CODEWITHSUNDEEP
objective-cmacosnsstringnslog
SMoi
SMoi

Reputation: 13

NSLog prints a string different to the NSString with format

This is something that I'm truly baffled by: when I initialize a string with format with two different variables like this

Order *o = [orders objectAtIndex:i];
NSString *line = [[NSString alloc] initWithFormat:(@"%@;%@\n", [o _length], [o _amount])];

and then print it out with 

NSLog(@"%@", line);

it shows up like this:

tableviewtest[4812:123250] 200

Which is wrong. However if I do the same by doing this

NSLog(@"%@;%@\n", [o _length], [o _amount]);

it comes out like this:

tableviewtest[4812:123250] 120cm;200

Which is how I'd WANT the line to be. Why is this happening? I need it to be in the same format as the line so that I can then write it into a text file later.

EDIT:

_length and _amount are @property NSString *_length in an Order-class. orders is an NSMutableArray that houses the data to an NSTableView, where the data is put in with NSComboBoxes and NSTextFields. Compiler also gives a warning: Format string is not a string literal (potentially insecure).

Upvotes: 0

Views: 273

Answers (2)

Amin Negm-Awad
Amin Negm-Awad

Reputation: 16660

@Schemetrical is correct, but it is not a compiler confusion. It is a behavior defined in the C standard. Let's have the original source code:

NSString *line = [[NSString alloc] initWithFormat:(@"%@;%@\n", [o _length], [o _amount])];

The arg list is build from

(@"%@;%@\n", [o _length], [o _amount])

This is a expression build from comma operators following the C standard, 6.5.17.. That means that

@"%@;%@\n", [o _length]

is evaluated as

((void)@"%@;%@\n")
expr = [o _length]

returning expr. Then

(expr, [o _amount])

is evaluated as

((void)expr)
expr = [o _amount])

This is the result of the expression used as single argument:

NSString *line = [[NSString alloc] initWithFormat:_amount];

Therefore the whole statement is pretty good C/Objective-C code. The only reason to show a warning is that the format arg is not a constant. (But this is definitely not what went wrong.)

Upvotes: 2

Schemetrical
Schemetrical

Reputation: 5536

Instead of
NSString *line = [[NSString alloc] initWithFormat:(@"%@;%@\n", [o _length], [o _amount])];,
use
NSString *line = [NSString stringWithFormat:@"%@;%@\n", [o _length], [o _amount]];

Upvotes: 1

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