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NSLog output only when building in Debug Mode

This information can be found quite a few places online but I thought the information was a little scattered, so for my benefit and anyone else who might find this, I thought I’d do a quick and dirty how-to for getting some logging that only shows up when you build your project in debug mode. This is specific to the iPhone but I can’t imagine why you couldn’t re-factor it to work with any Xcode projects.

We’ll start by adding this to your application’s prefix file (should be named MyAppName_Prefix.pch.

#ifdef DEBUG
#define DLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);
#else
#define DLog(...)
#endif
#define ALog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);

Keeping with the quick and dirty thing, basically this just checks to see if DEBUG is defined somewhere and if it is it defines a preprocessor function called DLog(). DLog works just like NSLog() with only 3 exceptions.

• You can’t do DLog(someVariable);. Instead do DLog(@"%@",someVariable).
• The PRETTY_FUNCTION stuff adds some extra info about which class and the line number DLog was called from so you can easily find it in your code.
• You should only see log output while your app is built in Debug Mode.

We also define ALog() which works just like DLog but will always display and isn’t dependent on DEBUG.

Now all we have to do is define DEBUG in our project settings! Head into your Project Settings (Project -> Edit Project Settings) and in the BUILD tab, select Configuration: Debug and Show: Settings Defined At This Level. Add a User-Defined Setting and call it OTHER_CFLAGS. Set it’s value to -DDEBUG=1 and your all set.

Now you should only see any DLog calls when you build in Debug Mode! Like I said, this information is all around the web and I just wanted to kind of condense it all into a quick and dirty tutorial so I didn’t want to go into too much detail. If you want more information about how this is done, you check here and here for ALL the information I have here in much more detail. All the credit for the information here goes to those 2 posts.