Question

When creating a template function in C++ is there a simple way to have the typename of the template represented as a string? I have a simple test case to show what I’m trying to do (note the code shown does not compile):

#include <stdio.h>
template <typename type>
type print(type *addr) 
{
  printf("type is: %s",type);
}

int main()
{
  int a;
  print(&a);
}

// Would like to print something like:
// type is: int

I think that the typename should be available at compile time when the function is instantiated, but I’m not that familiar with templates and I haven’t seen a way to get the typename as a string.

The reason that I want to do this is for some printf type debugging. I have multiple threads running and stepping through with gdb changes the program behavior. So for some things I want to dump information about which functions were executing. It’s not too important so if the solution is overly complex I would skip adding this information to my logging function. But if there was a simple way to do this it would be useful information to have.

Answer 1

__PRETTY_FUNCTION__ should solve your problem (at run time at least)

The output to the program below is:

asfdasdfasdf test<type>::test() [with type = int]
asfdasdfasdf test<type>::test() [with type = int]
asfdasdfasdf test<type>::test() [with type = int]
asfdasdfasdf test<type>::test() [with type = int]
asfdasdfasdf test<type>::test() [with type = int]
asfdasdfasdf test<type>::test() [with type = int]
asfdasdfasdf void tempFunction() [with type = bool]
asfdasdfasdf void tempFunction() [with type = bool]
asfdasdfasdf void tempFunction() [with type = bool]
asfdasdfasdf void tempFunction() [with type = bool]
asfdasdfasdf void tempFunction() [with type = bool]
asfdasdfasdf void tempFunction() [with type = bool]
!!!Hello World!!!

If you really, really, need the typename as a string, you could hack this (using snprintf instead of printf) and pull the substring after ‘=’ and before ‘]’.

#include <iostream>
using namespace std;

template<typename type>
class test
{
public:
test()
{
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
}
};

template<typename type>
void tempFunction()
{
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
    printf("asfdasdfasdf %s\n", __PRETTY_FUNCTION__);
}

int main() {
    test<int> test;

    tempFunction<bool>();
    cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
    return 0;
}