通过

String.StartsWith 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

重载

StartsWith(String, Boolean, CultureInfo)

确定在使用指定的区域性进行比较时此字符串实例的开头是否与指定的字符串匹配。
StartsWith(String, StringComparison)

确定在使用指定的比较选项进行比较时此字符串实例的开头是否与指定的字符串匹配。
StartsWith(Char)

确定此字符串实例是否以指定字符开始。
StartsWith(String)

确定此字符串实例的开头是否与指定的字符串匹配。

StartsWith(String, Boolean, CultureInfo)

Source:
String.Comparison.cs
Source:
String.Comparison.cs
Source:
String.Comparison.cs

确定在使用指定的区域性进行比较时此字符串实例的开头是否与指定的字符串匹配。

public:
 bool StartsWith(System::String ^ value, bool ignoreCase, System::Globalization::CultureInfo ^ culture);
public bool StartsWith (string value, bool ignoreCase, System.Globalization.CultureInfo? culture);
public bool StartsWith (string value, bool ignoreCase, System.Globalization.CultureInfo culture);
member this.StartsWith : string * bool * System.Globalization.CultureInfo -> bool
Public Function StartsWith (value As String, ignoreCase As Boolean, culture As CultureInfo) As Boolean

参数

value
String

要比较的字符串。

ignoreCase
Boolean

若要在比较过程中忽略大小写，则为 true；否则为 false。

culture
CultureInfo

确定如何对此字符串与 value 进行比较的区域性信息。 如果 culture 为 null，则使用当前区域性。

返回

Boolean

如果 true 参数与此字符串的开头匹配，则为 value；否则为 false。

例外

ArgumentNullException

value 为 null。

示例

以下示例确定字符串是否出现在另一个字符串的开头。 使用 StartsWith 区分大小写、不区分大小写以及影响搜索结果的不同区域性多次调用 方法。

// This code example demonstrates the 
// System.String.StartsWith(String, ..., CultureInfo) method.

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

class Sample 
{
    public static void Main() 
    {
    string msg1 = "Search for the target string \"{0}\" in the string \"{1}\".\n";
    string msg2 = "Using the {0} - \"{1}\" culture:";
    string msg3 = "  The string to search ends with the target string: {0}";
    bool result = false;
    CultureInfo ci;

// Define a target string to search for.
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    string capitalARing = "\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 aRingXYZ = "\u0061\u030a" + "xyz";

// Clear the screen and display an introduction.
    Console.Clear();

// Display the string to search for and the string to search.
    Console.WriteLine(msg1, capitalARing, aRingXYZ);

// Search using English-United States culture.
    ci = new CultureInfo("en-US");
    Console.WriteLine(msg2, ci.DisplayName, ci.Name);

    Console.WriteLine("Case sensitive:");
    result = aRingXYZ.StartsWith(capitalARing, false, ci);
    Console.WriteLine(msg3, result);

    Console.WriteLine("Case insensitive:");
    result = aRingXYZ.StartsWith(capitalARing, true, ci);
    Console.WriteLine(msg3, result);
    Console.WriteLine();

// Search using Swedish-Sweden culture.
    ci = new CultureInfo("sv-SE");
    Console.WriteLine(msg2, ci.DisplayName, ci.Name);

    Console.WriteLine("Case sensitive:");
    result = aRingXYZ.StartsWith(capitalARing, false, ci);
    Console.WriteLine(msg3, result);

    Console.WriteLine("Case insensitive:");
    result = aRingXYZ.StartsWith(capitalARing, true, ci);
    Console.WriteLine(msg3, result);
    }
}

/*
Note: This code example was executed on a console whose user interface 
culture is "en-US" (English-United States).

Search for the target string "Å" in the string "a°xyz".

