本文由机器翻译。若要查看英语原文,请勾选“英语”复选框。 也可将鼠标指针移到文本上,在弹出窗口中显示英语原文。
翻译
英语

String.LastIndexOf 方法 (String, Int32, Int32)

 

报告指定字符串在此实例中的最后一个匹配项的从零开始的索引的位置。 搜索在指定字符位置的数目的字符串开始时,开始指定字符和其后面的位置。

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

public int LastIndexOf(
	string value,
	int startIndex,
	int count
)

参数

value
Type: System.String

要搜寻的字符串。

startIndex
Type: System.Int32

搜索起始位置。startIndex 此实例的开头开始搜索。

count
Type: System.Int32

要检查的字符位置数。

返回值

Type: System.Int32

如果找到该字符串,则为 value 的从零开始的起始索引位置;如果未找到该字符串或当前实例等于 String.Empty,则为 -1。 如果 valueEmpty,则返回值为 startIndex 和此实例中的最后一个索引位置中的较小者。

Exception Condition
ArgumentNullException

valuenull

ArgumentOutOfRangeException

count 为负数。

- 或 -

当前实例不等于 String.Empty,并且 startIndex 为负数。

- 或 -

当前实例不等于 String.Empty,并且 startIndex 大于此实例的长度。

- 或 -

当前实例不等于 String.Empty,并且 startIndex - count+ 1 指定不在此实例内的位置。

- 或 -

当前实例等于 String.Empty 并且 start 小于 -1 或大于零。

- 或 -

当前实例等于 String.Empty 并且 count 大于 1。

Index numbering starts from zero. That is, the first character in the string is at index zero and the last is at P:System.String.Length - 1.

The search begins at the startIndex character position of this instance and proceeds backward toward the beginning until either value is found or count character positions have been examined. For example, if startIndex is P:System.String.Length - 1, the method searches backward count characters from the last character in the string.

This method performs a word (case-sensitive and culture-sensitive) search using the current culture.

Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. If value consists only of one or more ignorable characters, the M:System.String.LastIndexOf(System.String,System.Int32,System.Int32) method always returns startIndex, which is the character position at which the search begins. In the following example, the M:System.String.LastIndexOf(System.String,System.Int32,System.Int32) method is used to find the position of a soft hyphen (U+00AD) in the two characters that precede the final "m" of two strings. Only one of the strings contains the required substring. If the example is run on the netfx40_short or later, in both cases, because the soft hyphen is an ignorable character, the method returns the index of "m" in the string when it performs a culture-sensitive comparison. Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m".

using System;

public class Example
{
   public static void Main()
   {
      int position = 0;
      string s1 = "ani\u00ADmal";
      string s2 = "animal";

      // Find the index of the soft hyphen.
      position = s1.LastIndexOf("m");
      Console.WriteLine("'m' at position {0}", position);
      if (position >= 0)
         Console.WriteLine(s1.LastIndexOf("\u00AD", position, position + 1));

      position = s2.LastIndexOf("m");
      Console.WriteLine("'m' at position {0}", position);
      if (position >= 0)   
         Console.WriteLine(s2.LastIndexOf("\u00AD", position, position + 1));

      // Find the index of the soft hyphen followed by "n".
      position = s1.LastIndexOf("m");
      Console.WriteLine("'m' at position {0}", position);
      if (position >= 0)
         Console.WriteLine(s1.LastIndexOf("\u00ADn", position, position + 1));

      position = s2.LastIndexOf("m");
      Console.WriteLine("'m' at position {0}", position);
      if (position >= 0)   
         Console.WriteLine(s2.LastIndexOf("\u00ADn", position, position + 1));

      // Find the index of the soft hyphen followed by "m".
      position = s1.LastIndexOf("m");
      Console.WriteLine("'m' at position {0}", position);
      if (position >= 0)
         Console.WriteLine(s1.LastIndexOf("\u00ADm", position, position + 1));

      position = s2.LastIndexOf("m");
      Console.WriteLine("'m' at position {0}", position);
      if (position >= 0)   
         Console.WriteLine(s2.LastIndexOf("\u00ADm", position, position + 1));
   }
}
// The example displays the following output:
//       'm' at position 4
//       4
//       'm' at position 3
//       3
//       'm' at position 4
//       1
//       'm' at position 3
//       1
//       'm' at position 4
//       4
//       'm' at position 3
//       3

调用函数说明:

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. To perform this operation by using the comparison rules of the current culture, call the M:System.String.LastIndexOf(System.String,System.Int32,System.Int32,System.StringComparison) method overload with a value of F:System.StringComparison.CurrentCulture for its comparisonType parameter.

The following example finds the index of all occurrences of a string in substring, working from the end of the substring to the start of the substring.

// Sample for String.LastIndexOf(String, Int32, Int32)
using System;

class Sample {
    public static void Main() {

    string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
    string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
    string str = "Now is the time for all good men to come to the aid of their party.";
    int start;
    int at;
    int count;
    int end;

    start = str.Length-1;
    end = start/2 - 1;
    Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, end);
    Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str);
    Console.Write("The string 'he' occurs at position(s): ");

    count = 0;
    at = 0;
    while((start > -1) && (at > -1))
        {
        count = start - end; //Count must be within the substring.
        at = str.LastIndexOf("he", start, count);
        if (at > -1) 
            {
            Console.Write("{0} ", at);
            start = at - 1;
            }
        }
    Console.Write("{0}{0}{0}", Environment.NewLine);
    }
}
/*
This example produces the following results:
All occurrences of 'he' from position 66 to 32.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The string 'he' occurs at position(s): 56 45
*/

通用 Windows 平台
自 8 起可用
.NET Framework
自 1.1 起可用
可移植类库
可移植 .NET 平台 中受支持
Silverlight
自 2.0 起可用
Windows Phone Silverlight
自 7.0 起可用
Windows Phone
自 8.1 起可用
返回页首
显示: