Today I was debugging a tricky problem in an iOS app that only happened when I was not using the debugger. Due to some strange timing issue (that I have yet to figure out), stopping on breakpoints actually caused the problem to go away, no matter how quickly I clicked the debugger’s continue button. So how was I to find out what was wrong?
I decided that printing the name of the class and method that was being called might be a good idea. So I started with this naïve approach:
- (void)viewDidLoad
{
NSLog(@"MyViewController viewDidLoad");
// ...
}
Of course, adding this to each method that I wanted to debug was quickly going to get out of hand. I didn’t want to have to change the class name and method name in the string each time I copied and pasted my NSLog statement. So I went searching for a solution, came across this Stack Overflow question about logging Objective-C method names, and took a good long look at the accepted answer, which said to use this:
NSLog(@"%s" , _cmd);
But after reading the comments, looking over Apple’s Technical Q&A on the topic, and learning that the compiler flags that statement with a warning, I decided I didn’t like that approach. Since _cmd is defined as a SEL, Apple says to use it with NSStringFromSelector, like this:
NSLog(@"%@", NSStringFromSelector(_cmd));
This fixes the compiler warning, but now it doesn’t output what I want. Here’s what it spits out in the console:
viewDidLoad
Umm…yeah…not very useful. No class information. So it’s not at all helpful if I’m trying to see which class’s viewDidLoad was called. Moving further through the Technical Q&A (and the highest-voted Stack Overflow answer), I found…
The Best Way to Log Class and Method Names in Objective-C
NSLog(@"%s", __PRETTY_FUNCTION__);
…which when placed into a viewDidLoad like so…
- (void)viewDidLoad
{
NSLog(@"%s", __PRETTY_FUNCTION__);
// ...
}
…produces some lovely output in our console like this…
-[MyViewController viewDidLoad]
…which is exactly what I wanted.
So the PRETTY_FUNCTION preprocessor macro prints the class name, method name, and indicates whether it’s a class method or an instance method (for an added bonus!). And for a second added bonus, it’s easy to remember. Much easier than _cmd…
And there you have it – you can easily copy and paste this into each method you want to log without changing anything inside the NSLog statement.
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