NSMutableString *mstr =[NSMutableString stringWithFormat: @ "sfswswfgs"];

        //[mstr appendString: @ "123"];

        [mstr stringByAppendingString: @ "123"]; //没有追加

        NSLog(@"%@",mstr);

为什么用stringByAppendingString没有追加字符串，appendString可以？

1.     [mstr appendString: @ "123"];  //appendString不返回对象- (void)appendString:(NSString *)aString;
   
2.    
   
3.     [mstr stringByAppendingString: @ "123"]; //没有追加
   
4.    
   
5.     //strstringByAppendingString返回一个新的对象。看他的声明
   
6.     //- (NSString *)stringByAppendingString:(NSString *)aString;
   
7.    
   
8.     NSString *mstr1 =[mstr stringByAppendingString: @ "123"];
   
9.    
   
10.     NSLog(@"%@",mstr1);

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