Hi guys, why some compilers don't want to compile this:

main.cpp
#include "func.h"

int main()
{
    func();

    return 0;
}

func.h
void func()
{
    std::cout << "Hello\n";
}

It requires to include iostream to header file, but as i know at the preprocessing stage func.h together with the iostream will be inserted into the main.cpp and compiled as a translation unit.