NSLog tips and tricks

Question

Hi,

I'm doing a presentation on debugging in Xcode and would like to get more information on using NSLog efficiently. I'd like to know if there are any tips and tricks to using NSLog which you guys have picked up.

For example,

• 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?

Any other tips would be appreciated.

Thanks.

Answer 1

NSLog(@"%s %d %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.

Answer 2

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 3

My answer to this question might help, looks like it's similar to the one Diederik cooked up. You may also want to replace the call to NSLog() with a static instance of your own custom logging class, that way you can add a priority flag for debug/warning/error messages, send messages to a file or database as well as the console, or pretty much whatever else you can think of.

#define DEBUG_MODE

#ifdef DEBUG_MODE
    #define DebugLog( s, ... ) NSLog( @"<%p %@:(%d)> %@", self, [[NSString stringWithUTF8String:__FILE__] lastPathComponent], __LINE__, [NSString stringWithFormat:(s), ##__VA_ARGS__] )
#else
    #define DebugLog( s, ... ) 
#endif

Answer 4

To complement the answers above, it can be quite useful to use a replacement for NSLog in certain situations, especially when debugging. For example, getting rid of all the date and process name/id information on each line can make output more readable and faster to boot.

The following link provides quite a bit of useful ammo for making simple logging much nicer.

http://cocoaheads.byu.edu/wiki/a-different-nslog

Answer 5

Here one big collection of debug constants that we use. Enjoy.

// Uncomment the defitions to show additional info.

//  #define DEBUG

//  #define DEBUGWHERE_SHOWFULLINFO

//  #define DEBUG_SHOWLINES
//  #define DEBUG_SHOWFULLPATH
//  #define DEBUG_SHOWSEPARATORS
//  #define DEBUG_SHOWFULLINFO


// Definition of DEBUG functions. Only work if DEBUG is defined.
#ifdef DEBUG 

    #define debug_separator() NSLog( @"────────────────────────────────────────────────────────────────────────────" );

    #ifdef DEBUG_SHOWSEPARATORS
     #define debug_showSeparators() debug_separator();
    #else
     #define debug_showSeparators()
    #endif

    /// /// /// ////// ///// 

    #ifdef DEBUG_SHOWFULLPATH
     #define debug_whereFull() debug_showSeparators(); NSLog(@"Line:%d : %s : %s", __LINE__,__FILE__,__FUNCTION__); debug_showSeparators(); 
    #else
     #define debug_whereFull() debug_showSeparators(); NSLog(@"Line:%d : %s : %s", __LINE__,[ [ [ [NSString alloc] initWithBytes:__FILE__ length:strlen(__FILE__) encoding:NSUTF8StringEncoding] lastPathComponent] UTF8String ] ,__FUNCTION__); debug_showSeparators(); 
    #endif

    /// /// /// ////// ///// 

    #define debugExt(args,...) debug_separator(); debug_whereFull(); NSLog( args, ##__VA_ARGS__); debug_separator();

    /// /// /// ////// ///// Debug Print Macros

    #ifdef DEBUG_SHOWFULLINFO
     #define debug(args,...) debugExt(args, ##__VA_ARGS__);
    #else
     #ifdef DEBUG_SHOWLINES
      #define debug(args,...) debug_showSeparators(); NSLog([ NSString stringWithFormat:@"Line:%d : %@", __LINE__, args ], ##__VA_ARGS__); debug_showSeparators();
     #else
      #define debug(args,...) debug_showSeparators(); NSLog(args, ##__VA_ARGS__); debug_showSeparators();
     #endif
    #endif

    /// /// /// ////// ///// Debug Specific Types

    #define debug_object( arg ) debug( @"Object: %@", arg );
    #define debug_int( arg ) debug( @"integer: %i", arg );
    #define debug_float( arg ) debug( @"float: %f", arg );
    #define debug_rect( arg ) debug( @"CGRect ( %f, %f, %f, %f)", arg.origin.x, arg.origin.y, arg.size.width, arg.size.height );
    #define debug_point( arg ) debug( @"CGPoint ( %f, %f )", arg.x, arg.y );
    #define debug_bool( arg )  debug( @"Boolean: %@", ( arg == YES ? @"YES" : @"NO" ) );

    /// /// /// ////// ///// Debug Where Macros

    #ifdef DEBUGWHERE_SHOWFULLINFO
     #define debug_where() debug_whereFull(); 
    #else
     #define debug_where() debug(@"%s",__FUNCTION__); 
    #endif

    #define debug_where_separators() debug_separator(); debug_where(); debug_separator();

    /// /// /// ////// /////

#else
    #define debug(args,...) 
    #define debug_separator()  
    #define debug_where()   
    #define debug_where_separators()  
    #define debug_whereFull()   
    #define debugExt(args,...)
    #define debug_object( arg ) 
    #define debug_int( arg ) 
    #define debug_rect( arg )  
    #define debug_bool( arg )  
    #define debug_point( arg )
    #define debug_float( arg )
#endif