How to know what function called another

Question

Hi,

I wanna know if there is any way to know where the function currently in execution was called, this is, in what file and line. I'm using C language, and I'm looking for something similar to _FUNCTION_, _LINE_ or _FILE_ macros.

Best regards, Sérgio

Answer 1

There's nothing in C itself that would give you this information. You could either trace the information yourself (upon entry/exit) or rely on platform specific APIs to walk the call stack and determine the calling function, but not much more.

Answer 2

If you need to know it at runtime, I don't think it's possible.

If you need to know it at debugtime, you can place a breakpoint on the function you want, and then, using GDB (using bt command) or Vistual Studio's debugger, inspect the current STACK TRACE.

Answer 3

__FILE__, __LINE__ etc are preprocessor macros which can easily be expanded to the correct value at compile time. A function may get called from many possible places, so that can't be done via the preprocessor. Finding out the caller's name would be very difficult; it involves walking the stack and matching addresses to symbols.

If you can live with a small hack, this might work (untested):

/* Add a called argument to your function */
void _myFunction(char *caller, int more_args)

/* And define a macro that adds it automagically */
#define myFunction(a) _myFunction(__FUNCTION__, a)

Answer 4

Rename your function

void Function(param1)
{
}

to

void Function_debug(param1, char * file, char * func, unsigned long line)
{
}

Then #define a macro like this:

#define Function(param1) Function_debug(param1, __FILE__, __FUNCTION__, __LINE__)

Answer 5

This is actually a bit more complicated to do. Your best bet is to get a backtrace on a debugger, or find something similar to pstack for your platform. The manual way would involve traversing the call stack and using debug symbols to translate that to files and lines.

Answer 6

You can use logs .

#define BEGIN_FUNC(X,Y,Z) printf("Function %s Entered at line %d from file %s",X,Z,Y)
#define END_FUNC(X)  printf("Function %s Exited at line %d from file %s",X,Z,Y)

foo()
{
BEGIN_FUNC(__func__,__FILE__,__LINE__);

//Your code here


END_FUNC(__func___FILE__,__LINE__);

}

OR

Use bt in gdb. I call it backtrace.

Answer 7

There isn't anything that is supported in all implementations that will do what you want. I have occasionally found myself in the same situation, where I needed to track callers for a few methods and did something like the following:

#ifdef TRACKBACK
int foo(int arg1, int arg2, const char * file, int line)
{
    SEND_TO_LOG("foo", file, line);
#else
int foo(int arg1, int arg2)
{
#endif
    ...
    ...

Of course, it makes for a bit of a headache at the calling end, so you'll want to do something like:

#ifdef TRACKBACK
    #define TRACKING, __FILE__, __LINE__
#else
    #define TRACKING
#endif

Then the call:

foo(arg1, arg2 TRACKING);  //note the lack of the comma

It does the trick when all else fails.