Thread: How to get the type of a variable without the "typeinfo" header?

I don't want to link the C++ (not even C's libc) and I want to learn how (and if) I can get the type of a variable for a comparison. For example I want to do something like the following:

Code:

#include <stdio.h> 

template <typename T>
void print_type(T num) {   
  if constexpr(typeof(num) == typeof(double)) {
    printf("It is a double!");   
  } else if constexpr(typeof(num) == typeof(double)) {     
    printf("It is an integer!");   }
}

Is there any way to do that without using the C++ "typeinfo" header?

Originally Posted by john.c

typeof is a gcc extension. typeid is part of C++, but you must include <type_info>. decltype doesn't need <type_info>. It can be used like this (maybe there's an easier way, but this works).

Code:

#include <iostream>
 
template<class T, class U> struct is_same {
    static constexpr bool value = false;
};
 
template<class T> struct is_same<T, T> {
    static constexpr bool value = true;
};
 
int main()
{
    using std::cout;
    double a;
    int b;
 
    if (is_same<decltype(a), int   >::value) cout << "a is int\n";
    if (is_same<decltype(a), double>::value) cout << "a is double\n";
    if (is_same<decltype(b), int   >::value) cout << "b is int\n";
    if (is_same<decltype(b), double>::value) cout << "b is double\n";
}

Thanks a lot!!!! It works as expected!!! Now I'll probably use C++ over D

Originally Posted by Salem

Also here -> How to get the type of a variable withou - C++ Forum

Yeah, that's from me. I decided to post in both these forums to get more chances to get answers. But it seems nobody other than you answer here while we already have one more answer here which also solves my problem. I think I'll give the other forum a try for my next question in it will be decided if I'm going to posting only here after that.

In case someone is interested. The <type_traits> header has a std::is_same type already.
std::is_same - cppreference.com

Originally Posted by thmm

In case someone is interested. The <type_traits> header has a std::is_same type already.
std::is_same - cppreference.com

Thanks! Do you know how is this implemented? I wonder if this is going to be faster to compile and lighter on runtime than the answer given by john.c.

I guess each compiler might implement it differently. If it is faster only a benchmark can tell.
To test it easily and quickly, have a look at Quick C++ Benchmarks