Using the English (United States) - "en-US" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: True

Using the Swedish (Sweden) - "sv-SE" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: False

*/

// This code example demonstrates the
// System.String.StartsWith(String, ..., CultureInfo) method.

open System
open System.Globalization
 
[<EntryPoint>]
let main _ =
    let msg1 = "Search for the target string \"{0}\" in the string \"{1}\".\n"
    let msg2 = "Using the {0} - \"{1}\" culture:"
    let msg3 = "  The string to search ends with the target string: {0}"

    // Define a target string to search for.
    // U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    let capitalARing = "\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).
    let aRingXYZ = "\u0061\u030a" + "xyz"

    // Clear the screen and display an introduction.
    Console.Clear()

    // Display the string to search for and the string to search.
    Console.WriteLine(msg1, capitalARing, aRingXYZ)

    // Search using English-United States culture.
    let ci = CultureInfo "en-US"
    Console.WriteLine(msg2, ci.DisplayName, ci.Name)

    printfn "Case sensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, false, ci)
    Console.WriteLine(msg3, result)

    printfn "Case insensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, true, ci)
    Console.WriteLine(msg3, result)
    printfn ""

    // Search using Swedish-Sweden culture.
    let ci = CultureInfo "sv-SE"
    Console.WriteLine(msg2, ci.DisplayName, ci.Name)

    printfn "Case sensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, false, ci)
    Console.WriteLine(msg3, result)

    printfn "Case insensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, true, ci)
    Console.WriteLine(msg3, result)
    0
(*
Note: This code example was executed on a console whose user interface
culture is "en-US" (English-United States).

Search for the target string "Å" in the string "a°xyz".

Using the English (United States) - "en-US" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: True

Using the Swedish (Sweden) - "sv-SE" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: False

*)

' This code example demonstrates the 
' System.String.StartsWith(String, ..., CultureInfo) method.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim msg1 As String = "Search for the target string ""{0}"" in the string ""{1}""." & vbCrLf
        Dim msg2 As String = "Using the {0} - ""{1}"" culture:"
        Dim msg3 As String = "  The string to search ends with the target string: {0}"
        Dim result As Boolean = False
        Dim ci As CultureInfo
        
        ' Define a target string to search for.
        ' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
        Dim capitalARing 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 aRingXYZ As String = "å" & "xyz"
        
        ' Clear the screen and display an introduction.
        Console.Clear()
        
        ' Display the string to search for and the string to search.
        Console.WriteLine(msg1, capitalARing, aRingXYZ)
        
        ' Search using English-United States culture.
        ci = New CultureInfo("en-US")
        Console.WriteLine(msg2, ci.DisplayName, ci.Name)
        
        Console.WriteLine("Case sensitive:")
        result = aRingXYZ.StartsWith(capitalARing, False, ci)
        Console.WriteLine(msg3, result)
        
        Console.WriteLine("Case insensitive:")
        result = aRingXYZ.StartsWith(capitalARing, True, ci)
        Console.WriteLine(msg3, result)
        Console.WriteLine()
        
        ' Search using Swedish-Sweden culture.
        ci = New CultureInfo("sv-SE")
        Console.WriteLine(msg2, ci.DisplayName, ci.Name)
        
        Console.WriteLine("Case sensitive:")
        result = aRingXYZ.StartsWith(capitalARing, False, ci)
        Console.WriteLine(msg3, result)
        
        Console.WriteLine("Case insensitive:")
        result = aRingXYZ.StartsWith(capitalARing, True, ci)
        Console.WriteLine(msg3, result)
    
    End Sub
End Class

'
'Note: This code example was executed on a console whose user interface 
'culture is "en-US" (English-United States).
'
'Search for the target string "Å" in the string "a°xyz".
'
'Using the English (United States) - "en-US" culture:
'Case sensitive:
'  The string to search ends with the target string: False
'Case insensitive:
'  The string to search ends with the target string: True
'
'Using the Swedish (Sweden) - "sv-SE" culture:
'Case sensitive:
'  The string to search ends with the target string: False
'Case insensitive:
'  The string to search ends with the target string: False
'

注解

此方法将 value 参数与此字符串开头的子字符串进行比较，该字符串的长度与 value相同，并返回一个值，该值指示它们是否相等。 若要相等， value 必须是空字符串 (String.Empty) ，必须是对此同一实例的引用，或者必须与此实例的开头匹配。

此方法使用指定的大小写和区域性执行比较。

适用于

StartsWith(String, StringComparison)

