NSString的几个方法（rangeOfString，hasPrefix，hasSuffix，改变大小写...）

//忽略大小写进行比较，返回值与compare一样  
   result = [str1 caseInsensitiveCompare:str2];  
   if (result == NSOrderedAscending) {  
       NSLog(@"右边 > 左边");  
   }else if(result == NSOrderedSame){  
       NSLog(@"内容相同");  
   }else if (result == NSOrderedDescending){  
       NSLog(@"左边 > 右边");  
   } 

//拓展名  
        //获取拓展名,不带.  
        NSString *str2 = @"Users/CentralPerk/Desktop/test.txt";  
        NSLog(@"%@",[str2 pathExtension]);  
        //添加拓展名,不需要带.  
        NSLog(@"%@",[str2 stringByAppendingPathExtension:@"mp3"]);  
        //删除拓展名,带.一块删除  
        NSLog(@"%@",[str2 stringByDeletingPathExtension]); 

        //字符串的截取  
        NSString *str = @"123456789";  
        NSLog(@"%@",[str substringFromIndex:3]);  
        NSLog(@"%@",[str substringToIndex:6]);  
        NSLog(@"%@",[str substringWithRange:NSMakeRange(3, 3)]);  
          
        //用指定字符串分割字符串，返回一个数组  
        NSArray *array = [@"1,2,3,4,5,6" componentsSeparatedByString:@","];  
        NSLog(@"%@",array);  
          
        //将数组中的字符串组合成一个文件路径  
        NSMutableArray *components = [NSMutableArray array];  
        [components addObject:@"Users"];  
        [components addObject:@"CentralPerk"];  
        [components addObject:@"Desktop"];  
        NSString *path = [NSString pathWithComponents:components];  
        NSLog(@"%@",path);  //Users/CentralPerk/Desktop  
          
        //将一个路径分割成一个数组  
        NSArray *array1 = [path pathComponents];  
        NSLog(@"%@",array1);  
          
        //判断是否为绝对路径(依据：是否以‘/‘开始)  
        path = @"/Users/CentralPerk/Desktop";  
        NSLog(@"%i",[path isAbsolutePath]);  
          
        //获取最后一个目录  
        NSLog(@"%@",[path lastPathComponent]);  
          
        //删除最后一个目录  
        NSLog(@"%@",[path stringByDeletingLastPathComponent]);  
          
        //拼接一个目录  
        NSLog(@"%@",[path stringByAppendingPathComponent:@"aaa"]);   ///Users/CentralPerk/Desktop/aaa  
        NSLog(@"%@",[path stringByAppendingString:@"aaa"]);      ///Users/CentralPerk/Desktopaaa  
        NSLog(@"%@",[path stringByAppendingFormat:@"%@%@",@"b",@"c"]);  ///Users/CentralPerk/Desktopbc