Is there a way to tell what line of code generates log output without using breakpoints and stepping in Xcode (iOS)?

Question

I have the following log outputs in Xcode:

2013-05-20 17:23:19.901 MyApp[2408:303] invalid pixel format
2013-05-20 17:23:19.901 MyApp[2408:303] invalid context

The problem is I don't know what line of code is generating these errors. I've tried walking through but it's extremely tedious considering the complexity of this part of my app. Is there a quick and simple way to track down the line of code that is outputting these?

Jeremy Fox · Accepted Answer · 2013-05-21 01:13:03Z

5

Yes, there is a way to do what you are asking. Simply add the following to your prefix header YourAppName-Prefix.pch.

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

That will override NSLog with a custom NSLog that will print like this:

2013-05-20 21:11:10.407 YourAppName[46526:c07] -[JFDepthView initWithGestureRecognizer:] [Line 81] JFDepthView Initialized!

It should also work for 3rd party libraries you've added to your project.

answered May 21, 2013 at 1:13

Jeremy Fox

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1 Comment

John Sauer Over a year ago

For me, adding this macro causes the build error Expected ')' to match this '(' in line 422 of NSObjCRuntime.h, where the NSLog function is declared. Am I doing something wrong?

zaph · Accepted Answer · 2013-05-21 00:54:41Z

2

From "C" documentation, Standard Predefined Macros - The C Preprocessor:

__FILE__ and __LINE__ are useful in generating an error message

NSLog(@"Line: %d", __LINE__);

answered May 21, 2013 at 0:54

zaph

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5 Comments

Ethan Allen Over a year ago

I'm not the one outputting the logs above with NSLog()... it's a generated error by the compiler/Xcode when the app is running. I need to know where it's generated.

rmaddy Over a year ago

@EthanAllen Neither Xcode or the compiler are outputting those messages. They would be generated by whatever library or framework they are coming from.

Ethan Allen Over a year ago

OK, that makes sense, but how do I know which library? And what line of code called into it? I'm only calling into Apple libraries.

HM1 Over a year ago

@Ethan, have you tried symbolic breakpoints? I don't know whether it would work because I've never tried it, but its what I would look into.

zaph Over a year ago

@HM If breakpoints were not ruled put a symbolic breakpoint with a condition should work well.

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