Source:
String.Comparison.cs
Source:
String.Comparison.cs
Source:
String.Comparison.cs

确定在使用指定的比较选项进行比较时此字符串实例的开头是否与指定的字符串匹配。

public:
 bool StartsWith(System::String ^ value, StringComparison comparisonType);
public bool StartsWith (string value, StringComparison comparisonType);
[System.Runtime.InteropServices.ComVisible(false)]
public bool StartsWith (string value, StringComparison comparisonType);
member this.StartsWith : string * StringComparison -> bool
[<System.Runtime.InteropServices.ComVisible(false)>]
member this.StartsWith : string * StringComparison -> bool
Public Function StartsWith (value As String, comparisonType As StringComparison) As Boolean

参数

value
String

要比较的字符串。

comparisonType
StringComparison

枚举值之一，用于确定如何比较此字符串与 value。

返回

Boolean

如果此实例以 true 开头，则为 value；否则为 false。

属性
ComVisibleAttribute

例外

ArgumentNullException

value 为 null。

ArgumentException

comparisonType 不是 StringComparison 值。

示例

以下示例在以单词“The”开头的较长字符串的开头搜索字符串“the”。 如示例输出所示，对 StartsWith(String, StringComparison) 执行不区分区域性但区分大小写比较的方法的调用无法匹配字符串，而执行区域性和不区分大小写比较的调用与字符串匹配。

using namespace System;

void main()
{
   String^ title = "The House of the Seven Gables";
   String^ searchString = "the";
   StringComparison comparison = StringComparison::InvariantCulture;
   Console::WriteLine("'{0}':", title);
   Console::WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                      searchString, comparison,
                      title->StartsWith(searchString, comparison));

   comparison = StringComparison::InvariantCultureIgnoreCase;
   Console::WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                      searchString, comparison,
                      title->StartsWith(searchString, comparison));
   }
// The example displays the following output:
//       'The House of the Seven Gables':
//          Starts with 'the' (InvariantCulture comparison): False
//          Starts with 'the' (InvariantCultureIgnoreCase comparison): True

using System;

public class Example
{
   public static void Main()
   {
      String title = "The House of the Seven Gables";
      String searchString = "the";
      StringComparison comparison = StringComparison.InvariantCulture;
      Console.WriteLine("'{0}':", title);
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison));

      comparison = StringComparison.InvariantCultureIgnoreCase;
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison));
   }
}
// The example displays the following output:
//       'The House of the Seven Gables':
//          Starts with 'the' (InvariantCulture comparison): False
//          Starts with 'the' (InvariantCultureIgnoreCase comparison): True

open System

let title = "The House of the Seven Gables"
let searchString = "the"
let comparison = StringComparison.InvariantCulture
printfn $"'{title}':"
printfn $"   Starts with '{searchString}' ({comparison:G} comparison): {title.StartsWith(searchString, comparison)}"

let comparison2 = StringComparison.InvariantCultureIgnoreCase
printfn $"   Starts with '{searchString}' ({comparison2:G} comparison): {title.StartsWith(searchString, comparison2)}"
// The example displays the following output:
//       'The House of the Seven Gables':
//          Starts with 'the' (InvariantCulture comparison): False
//          Starts with 'the' (InvariantCultureIgnoreCase comparison): True

Module Example
   Public Sub Main()
      Dim title As String = "The House of the Seven Gables"
      Dim searchString As String = "the"
      Dim comparison As StringComparison = StringComparison.InvariantCulture
      Console.WriteLine("'{0}':", title)
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison))

      comparison = StringComparison.InvariantCultureIgnoreCase
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison))
   End Sub
End Module
' The example displays the following output:
'    'The House of the Seven Gables':
'       Starts with 'the' (InvariantCulture comparison): False
'       Starts with 'the' (InvariantCultureIgnoreCase comparison): True

