String.Substring 方法

定義

命名空間:: System

組件:: mscorlib.dll, System.Runtime.dll

組件:: netstandard.dll, System.Runtime.dll

組件:: System.Runtime.dll

組件:: mscorlib.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

從此實例中擷取一個子字串。

這位成員已經超載了。欲了解此成員的完整資訊，包括語法、用法及範例，請點擊過載清單中的名稱。

多載

名稱	Description
Substring(Int32)	從此實例中擷取一個子字串。子字串從指定的字元位置開始，並一直延伸到字串的末尾。
Substring(Int32, Int32)	從此實例中擷取一個子字串。子字串從指定的字元位置開始，並具有指定的長度。

Substring(Int32)

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

從此實例中擷取一個子字串。子字串從指定的字元位置開始，並一直延伸到字串的末尾。

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

public string Substring(int startIndex);

member this.Substring : int -> string

Public Function Substring (startIndex As Integer) As String

參數

startIndex: Int32

在此實例中子字串的從零開始字元位置。

傳回

String

一個字串等價於本實例中以為的 startIndex 子串，或 Empty 若 startIndex 等於本實例的長度。

例外狀況

ArgumentOutOfRangeException

startIndex 小於零或大於此實例的長度。

範例

以下範例示範如何從字串取得子字串。

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

以下範例使用此 Substring 方法來分離由相等=（）字元分隔的鍵值對。

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'

此 IndexOf 方法用於取得字串中等值字元的位置。呼叫方法 Substring(Int32, Int32) 會擷取金鑰名稱，該名稱從字串的第一個字元開始，並延伸至呼叫回傳 IndexOf 的字元數。呼叫該 Substring(Int32) 方法後，會擷取分配給鍵的值。它從相等字元後方的一個字元位置開始，延伸到字串的末端。

備註

你呼叫 Substring(Int32) 方法，從一個從指定字元位置開始、到字串末尾的字串中提取子字串。起始角色位置為零基礎;換句話說，字串的第一個字元位於索引 0，而非索引 1。若要擷取從指定字元位置開始且在字串末尾前結束的子字串，呼叫該 Substring(Int32, Int32) 方法。

Note

此方法不會修改當前實例的值。取而代之的是，它會回傳一個從當前字串位置開始 startIndex 的新字串。

要擷取以特定字元或字元序列開頭的子串，呼叫如 IndexOf 或 IndexOf 的方法以取得的 startIndex值。第二個例子說明了這一點;它會擷取一個鍵值，該值從字元位置開始 = 。

若 startIndex 等於零，則該方法回傳原始字串不變。

另請參閱

適用於

Substring(Int32, Int32)

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

來源:: String.Manipulation.cs

從此實例中擷取一個子字串。子字串從指定的字元位置開始，並具有指定的長度。

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

參數

startIndex: Int32

在此實例中子字串的從零開始字元位置。

length: Int32

子字串中的字元數。

傳回

String

一個字串等價於本實例中長度為的lengthstartIndex子串，且起點為零，或Empty若 startIndex 等於本實例的長度且length為零。

例外狀況

ArgumentOutOfRangeException

startIndex plus length 表示不屬於此例的局面。

-或-

startIndex 或 length 小於零。

範例

以下範例說明一個簡單的呼叫， Substring(Int32, Int32) 該方法從從第六個字元位置（即索引五）開始的字串中提取兩個字元。

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

以下範例在以下三種情況下使用此 Substring(Int32, Int32) 方法來分離字串中的子字串。在兩種情況下，子字串用於比較，第三種情況則因參數無效而拋出例外。

它會擷取字串第三位（索引 2）的單一字元，並與「c」進行比較。此比較結果 true為。
它從字串第四位置（索引 3）開始擷取零字元，並傳給該 IsNullOrEmpty 方法。此回傳為真，因為呼叫 Substring 方法會回傳 String.Empty。
它嘗試從字串的第四個位置開始提取一個字元。由於該位置沒有字元，方法呼叫會 ArgumentOutOfRangeException 拋出例外。

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

以下範例使用此 Substring 方法來分離由相等=（）字元分隔的鍵值對。

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'

備註

你呼叫 Substring(Int32, Int32) 方法從一個字串開始、在字串結尾之前結束的字串中提取子字串。起始角色位置為零基礎;換句話說，字串的第一個字元位於索引 0，而非索引 1。若要擷取從指定字元位置開始並持續到字串末尾的子串，呼叫該 Substring(Int32) 方法。

Note

此方法不會修改當前實例的值。取而代之的是，它會回傳一個新的字串，字 length 元從 startIndex 當前字串的位置開始。

參數 length 代表從目前字串實例中要提取的總字元數。這包括在索引 startIndex中找到的起始字元。換句話說，該 Substring 方法嘗試從索引 startIndex 到索引 startIndex + length - 1 中提取字元。

要擷取以特定字元或字元序列開頭的子串，呼叫如 IndexOf 或 LastIndexOf 的方法以取得的 startIndex值。

如果子字串應該從 startIndex 延伸到指定的字元序列，你可以呼叫像 IndexOf or LastIndexOf 這類方法來取得結尾字元或字元序列的索引。接著你可以將該值轉換為字串中的索引位置，方法如下：

如果你搜尋一個字元標記子串的結尾，參數length等endIndex - startIndex於 + 1，其中 endIndex 是 or IndexOf 方法的LastIndexOf回傳值。以下範例從字串中擷取連續的「b」字元區塊。

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

如果你搜尋了多個要標記子字串結尾的字元，length參數等endIndex + endMatchLength - startIndex於，其中 endIndex 是 or IndexOf 方法的LastIndexOf回傳值，是endMatchLength標記子串結束的字元序列長度。以下範例擷取包含 XML <definition> 元素的文字區塊。

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>

若字元或字元序列未包含在子字串結尾，length參數等於 endIndex - startIndex，其中 endIndex 是或IndexOf方法的LastIndexOf回傳值。

若 startIndex 等於零且 length 等於當前字串長度，則該方法會回傳原始字串不變。

另請參閱

適用於

意見反應

此頁面對您有幫助嗎？