NSLog the method name with Objective-C in iPhone

Question

Currently, we are defining ourselves an extended log mechanism to print out the class name and the source line number of the log.

#define NCLog(s, ...) NSLog(@"<%@:%d> %@", [[NSString stringWithUTF8String:__FILE__] lastPathComponent], \
    __LINE__, [NSString stringWithFormat:(s), ##__VA_ARGS__])

For example, when I call NCLog(@"Hello world"); The output will be:

<ApplicationDelegate:10>Hello world

Now I also want to log out the method name like:

<ApplicationDelegate:applicationDidFinishLaunching:10>Hello world

So, this would make our debugging become easier when we can know which method is getting called. I know that we also have Xcode debugger but sometimes, I also want to do debugging by logging out.

In my last `iPhone` project, I actually did this manually. Would love to see the answer to this. — Jacob Relkin, May 05 '10 at 02:46
Possible duplicate: http://stackoverflow.com/questions/969130/how-to-print-out-the-method-name-and-line-number-and-conditionally-disable-nslog — erkanyildiz, May 07 '14 at 14:03

score 272 · Accepted Answer · edited Aug 29 '17 at 05:26

272

print(__FUNCTION__) // Swift
NSLog(@"%@", NSStringFromSelector(_cmd)); // Objective-C

Swift 3 and above

print(#function)

edited Aug 29 '17 at 05:26

Irfan

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answered May 05 '10 at 02:46

drawnonward

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You really should use `NSLog(@"%@", NSStringFromSelector(_cmd))`, if you're going to use `_cmd`, since AFAIK Apple declares `_cmd` as type `SEL`, not a C-string. Just because it happens to be implemented as a C-string (as of the current versions of Mac OS X and the iPhone OS) doesn't mean you should use it in that way, since Apple could change it in an OS update. – Nick Forge May 05 '10 at 08:06
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Yes, NSStringFromSelector is the more correct answer. I never use _cmd as c string for anything but debug code. – drawnonward May 06 '10 at 00:17
Wow, the compiler complaints about pointer incompatibility, but it works... So _cmd (type: SEL) **really is** a char* !? – Nicolas Miari Jun 19 '12 at 09:46
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Method calls like `[self doSomething:arg1 somethingElse:arg2]` get converted into the C function call `objc_msgSend(self, "doSomething:somethingElse:, arg1, arg2);`. The second parameter of `objc_msgSend()` takes a `char*`. Remember that because the Objective-C runtime is dynamic, it's actually using a lookup table to figure out which method on which class to call so a char* is convenient since methods are represented as strings in the lookup table. – Jack Lawrence Nov 07 '12 at 16:42
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For Swift 2.2 should use `print("\(#function)")` – Jake Lin Mar 29 '16 at 05:43

score 165 · Answer 2 · answered May 05 '10 at 03:17

165

To technically answer your question, you want:

NSLog(@"<%@:%@:%d>", NSStringFromClass([self class]), NSStringFromSelector(_cmd), __LINE__);

Or you could also do:

NSLog(@"%s", __PRETTY_FUNCTION__);

answered May 05 '10 at 03:17

Dave DeLong

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With `__FUNCTION__` and its pretty equivalent also being available in C-functions. – Georg Fritzsche May 05 '10 at 03:21
N.B. `__FUNCTION__` also includes the class name – OrangeDog Mar 07 '14 at 10:26
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is there any difference using NSLog(@"%s",**__func__**); OR NSLog(@"%s", **__PRETTY_FUNCTION__**) ??? – Ravi Apr 10 '18 at 10:35

score 86 · Answer 3 · edited May 23 '17 at 11:46

tl;dr

NSLog( @"ERROR %@ METHOD %s:%d ", @"DescriptionGoesHere", __func__, __LINE__ );

Details

Apple has a Technical Q&A page: QA1669 - How can I add context information - such as the current method or line number - to my logging statements?

To assist with logging:

The C preprocessor provides a few macros.
Objective-C provides expressions (methods).
- Pass the implicit argument for the current method's selector: _cmd

As other answers indicated, to merely get the current method's name, call:

NSStringFromSelector(_cmd)

To get the current method name and current line number, use these two macros __func__ and __LINE__ as seen here:

NSLog(@"%s:%d someObject=%@", __func__, __LINE__, someObject);

Another example… Snippets of code I keep in Xcode's Code Snippet Library:

NSLog( @"ERROR %@ METHOD %s:%d ", @"DescriptionGoesHere", __func__, __LINE__ );

…and TRACE instead of ERROR…

NSLog( @"TRACE %@ METHOD %s:%d ", @"DescriptionGoesHere", __func__, __LINE__ );

…and a longer one using a soft-coded description passing a value ([rows count])…

NSLog( @"TRACE %@ METHOD %s:%d.", [NSString stringWithFormat:@"'Table of Contents.txt' file's count of Linefeed-delimited rows: %u.", [rows count]] , __func__, __LINE__ );

Preprocessor macros for logging

Note the use of a pair of underscore characters around both sides of the macro.

| Macro                | Format   | Description
  __func__               %s         Current function signature
  __LINE__               %d         Current line number
  __FILE__               %s         Full path to source file
  __PRETTY_FUNCTION__    %s         Like __func__, but includes verbose
                                    type information in C++ code.

Expressions for logging

| Expression                       | Format   | Description
  NSStringFromSelector(_cmd)         %@         Name of the current selector
  NSStringFromClass([self class])    %@         Current object's class name
  [[NSString                         %@         Source code file name
    stringWithUTF8String:__FILE__]   
    lastPathComponent] 
  [NSThread callStackSymbols]        %@         NSArray of stack trace

Logging Frameworks

Some logging frameworks may help with getting current method or line number as well. I'm not sure, as I've used a great logging framework in Java (SLF4J + LogBack) but not Cocoa.

See this question for links to various Cocoa logging frameworks.

Name of Selector

If you have a Selector variable (a SEL), you can print its method name ("message") in either of two ways as described by this Codec blog post:

Using Objective-C call to NSStringFromSelector:
NSLog(@"%@", NSStringFromSelector(selector) );
Using straight C:
NSLog(@"%s", selector );

This information drawn from the linked Apple doc page as of 2013-07-19. That page had been last updated 2011-10-04.

For C, use `sel_getName(SEL)` since SEL is an opaque type and might not always be a `char *` — Ethan Reesor, Dec 03 '13 at 00:31

Huynh Inc · Answer 4 · 2016-01-03T03:52:59.853

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NSLog(@"%@", NSStringFromSelector(_cmd)); // Objective-C
print(__FUNCTION__) // Swift

edited Jan 03 '16 at 03:52

answered Oct 25 '13 at 17:07

Huynh Inc

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For anyone who comes across this answer in the future: it is equivalent to the accepted answer, but the accepted answer was different, when this one was posted (the accepted answer was edited in 2014). I was about to down vote, but after a small investigation up voted instead :) – FreeNickname Apr 30 '15 at 05:20

score 0 · Answer 5 · answered Mar 03 '16 at 21:37

0

It's actually just as simple as:

printf(_cmd);

For some reason iOS allows _cmd to be passed as a literal char with not even a compile warning. Who knows

answered Mar 03 '16 at 21:37

Albert Renshaw

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score 0 · Answer 6 · answered Oct 12 '17 at 19:39

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In Swift 4:

func test(){

print(#function)

}

test() //print the value "test()"

answered Oct 12 '17 at 19:39

garg

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