以下示例确定字符串是否以特定子字符串开头。 它初始化二维字符串数组。 第二个维度中的第一个元素包含一个字符串，第二个元素包含在第一个字符串的开头要搜索的字符串。 结果受区域性选择、是否忽略大小写以及是否执行序号比较的影响。 请注意，当字符串实例包含连字时，区分区域性的比较与其连续字符会成功匹配。

using namespace System;

void main()
{
   array<String^, 2>^ strings = gcnew array<String^, 2> { {"ABCdef", "abc" },                    
                         {"ABCdef", "abc" }, {"œil","oe" }, 
                         { "læring}", "lae" } };
   for (int ctr1 = strings->GetLowerBound(0); ctr1 <= strings->GetUpperBound(0); ctr1++)
   {
         for each (String^ cmpName in Enum::GetNames(StringComparison::typeid))
         { 
            StringComparison strCmp = (StringComparison) Enum::Parse(StringComparison::typeid, 
                                                         cmpName);
            String^ instance = strings[ctr1, 0];
            String^ value = strings[ctr1, 1];
            Console::WriteLine("{0} starts with {1}: {2} ({3} comparison)", 
                               instance, value, 
                               instance->StartsWith(value, strCmp), 
                               strCmp); 
         }
         Console::WriteLine();   
   }   
}

// The example displays the following output:
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       œil starts with oe: True (CurrentCulture comparison)
//       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
//       œil starts with oe: True (InvariantCulture comparison)
//       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
//       œil starts with oe: False (Ordinal comparison)
//       œil starts with oe: False (OrdinalIgnoreCase comparison)
//       
//       læring} starts with lae: True (CurrentCulture comparison)
//       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
//       læring} starts with lae: True (InvariantCulture comparison)
//       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
//       læring} starts with lae: False (Ordinal comparison)
//       læring} starts with lae: False (OrdinalIgnoreCase comparison)

using System;

public class Example
{
   public static void Main()
   {
      string[,] strings = { {"ABCdef", "abc" },                    
                            {"ABCdef", "abc" },  
                            {"œil","oe" },
                            { "læring}", "lae" } };
      for (int ctr1 = strings.GetLowerBound(0); ctr1 <= strings.GetUpperBound(0); ctr1++)
      {
            foreach (string cmpName in Enum.GetNames(typeof(StringComparison)))
            { 
               StringComparison strCmp = (StringComparison) Enum.Parse(typeof(StringComparison), 
                                                      cmpName);
               string instance = strings[ctr1, 0];
               string value = strings[ctr1, 1];
               Console.WriteLine("{0} starts with {1}: {2} ({3} comparison)", 
                                 instance, value, 
                                 instance.StartsWith(value, strCmp), 
                                 strCmp); 
            }
            Console.WriteLine();   
      }   
   }
}
// The example displays the following output:
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       œil starts with oe: True (CurrentCulture comparison)
//       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
//       œil starts with oe: True (InvariantCulture comparison)
//       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
//       œil starts with oe: False (Ordinal comparison)
//       œil starts with oe: False (OrdinalIgnoreCase comparison)
//       
//       læring} starts with lae: True (CurrentCulture comparison)
//       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
//       læring} starts with lae: True (InvariantCulture comparison)
//       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
//       læring} starts with lae: False (Ordinal comparison)
//       læring} starts with lae: False (OrdinalIgnoreCase comparison)

open System

let strings =
    array2D 
      [ [ "ABCdef"; "abc" ]
        [ "ABCdef"; "abc" ]
        [ "œil"; "oe" ]
        [ "læring}"; "lae" ] ]

for ctr1 = strings.GetLowerBound 0 to strings.GetUpperBound 0 do
    for cmpName in Enum.GetNames typeof<StringComparison> do
        let strCmp = Enum.Parse(typeof<StringComparison>, cmpName) :?> StringComparison
        let instance = strings[ctr1, 0]
        let value = strings[ctr1, 1]
        printfn $"{instance} starts with {value}: {instance.StartsWith(value, strCmp)} ({strCmp} comparison)"
    printfn ""
// The example displays the following output:
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//
//       œil starts with oe: True (CurrentCulture comparison)
//       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
//       œil starts with oe: True (InvariantCulture comparison)
//       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
//       œil starts with oe: False (Ordinal comparison)
//       œil starts with oe: False (OrdinalIgnoreCase comparison)
//
//       læring} starts with lae: True (CurrentCulture comparison)
//       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
//       læring} starts with lae: True (InvariantCulture comparison)
//       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
//       læring} starts with lae: False (Ordinal comparison)
//       læring} starts with lae: False (OrdinalIgnoreCase comparison)

