oc-Foundation框架-NSMutableString－常用方法

 NSMutableString * str=  [[NSMutableString alloc]initWithCapacity:10];
    [str setString:@"1234"];//设置一个字符串
    [str appendString:@"aaaa"];
    [str appendFormat:@"%d",27]; //拼接字符串
    NSRange range= [str rangeOfString:@"aaa"];//快速取得一个字符串的范围
    [str replaceCharactersInRange:range withString:@"ddggggg"];//替换一个范围的字符串
    [str insertString:@"vvvv" atIndex:4];//插入一个字符串
    [str deleteCharactersInRange:range];//删除一个范围的字符串