String.StartsWith 方法 (String)

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本文介绍 .NET Framework 中 String 类的 StartsWith 方法，该方法用于判断字符串是否以特定字符开始。文章通过示例代码展示了如何使用此方法来移除字符串开头的 HTML 标签。

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.NET Framework 类库
String.StartsWith 方法 (String)
请参见示例

确定此实例的开头是否与指定的字符串匹配。

命名空间:System
程序集:mscorlib（在 mscorlib.dll 中）

语法
C#
public bool StartsWith (
string value
)

参数
value
要比较的 String。

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

异常
异常类型条件
ArgumentNullException
value 为空引用（在 Visual Basic 中为 Nothing）。

备注
此方法将 value 与位于此实例开头、与 value 长度相同的子字符串进行比较，并返回它们是否相等的指示。若要相等，value 必须是空字符串 (Empty)、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（区分大小写和区域性）比较。

示例
下面的代码示例说明了如何使用 StartsWith 方法。

C# 复制代码
using System;

public class EndsWithTest {
public static void Main() {

// process a string that contains html tags
// this sample does not remove embedded tags (tags in the middle of a line)

string [] strSource = { "This is bold text", "<H1>This is large Text</H1>",
 "This has multiple tags",
 "This has embedded tags.",
 "<This line simply begins with a lesser than symbol, it should not be modified" };

Console.WriteLine("The following lists the items before the tags have been stripped:");
Console.WriteLine("-----------------------------------------------------------------");

        // print out the initial array of strings
        foreach ( string s in strSource )
            Console.WriteLine( s );

Console.WriteLine();

Console.WriteLine("The following lists the items after the tags have been stripped:");
Console.WriteLine("----------------------------------------------------------------");

        // print out the array of strings
        foreach ( string s in strSource )
            Console.WriteLine( StripStartTags( s ) );
    }

private static string StripStartTags( string item ) {

// try to find a tag at the start of the line using StartsWith
if (item.Trim().StartsWith("<")) {

// now search for the closing tag...
int lastLocation = item.IndexOf( ">" );

            // remove the identified section, if it is a valid region
            if ( lastLocation >= 0 )
                item = item.Substring( lastLocation + 1 );
        }

return item;
}
}

C++ 复制代码
using namespace System;
using namespace System::Collections;
String^ StripStartTags( String^ item )
{

 // try to find a tag at the start of the line using StartsWith
 if ( item->Trim()->StartsWith( "<" ) )
 {

 // now search for the closing tag->->.
 int lastLocation = item->IndexOf( ">" );

 // remove the identified section, if it is a valid region
 if ( lastLocation >= 0 )
 item = item->Substring( lastLocation + 1 );
 }

return item;
}

int main()
{

 // process a string that contains html tags
 // this sample does not remove embedded tags (tags in the middle of a line)
 array<String^>^strSource = {"This is bold text","<H1>This is large Text</H1>","This has multiple tags","This has embedded tags.","<This line simply begins with a lesser than symbol, it should not be modified"};
 Console::WriteLine( "The following lists the items before the tags have been stripped:" );
 Console::WriteLine( "-----------------------------------------------------------------" );

 // print out the initial array of strings
 IEnumerator^ myEnum1 = strSource->GetEnumerator();
 while ( myEnum1->MoveNext() )
 {
 String^ s = safe_cast<String^>(myEnum1->Current);
 Console::WriteLine( s );
 }

Console::WriteLine();
 Console::WriteLine( "The following lists the items after the tags have been stripped:" );
 Console::WriteLine( "----------------------------------------------------------------" );

 // print [Out] the* array of strings
 IEnumerator^ myEnum2 = strSource->GetEnumerator();
 while ( myEnum2->MoveNext() )
 {
 String^ s = safe_cast<String^>(myEnum2->Current);
 Console::WriteLine( StripStartTags( s ) );
 }
}

JScript 复制代码
import System;

public class EndsWithTest {
public static function Main() : void {

// process a string that contains html tags
// this sample does not remove embedded tags (tags in the middle of a line)

var strSource : String [] = [ "This is bold text", "<H1>This is large Text</H1>",
 "This has multiple tags",
 "This has embedded tags.",
 "<This line simply begins with a lesser than symbol, it should not be modified" ];

Console.WriteLine("The following lists the items before the tags have been stripped:");
Console.WriteLine("-----------------------------------------------------------------");

        // print out the initial array of strings
        for( var i : int in strSource )
            Console.WriteLine( strSource[i] );

Console.WriteLine();

Console.WriteLine("The following lists the items after the tags have been stripped:");
Console.WriteLine("----------------------------------------------------------------");

        // print out the array of strings
        for ( i in strSource )
            Console.WriteLine( StripStartTags( strSource[i] ) );
    }

private static function StripStartTags( item : String ) : String {

// try to find a tag at the start of the line using StartsWith
if (item.Trim().StartsWith("<")) {

// now search for the closing tag...
var lastLocation : int = item.IndexOf( ">" );

            // remove the identified section, if it is a valid region
            if ( lastLocation >= 0 )
                item = item.Substring( lastLocation + 1 );
        }

return item;
}
}
EndsWithTest.Main();

平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition

.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。

版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0

.NET Compact Framework
受以下版本支持：2.0、1.0

请参见
参考
String 类
String 成员
System 命名空间
EndsWith