Enable and Disable NSLog in DEBUG mode

57
votes

I want to enable NSLog when I am in debug and disable it otherwise. A very simple thing is:

#ifdef DEBUG
NSLog(@"My log");
#endif

But all this #ifdef and #endif is borring... :( So I try other thing: (.pch is good place to put it)

#ifdef DEBUG
#   define NSLog(text) NSLog(text);
#else 
#   define NSLog(text) 
#endif

This work very fine (isn't recursive). But the problem is that NSLog have infinite arguments.

void NSLog(NSString *format, ...)

How I solve this to work in preprocessor mode?

-- Edit --

This code make your NSLog better: 

#ifdef DEBUG
    #define NSLog(FORMAT, ...) fprintf(stderr,"%s\n", [[NSString stringWithFormat:FORMAT, ##__VA_ARGS__] UTF8String]);
#else
    #define NSLog(...)
#endif
5
objective-ccocoanslog
+1 for Nice Question. A complete reusable component on this topic at mobile.tutsplus.com/tutorials/iphone/… - Md Mahbubur Rahman
I follow the guide in the link. But I got the following compile error: Undefined symbols for architecture x86_64: ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) Please help @MahbuburRAaman - Gon
@Gon, Error Undefined symbols for architecture x86_64: ld: symbol(s) not found for architecture x86_64 appears for several reason. For example, for missing library or other cases, have a look at the following SO resource stackoverflow.com/questions/18408531/…, stackoverflow.com/questions/11996227/… , stackoverflow.com/questions/6231368/…. - Md Mahbubur Rahman
@MahbuburRAaman Thanks for replying. I've found the reason is I'm calling this custom NSLog method from a objective c++ file. - Gon
Please, where have I to place this code? - Ne AS

5 Answers

108
votes

This should do the trick:

 #ifdef DEBUG
 #   define NSLog(...) NSLog(__VA_ARGS__)
 #else 
 #   define NSLog(...) (void)0
 #endif
19
votes

This is a bit shorter and also disables NSLog when using a device. If you're writing a game, NSLogs sent often can reduce your FPS from 60 to 20.

#if !defined(DEBUG) || !(TARGET_IPHONE_SIMULATOR)
    #define NSLog(...)
#endif
8
votes

All the above answers are correct. I can suggest you to do it in a following way also. Suppose i have a if statement with no brackets

if(x==5)
NSLog("x is 5");

What will happen if it will replace NSLog with no statement. So we can simply replace it with an empty loop. 

#ifdef DEBUG
#define NSLog(...) NSLog(__VA_ARGS__)
#else
#define NSLog(...) do {} while (0)
#endif

This statement will run an empty loop once. This will safely remove your NSLog from all of your live code.

1
votes
#ifndef Debug
    #define Debug 1
#endif

#if Debug
#   define DebugLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);
#else
#   define DebugLog(...)
#endif

Set Debug to 1 for enabling the log and 0 for disabling it.

1
votes

Here is a nice trick... add to any .m

#define EXTRANSLog if([[NSUserDefaults standardUserDefaults] boolForKey:@"SomeFancyKey"] == YES) NSLog

Replace any 

NSLog(@"????");

with 

EXTRANSLog(@"????");

In this example, I created a NSUser key and set the BOOL to YES,, use some form of switch etc to change the key to NO or remove altogether if you don't want to view the EXTRANSLog's via console debugger.

I use this when troubleshooting and don't want all the excessive logs to appear. Only when SomeFancyKey == YES.

This is the same as 

#define NSLog if(1) NSLog

where 1 is YES show NSLog, and 0 is NO.