Getting a function name (__func__) from a class T and a pointer to member function void(T::*pmf)()

Question

Is it possible to write some f() template function that takes a type T and a pointer to member function of signature void(T::*pmf)() a

Answer 1

TL;DR: It is not possible to do this in a reasonably portable way, other than using macros. Using debug symbols is really a hard solution, which will introduce a maintenance and architecture problem in the future, and a bad solution.

The names of functions, in any form, is not guaranteed to be stored in the binary [or anywhere else for that matter]. Static free functions certainly won't have to expose their name to the rest of the world, and there is no real need for virtual member functions to have their names exposed either (except when the vtable is formed in A.c and the member function is in B.c).

It is also entirely permissible for the linker to remove ALL names of functions and variables. Names MAY be used by shared libraries to find functions not present in the binary, but the "ordinal" way can avoid that too, if the system is using that method.

I can't see any other solution than making assert_test a macro - and this is actually a GOOD use-case of macros. [Well, you could of course pass __func__ as a an argument, but that's certainly NOT better than using macros in this limited case].

Something like:

#define assert_test(x, y)  do_assert_test(x, y, __func__)

and then implment do_assert_test to do what your original assert_test would do [less the impossible bit of figuring out the name of the function].

If it's unit tests, and you can be sure that you will always do this with debug symbols, you could solve it in a very non-portable way by building with debug symbols and then using the debug interface to find the name of the function you are currently in. The reason I say it's non-portable is that the debug API for a given OS is not standard - Windows does it one way, Linux another, and I'm not sure how it works in MacOS - and to make matters worse, my quick search on the subject seems to indicate that reading debug symbols doesn't have an API as such - there is a debug API that allows you to inspect the current process and figure out where you are, what the registers contain, etc, but not to find out what the name of the function is. So that's definitely a harder solution than "convince whoever needs to be convinced that this is a valid use of a macro".

Answer 2

It seems like what you are trying to achieve, is to get the name of the calling function in assert_test(). With gcc you can use backtace to do that. Here is a naive example:

#include <iostream>
#include <execinfo.h>
#include <cxxabi.h>

namespace unit_test 
{
struct test {};
}

std::string get_my_caller()
{
    std::string caller("???");
    void *bt[3];                             // backtrace
    char **bts;                              // backtrace symbols
    size_t size = sizeof(bt)/sizeof(*bt);
    int ret = -4;

    /* get backtrace symbols */
    size = backtrace(bt, size);
    bts = backtrace_symbols(bt, size);

    if (size >= 3) {
        caller = bts[2];

        /* demangle function name*/
        char *name;
        size_t pos = caller.find('(') + 1;
        size_t len = caller.find('+') - pos;

        name = abi::__cxa_demangle(caller.substr(pos, len).c_str(), NULL, NULL, &ret);

        if (ret == 0)
            caller = name;

        free(name);
    }

    free(bts);

    return caller;
}

void assert_test(bool expression, const std::string& message)
{
    if (!expression)
        std::cout << "ASSERTION FAILED " << get_my_caller() << ": " <<  message << std::endl;
}


struct my_test_case : public unit_test::test 
{
    void some_test()
    {
        assert_test(false, "test failed.");
    }
};

int main() 
{
    my_test_case tc;
    tc.some_test();

    return 0;
}

Compiled with:

g++ -std=c++11 -rdynamic main.cpp -o main

Output:

ASSERTION FAILED my_test_case::some_test(): test failed.

Note: This is a gcc (linux, ...) solution, which might be difficult to port to other platforms!