Enable and Disable NSLog in DEBUG mode

Question

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

+1 for Nice Question. A complete reusable component on this topic at http://mobile.tutsplus.com/tutorials/iphone/customize-nslog-for-easier-debugging/ — Md Mahbubur Rahman, Aug 18 '13 at 04:42
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, Dec 02 '13 at 03:19
@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 http://stackoverflow.com/questions/18408531/xcode-build-failure-undefined-symbols-for-architecture-x86-64, http://stackoverflow.com/questions/11996227/undefined-symbols-for-architecture-x86-64-in-objective-c , http://stackoverflow.com/questions/6231368/objective-c-undefined-symbol-compilation-error. — Md Mahbubur Rahman, Dec 02 '13 at 13:54
@MahbuburRAaman Thanks for replying. I've found the reason is I'm calling this custom NSLog method from a objective c++ file. — Gon, Dec 02 '13 at 14:17

JustSid · Accepted Answer · 2016-08-21T06:25:40.433

109

This should do the trick:

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

edited Aug 21 '16 at 06:25

answered Jul 01 '11 at 19:06

JustSid

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It's fine but replace # define NSLog(...) NSLog(__VA_ARGS__); with # define NSLog(...) NSLog(__VA_ARGS__) (remove last ;) – anatoliy_v Dec 03 '12 at 12:23
@JustSid: How do I set or reset the DEBUG flag? – Rashmi Ranjan mallick Sep 08 '15 at 06:04
This doesn't play nice with the ternary operator. – Stian Høiland Aug 20 '16 at 22:11
2

@StianHøiland While it's questionable wether ternary operator around void is a good idea to begin with, I've updated the code so that it does support it. – JustSid Aug 21 '16 at 06:26

score 19 · Answer 2 · answered Jan 12 '12 at 14:17

19

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

answered Jan 12 '12 at 14:17

Aram Kocharyan

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NaXir · Answer 3 · 2015-04-28T11:28:48.560

8

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.

edited Apr 28 '15 at 11:28

answered Jun 13 '14 at 18:09

NaXir

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Good point, and that’s also a good place to repeat that using `if` statements without brackets is probably a bad idea in the first place. – Vincent Tourraine Aug 03 '14 at 15:59
12

the code will be preprocessed to `if (x==5) ;` which is fine. – Matthias Bauch Aug 04 '14 at 08:45
This doesn't play nice with the ternary operator. – Stian Høiland Aug 20 '16 at 22:11
if you have a common constants file that is included in .pch then place in that, otherwise you can place it at top of class before @implementation – NaXir Mar 23 '17 at 05:54

score 1 · Answer 4 · answered Apr 10 '15 at 07:05

1

#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.

answered Apr 10 '15 at 07:05

Prashant

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You can create Constant Header file and add the code to it and for accessing you just need to the import the Header file and use the DebugLog function to log the variables you desire to.... – Prashant Mar 23 '17 at 11:57

score 1 · Answer 5 · answered Dec 24 '16 at 06:32

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.

Enable and Disable NSLog in DEBUG mode

5 Answers5

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