Module Example
   Public Sub Main()
      Dim strings(,) As String = { {"ABCdef", "abc" },                    
                                   {"ABCdef", "abc" },  
                                   {"œil","oe" },
                                   { "læring}", "lae" } }
      For ctr1 As Integer = strings.GetLowerBound(0) To strings.GetUpperBound(0)
            For Each cmpName As String In [Enum].GetNames(GetType(StringComparison)) 
               Dim strCmp As StringComparison = CType([Enum].Parse(GetType(StringComparison), 
                                                      cmpName), StringComparison)
               Dim instance As String = strings(ctr1, 0)
               Dim value As String = strings(ctr1, 1)
               Console.WriteLine("{0} starts with {1}: {2} ({3} comparison)", 
                                 instance, value, 
                                 instance.StartsWith(value, strCmp), 
                                 strCmp) 
            Next
            Console.WriteLine()   
      Next   
   End Sub
End Module
' The example displays the following output:
'       ABCdef starts with abc: False (CurrentCulture comparison)
'       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (InvariantCulture comparison)
'       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (Ordinal comparison)
'       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
'       
'       ABCdef starts with abc: False (CurrentCulture comparison)
'       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (InvariantCulture comparison)
'       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (Ordinal comparison)
'       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
'       
'       œil starts with oe: True (CurrentCulture comparison)
'       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
'       œil starts with oe: True (InvariantCulture comparison)
'       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
'       œil starts with oe: False (Ordinal comparison)
'       œil starts with oe: False (OrdinalIgnoreCase comparison)
'       
'       læring} starts with lae: True (CurrentCulture comparison)
'       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
'       læring} starts with lae: True (InvariantCulture comparison)
'       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
'       læring} starts with lae: False (Ordinal comparison)
'       læring} starts with lae: False (OrdinalIgnoreCase comparison)

注解

方法 StartsWith 将 value 参数与此字符串开头的子字符串进行比较，并返回一个值，该值指示它们是否相等。 若要相等， value 必须是对此同一字符串的引用，必须是空字符串 (“”) ，或者必须与此字符串的开头匹配。 方法执行的 StartsWith 比较类型取决于 参数的值 comparisonType 。 此比较可以使用当前区域性 (StringComparison.CurrentCulture 和 StringComparison.CurrentCultureIgnoreCase) 的约定或固定区域性 (StringComparison.InvariantCulture 和 StringComparison.InvariantCultureIgnoreCase) ，也可以包含码位 (StringComparison.Ordinal 或 StringComparison.OrdinalIgnoreCase) 逐字符比较。 比较还可以区分大小写 (StringComparison.CurrentCulture、 StringComparison.InvariantCulture或 StringComparison.Ordinal) ，也可以忽略大小写 (StringComparison.CurrentCultureIgnoreCase、 StringComparison.InvariantCultureIgnoreCaseStringComparison.OrdinalIgnoreCase) 。

另请参阅

适用于

StartsWith(Char)

Source:
String.Comparison.cs
Source:
String.Comparison.cs
Source:
String.Comparison.cs

确定此字符串实例是否以指定字符开始。

public:
 bool StartsWith(char value);
public bool StartsWith (char value);
member this.StartsWith : char -> bool
Public Function StartsWith (value As Char) As Boolean

参数

value
Char

要比较的字符。

返回

Boolean

如果 true 与此字符串的开头匹配，则为 value；否则为 false。

注解

此方法执行区分大小写和不区分区域性的序号 () 比较。

适用于

StartsWith(String)

Source:
String.Comparison.cs
Source:
String.Comparison.cs
Source:
String.Comparison.cs

确定此字符串实例的开头是否与指定的字符串匹配。

public:
 bool StartsWith(System::String ^ value);
public bool StartsWith (string value);
member this.StartsWith : string -> bool
Public Function StartsWith (value As String) As Boolean

