOf方法的IndexOf返回值。以下示例从字符串中提取连续的“b”字符块。

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

如果搜索了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返回或LastIndexOf方法的返回值IndexOf，并且endMatchLength是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返回或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，该方法将返回原始字符串不变。

另请参阅

适用于

反馈

此页面是否有帮助？