How to print out the method name and line number and conditionally disable NSLog?

Question

I'm doing a presentation on debugging in Xcode and would like to get more information on using NSLog efficiently.

In particular, I have two questions:

• is there a way to easily NSLog the current method's name / line number?
• is there a way to "disable" all NSLogs easily before compiling for release code?

Answer 1

Here are some useful macros around NSLog I use a lot:

#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__)

The DLog macro is used to only output when the DEBUG variable is set (-DDEBUG in the projects's C flags for the debug confirguration).

ALog will always output text (like the regular NSLog).

The output (e.g. ALog(@"Hello world") ) will look like this:

-[LibraryController awakeFromNib] [Line 364] Hello world

Answer 2

I've taken DLog and ALog from above, and added ULog which raises a UIAlertView message.

To summarize:

• DLog will output like NSLog only when the DEBUG variable is set
• ALog will always output like NSLog
• ULog will show the UIAlertView only when the DEBUG variable is set
  

#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__);
#ifdef DEBUG
#   define ULog(fmt, ...)  { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"%s\n [Line %d] ", __PRETTY_FUNCTION__, __LINE__] message:[NSString stringWithFormat:fmt, ##__VA_ARGS__]  delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil]; [alert show]; }
#else
#   define ULog(...)
#endif

This is what it looks like:

+1 Diederik

Answer 3

NSLog(@"%s %d %s %s", __FILE__, __LINE__, __PRETTY_FUNCTION__, __FUNCTION__);

Outputs file name, line number, and function name:

/proj/cocoa/cdcli/cdcli.m 121 managedObjectContext managedObjectContext

__FUNCTION__ in C++ shows mangled name __PRETTY_FUNCTION__ shows nice function name, in cocoa they look the same.

I'm not sure what is the proper way of disabling NSLog, I did:

#define NSLog

And no logging output showed up, however I don't know if this has any side effects.