参数

value
String

要比较的字符串。

返回

Boolean

如果 true 与此字符串的开头匹配，则为 value；否则为 false。

例外

ArgumentNullException

value 为 null。

示例

以下示例定义一个 StripStartTags 方法，该方法使用 StartsWith(String) 方法从字符串开头删除 HTML 开始标记。 请注意， StripStartTags 方法以递归方式调用，以确保删除行开头的多个 HTML 开始标记。 该示例不会删除字符串中嵌入的 HTML 标记。

using namespace System;

String^ StripStartTags( String^ item )
{
   // Determine whether a tag begins the string.
   if (item->Trim()->StartsWith("<")) {
      // Find the closing tag.
      int lastLocation = item->IndexOf(">");
      
      // Remove the tag.
      if ( lastLocation >= 0 ) {
         item = item->Substring(lastLocation+ 1);
            
         // Remove any additional starting tags.
         item = StripStartTags(item);
      }      
   }

   return item;
}

int main()
{
   array<String^>^ strSource = { "<b>This is bold text</b>",
                   "<H1>This is large Text</H1>",
                   "<b><i><font color=green>This has multiple tags</font></i></b>",
                   "<b>This has <i>embedded</i> tags.</b>",
                   "<This line simply begins with a lesser than symbol, it should not be modified" };
   
   // Display the initial string array.
   Console::WriteLine("The original strings:");
   Console::WriteLine("---------------------");
   for each (String^ s in strSource)    
      Console::WriteLine( s );
   Console::WriteLine();

   Console::WriteLine( "Strings after starting tags have been stripped:");
   Console::WriteLine( "-----------------------------------------------");
   
   // Display the strings with starting tags removed.
   for each (String^ s in strSource)
      Console::WriteLine(StripStartTags(s));
}
// The example displays the following output:
//    The original strings:
//    ---------------------
//    <b>This is bold text</b>
//    <H1>This is large Text</H1>
//    <b><i><font color = green>This has multiple tags</font></i></b>
//    <b>This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified
//    
//    Strings after starting tags have been stripped:
//    -----------------------------------------------
//    This is bold text</b>
//    This is large Text</H1>
//    This has multiple tags</font></i></b>
//    This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified

using System;

public class Example
{
   public static void Main() {
      string [] strSource = { "<b>This is bold text</b>", "<H1>This is large Text</H1>",
                "<b><i><font color=green>This has multiple tags</font></i></b>",
                "<b>This has <i>embedded</i> tags.</b>",
                "<This line simply begins with a lesser than symbol, it should not be modified" };

      // Display the initial string array.
      Console.WriteLine("The original strings:");
      Console.WriteLine("---------------------");
      foreach (var s in strSource)
         Console.WriteLine(s);
      Console.WriteLine();

      Console.WriteLine("Strings after starting tags have been stripped:");
      Console.WriteLine("-----------------------------------------------");

      // Display the strings with starting tags removed.
     foreach (var s in strSource)
        Console.WriteLine(StripStartTags(s));
   }

   private static string StripStartTags(string item)
   {
      // Determine whether a tag begins the string.
      if (item.Trim().StartsWith("<")) {
         // Find the closing tag.
         int lastLocation = item.IndexOf( ">" );
         // Remove the tag.
         if (lastLocation >= 0) {
            item =  item.Substring( lastLocation + 1 );

            // Remove any additional starting tags.
            item = StripStartTags(item);
         }
      }

      return item;
   }
}
// The example displays the following output:
//    The original strings:
//    ---------------------
//    <b>This is bold text</b>
//    <H1>This is large Text</H1>
//    <b><i><font color = green>This has multiple tags</font></i></b>
//    <b>This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified
//
//    Strings after starting tags have been stripped:
//    -----------------------------------------------
//    This is bold text</b>
//    This is large Text</H1>
//    This has multiple tags</font></i></b>
//    This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified

let rec stripStartTags (item: string) =
    // Determine whether a tag begins the string.
    if item.Trim().StartsWith "<" then
        // Find the closing tag.
        let lastLocation = item.IndexOf ">"
        // Remove the tag.
        let item = 
            if lastLocation >= 0 then
                item.Substring( lastLocation + 1 )
            else 
                item

