NSMutableString 是NSString 的子类，NSMutableString有很多方法，下面是总结的几种常用的方法：

stringWithString:，类级构造方法创建NSString对象；

insertString:，插入字符串，不会创建新的对象；

appendString:，追加字符串，不会创建新的对象；

deleteCharactersInRange:，在一个范围内删除字符串，不会创建新的对象；

replaceCharactersInRange: withString:，替换字符串，不会创建新的对象。

#import 
    
       int main (int argc, const char * argv[]) {      NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];          NSString *str1 = @"Objective C";      NSString *search,*replace;      NSMutableString *mstr;      NSRange substr;            //从不可变的字符创建可变字符串对象      mstr = [NSMutableString stringWithString: str1];      NSLog(@" %@", mstr);            //插入字符串      [mstr insertString: @ " Java" atIndex: 9];      NSLog(@" %@", mstr);      //具有连接效果的插入字符串      [mstr insertString: @ " and C++"atIndex: [mstr length]];      NSLog(@" %@", mstr);      //字符串连接方法      [mstr appendString: @ " and C"];      NSLog(@" %@", mstr);          //使用NSRange删除字符串      [mstr deleteCharactersInRange:NSMakeRange(16, 13)];      NSLog(@" %@", mstr);          //查找字符串位置      substr = [mstr rangeOfString: @ "string B and"];      if (substr.location != NSNotFound) {               [mstr deleteCharactersInRange: substr];          NSLog(@" %@", mstr);      }      //直接设置可变字符串       [mstr setString: @ "This is string A "];      NSLog(@" %@", mstr);            [mstr replaceCharactersInRange: NSMakeRange(8, 8)                          withString: @ "a mutable string "];      NSLog(@" %@", mstr);      //查找和替换      search = @"This is ";      replace = @"An example of ";            substr = [mstr rangeOfString:search];            if (substr.location != NSNotFound) {          [mstr replaceCharactersInRange:substr withString: replace];          NSLog(@" %@", mstr);      }      //查找和替换所有的情况      search = @"a";      replace = @"X";      substr = [mstr rangeOfString: search];            while (substr.location != NSNotFound) {          [mstr replaceCharactersInRange:substr withString: replace];          substr = [mstr rangeOfString: search];      }      NSLog(@" %@", mstr);                [pool drain];          return 0;  }
    

运行结果如下：

2011-09-08 16:35:26.320 2.10.1-2[3124:a0f]  Objective C  2011-09-08 16:35:26.323 2.10.1-2[3124:a0f]  Objective Java C  2011-09-08 16:35:26.324 2.10.1-2[3124:a0f]  Objective Java C and C++  2011-09-08 16:35:26.324 2.10.1-2[3124:a0f]  Objective Java C and C++ and C  2011-09-08 16:35:26.325 2.10.1-2[3124:a0f]  Objective Java CC  2011-09-08 16:35:26.325 2.10.1-2[3124:a0f]  This is string A   2011-09-08 16:35:26.326 2.10.1-2[3124:a0f]  This is a mutable string    2011-09-08 16:35:26.326 2.10.1-2[3124:a0f]  An example of a mutable string    2011-09-08 16:35:26.327 2.10.1-2[3124:a0f]  An exXmple of X mutXble string

我们解释主要代码。语句[mstr deleteCharactersInRange:NSMakeRange(16, 13)]是删除指定范围的字符串，函数NSMakeRange 是创建NSRange结构体，其中第一个参数是位置，第二个参数是长度；语句[mstr replaceCharactersInRange: NSMakeRange(8, 8)withString: @ "a mutable string "]替换指定访问的字符串；语句[mstr deleteCharactersInRange: substr]是删除指定范围的字符串。