Comparison between point and integer ('int' and 'void *') using NULL

Question

I get the error message "Comparison between point and integer ('int' and 'void *') using NULL" before I run the application. The strange thing is the application runs perfect every time. Here is a snippet of the code.

- (IBAction) addButtonAction:(id)sender
{
    int timeStamp = nil;

    timeStamp = self.hourTextField.intValue;


    if (timeStamp == NULL) {
        NSLog(@"Nothing here for ya");
    }
    else {
        NSLog(@"monkey shit");
    }

}

I get the error at the line.

    if (timeStamp == NULL) {

Answer 1

NULL is meant to be used for pointer comparisons only. timeStamp is an int, not a pointer, so the comparison doesn't really make sense. The compiler sees the comparison with NULL and says, "maybe he thinks timeStamp is a pointer, but it's not, so I better warn him". In this case, you probably want to check that timeStamp is not zero:

if (timeStamp == 0) {
    NSLog(@"Nothing here for ya");
}

Indeed, that's actually what your code is doing now, because in reality NULL is 0.

Also worth noting is that the compiler is issuing a warning, not an error. The important difference is that warnings are things the compiler thinks might be a mistake, but which don't prevent the program from compiling. Errors actually prevent the compiler from doing its job, and cause compilation to fail. You should never ignore warnings. You can tell the compiler to treat warnings as errors, to enforce discipline on yourself.