        // Remove any additional starting tags.
        stripStartTags item
    else
        item

let strSource = 
    [| "<b>This is bold text</b>"; "<H1>This is large Text</H1>"
       "<b><i><font color=green>This has multiple tags</font></i></b>"
       "<b>This has <i>embedded</i> tags.</b>"
       "<This line simply begins with a lesser than symbol, it should not be modified" |]

// Display the initial string array.
printfn "The original strings:"
printfn "---------------------"
for s in strSource do
    printfn $"{s}"
printfn ""

printfn "Strings after starting tags have been stripped:"
printfn "-----------------------------------------------"

// Display the strings with starting tags removed.
for s in strSource do
    printfn $"{stripStartTags s}"

// The example displays the following output:
//    The original strings:
//    ---------------------
//    <b>This is bold text</b>
//    <H1>This is large Text</H1>
//    <b><i><font color = green>This has multiple tags</font></i></b>
//    <b>This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified
//
//    Strings after starting tags have been stripped:
//    -----------------------------------------------
//    This is bold text</b>
//    This is large Text</H1>
//    This has multiple tags</font></i></b>
//    This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified

Public Class Example
   Public Shared Sub Main()
      Dim strSource() As String = { "<b>This is bold text</b>", 
                         "<H1>This is large Text</H1>", 
                         "<b><i><font color = green>This has multiple tags</font></i></b>", 
                         "<b>This has <i>embedded</i> tags.</b>", 
                         "<This line simply begins with a lesser than symbol, it should not be modified" }

      ' Display the initial string array.
      Console.WriteLine("The original strings:")
      Console.WriteLine("---------------------")
      For Each s In strSource
         Console.WriteLine(s)
      Next 
      Console.WriteLine()

      Console.WriteLine("Strings after starting tags have been stripped:")
      Console.WriteLine("-----------------------------------------------") 

      ' Display the strings with starting tags removed.
      For Each s In strSource
         Console.WriteLine(StripStartTags(s))
      Next 
   End Sub 

   Private Shared Function StripStartTags(item As String) As String
      ' Determine whether a tag begins the string.
      If item.Trim().StartsWith("<") Then
         ' Find the closing tag.
         Dim lastLocation As Integer = item.IndexOf(">")
         If lastLocation >= 0 Then
            ' Remove the tag.
            item = item.Substring((lastLocation + 1))
            
            ' Remove any additional starting tags.
            item = StripStartTags(item)
         End If
      End If
      
      Return item
   End Function 
End Class 
' The example displays the following output:
'    The original strings:
'    ---------------------
'    <b>This is bold text</b>
'    <H1>This is large Text</H1>
'    <b><i><font color = green>This has multiple tags</font></i></b>
'    <b>This has <i>embedded</i> tags.</b>
'    <This line simply begins with a lesser than symbol, it should not be modified
'    
'    Strings after starting tags have been stripped:
'    -----------------------------------------------
'    This is bold text</b>
'    This is large Text</H1>
'    This has multiple tags</font></i></b>
'    This has <i>embedded</i> tags.</b>
'    <This line simply begins with a lesser than symbol, it should not be modified

注解

此方法将此实例开头的子字符串进行比较 value ，该子字符串长度与 value相同，并返回它们是否相等的指示。 若要相等， value 必须是空字符串 (String.Empty) ，必须是对此同一实例的引用，或者必须与此实例的开头匹配。

此方法使用当前区域性执行单词 (区分大小写和区分区域性) 比较。

调用方说明

如 使用字符串的最佳做法中所述，建议避免调用替换默认值的字符串比较方法，而是调用需要显式指定参数的方法。 若要使用当前区域性的字符串比较规则确定字符串是否以特定子字符串开头，请通过调用StartsWith(String, StringComparison)方法重载（其comparisonType参数的 值为 CurrentCulture ）来显式指示你的意图。 如果不需要语言感知比较，请考虑使用 Ordinal。

另请参阅

适用于