What is the recommended way to append to NSString

Question

I am performing some string concatenation to create a database query. As part of this, I need to assign and re-assign NSString variable in order to append to it.

I am currently using this code:

NSString *retVal = [[NSString alloc]init];
NSString *concat = @"";
retVal = [NSString stringWithFormat:@"%@%@ myfield= 'myvalue'", retVal, concat];

Note that whenever retVal and concat hold "" (empty string), I get empty string back in retVal. This is definitely not expected as I should get " myfield= 'myvalue'".

What am I missing?

Update:

Here is last I tried:

NSMutableString * retVal =  [[NSMutableString alloc] init]; 
NSString * concat = @"";

[retVal appendString:@"appendstring"];


NSLog(@"%@", retVal); // prints <object returned empty description>  

[retVal appendString:concat];
[retVal appendString:@"appendstring1"];

NSLog(@"%@", retVal);  // prints %@

Answer 1

Either use an NSMutableString with appendString:, use stringByAppendingString:, or construct the full string with a single stringWithFormat:, plugging in the values you need all at once.

Answer 2

    NSString *retVal = @"";
    NSString *concat = @"";
    //do whatever stuff you want with retVal and concat 
    //once finished then do this below
    if(retVal.length==0||concat.length==0)
    {
    retVal = @"myfield= 'myvalue'";
    }
    else
    retVal = [NSString stringWithFormat:@"%@%@ myfield= 'myvalue'", retVal, concat];