How to find out who called a method?

Question

Example: When my method -fooBar gets called, I want it to log in the console which other method of which other class called it.

Right now, I only know how to log the method name of fooBar itself and it's class, with this:

_cmd

[self class]

Is this possible to figure out?

score 35 · Accepted Answer · answered Nov 25 '09 at 01:07

In fully optimized code, there is no 100% surefire way to determine the caller to a certain method. The compiler may employ a tail call optimization whereas the compiler effectively re-uses the caller's stack frame for the callee.

To see an example of this, set a breakpoint on any given method using gdb and look at the backtrace. Note that you don't see objc_msgSend() before every method call. That is because objc_msgSend() does a tail call to each method's implementation.

While you could compile your application non-optimized, you would need non-optimized versions of all of the system libraries to avoid just this one problem.

And this is just but one problem; in effect, you are asking "how do I re-invent CrashTracer or gdb?". A very hard problem upon which careers are made. Unless you want "debugging tools" to be your career, I would recommend against going down this road.

What question are you really trying to answer?

@alexgray How is it an anti-answer? The answer is exactly precise in scope and scale of the problem and, given the acceptance and final question, hopefully led the OP down a path to success. — bbum, May 04 '13 at 06:37

score 7 · Answer 2 · edited May 23 '17 at 11:55

7

How about this:

NSString *sourceString = [[NSThread callStackSymbols] objectAtIndex:1];

NSCharacterSet *separatorSet = [NSCharacterSet characterSetWithCharactersInString:@" -[]+?.,"];
NSMutableArray *array = [NSMutableArray arrayWithArray:[sourceString  componentsSeparatedByCharactersInSet:separatorSet]];
[array removeObject:@""];

NSLog(@"Class caller = %@", [array objectAtIndex:3]);
NSLog(@"Method caller = %@", [array objectAtIndex:4]);

Credits to the original author, intropedro.

edited May 23 '17 at 11:55

Community

1
1

answered Feb 06 '14 at 19:31

Maxim Chetrusca

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4

That won't work in fully optimized code as tail-call optimizations make frames disappear entirely from the stack. – bbum May 13 '14 at 17:28

score 3 · Answer 3 · answered Nov 25 '09 at 00:54

3

It's not possible in the general case without actually walking the stack. There's not even a guarantee that another object send the message that called the method. For example, it could be called from a block in a signal handler.

answered Nov 25 '09 at 00:54

Chuck

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score 3 · Answer 4 · answered Aug 25 '16 at 10:18

3

NSLog(@"Show stack trace: %@", [NSThread callStackSymbols]);

answered Aug 25 '16 at 10:18

Dmitry A.

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score 2 · Answer 5 · answered Nov 25 '09 at 02:19

2

See backtrace(3).

answered Nov 25 '09 at 02:19

Peter Hosey

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score 2 · Answer 6 · answered Sep 04 '14 at 13:27

User the below method
Pass index for which you want to display method and pass -1 if you want to display full stack of method

+(void) methodAtIndex:(int)index{
    void* callstack[128];
    int frames = backtrace(callstack, 128);
    char** strs = backtrace_symbols(callstack, frames);

    if (index == -1) {
        for (int i = 0; i < frames; ++i) {
            printf("%s\n", strs[i]);
        }
    }
    else {
        if (index < frames) {
            printf("%s\n", strs[index]);
        }
    }
    free(strs);

}

I'm getting `error: warning: couldn't get cmd pointer (substituting NULL): no variable named '_cmd' found in this frame` — ReDetection, Nov 04 '14 at 05:37

score 1 · Answer 7 · answered Nov 25 '09 at 01:03

1

This information can be obtained using DTrace.

answered Nov 25 '09 at 01:03

arul

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score 1 · Answer 8 · answered Nov 25 '09 at 01:04

1

Make a macro that adds the __FUNCTION__ to the function name to the function call. This macro will then call your function with an extra parameter of a char* to the target function.

answered Nov 25 '09 at 01:04

Robert Deml

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That assumes that you have control over the caller and can change the ABI between caller and callee by changing the argumentation, which is rarely the case. – bbum Nov 25 '09 at 01:08

score 0 · Answer 9 · answered Feb 04 '15 at 14:05

I was trying to catch who, how and when changes window's size and did some handwork:

- (void)logWindowWidth:(NSString *)whoCalls {
   NSLog(@"%@", whoCalls);
   NSLog(@"self.window.size.width %f", self.window.size.width);
}

-(void)someMethod {
  [self logWindowWidth:@"someMethod - before"];
  ...
  [self logWindowWidth:@"someMethod - after"];
}

-(void)anotherMethod {
  [self logWindowWidth:@"anotherMethod - before"];
  ...
  [self logWindowWidth:@"anotherMethod - after"];
}

How to find out who called a method?

9 Answers9

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