template argument type to string

Question

I have code:

template<class T>
class MyClass{
    MyClass(){
       std::cout << MY_MACRO(T);
    }
};

Is it possible to write such macro that returns type of template argument as a string? If yes, how?

For example,

MyClass<int> ins; // print 'int' to console

Answer 1

As a couple other people have mentioned you could do something with RTTI but I don't think it is quite what you are looking for:

#include <typeinfo>
#include <iostream>
#include <string>

#define MY_MACRO(obj) typeid(obj).name()

template<class T>
class MyClass {
    public:
        MyClass(){
            T b;
            std::cout << MY_MACRO(b) << std::endl;
        }
};

class TestClass {};

int main(int argc, char** argv) {
    MyClass<std::string> a;
    MyClass<int> b;
    MyClass<TestClass> c;
    return 0;
}

Outputs:

Ss
i
9TestClass

Thanks to comment from @MM - if you are using gcc and don't mind making the macro into a function you could use abi::__cxa_demangle . You need to include cxxabi.h

size_t size;
int status;
std::cout << abi::__cxa_demangle(typeid(obj).name(), NULL, &size, &status) << std::endl;

Output:

std::string
int
TestClass

Answer 2

You could use overloaded functions for that like

std::string MY_MACRO(int) { return "int"; }

which is used as std::cout << MY_MACRO( T() ); , but you'll need to define such function for every type you use as template parameter.

Or you could use run-time type identification via typeid function.