Why are two identical strings not testing as equal?

Question

Hi,

My code:

stringFromRecievedData =
    [[NSString alloc]initWithData:_data1 encoding:NSUTF8StringEncoding];

if (![stringFromRecievedData isEqualToString:lastStringFromRecievedData]) {
    [lastStringFromRecievedData setString: stringFromRecievedData];

I get the same "not equal" result even in the second round- even when it is the same data each time...

Is this the correct way to compare the two?

Thanks.

Answer 1

If lastStringFromRecievedData is an instance of NSString (or subclass such as NSMutableString), then this is the correct way to compare two strings. In this case something else may be causing your strings to not be equal.

However, it looks like lastStringFromRecievedData is a some other object because you are calling setString: on it. If this is the case, you need to get the string from that object first.

stringFromRecievedData =
    [[NSString alloc]initWithData:_data1 encoding:NSUTF8StringEncoding];

// Assuming 'string' is the function to get the string from 'setString:' below
NSString *otherString = [lastStringFromRecievedData string];

if (![stringFromRecievedData isEqualToString:otherString]) {
    [lastStringFromRecievedData setString: stringFromRecievedData];

Answer 2

If all you're doing is looking to make sure your NSMutableString is equivalent to another NSString, why not do something like:

lastStringFromRecievedData = [stringFromRecievedData mutableCopy];

Or:

[lastStringFromRecievedData setString:stringFromRecievedData];

The end result will be the same.