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As a newer programmer, I've discovered the magic of NSlog, and use it all through my code. It's been extremely helpful (along with NSZombieEnabled) in debugging.

I can see a definite performance hit on the simulator as it prints out all this stuff. I don't think I see any such hit on devices, but I'm not sure.

So does it cost anything to leave all the NSLogs in? Is it using more memory on the device? Or does the compiler just ignore them, like it does comments when I compile for a device?

EDIT:

Here's what I implemented, per the suggestion from rano.

In my App_Prefix.pch file, I added:

// DLog is almost a drop-in replacement for NSLog
// DLog();
// DLog(@"here");
// DLog(@"value: %d", x);
// Unfortunately this doesn't work DLog(aStringVariable); you have to do this instead     DLog(@"%@", aStringVariable);
#ifdef DEBUG
#   define DLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);
#else
#   define DLog(...)
#endif

// ALog always displays output regardless of the DEBUG setting
#define ALog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);

And then in my Project Info inspector, for the Debug configuration, under the heading GCC 4.2 - Preprocessing, I added the value DEBUG to the top entry called, Preprocessor Macros.

Works like a charm - DLog outputs when I build a Debug version and ALog always outputs.

Steve
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  • See also [Is it true that one should not use NSLog() on production code?](http://stackoverflow.com/questions/300673/is-it-true-that-one-should-not-use-nslog-on-production-code) – Brad Larson Nov 09 '10 at 00:55

3 Answers3

6

NSLog surely is more pricy than a simple printf but is a little more integrated into the objective-C and Cocoa framework.

By the way when you are seriously programming you will notice that it is unsufficient to most of your needs. Take a look at this article and its references to have an idea on how to replace it in a smart way.

In that way you can also have the compiler to ignore it when it is no more useful (e.g. when you will release your piece of code). In general you could #ifdef the calling to a log function in computing intensive loops/sequences of code.

rano
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    I just wanted to post the same link. Especially comment 15 by Bill Hollings is worth a look – Matthias Bauch Nov 08 '10 at 22:36
  • @fluchtpunkt yeah that headr is useful. Even though I prefer a shorter name for my logging function, something like `DNSLog` and in this way I can easily convert the previous ones – rano Nov 08 '10 at 22:39
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The answers above are outdated. You should simply use CocoaLumberjack is vastly superior to NSLog and provides much more functionality then the above answers.

dbainbridge
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NSLog is not implemented as a macro, so there will definitely be a cost. Quantifying it and deciding if it is important is harder. The only sure way to do that is to measure your own application.

Steven Fisher
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