Function return type validation by compiler

Question

I read in Thinking in C++ by Bruce Eckel that when a C++ compiler encounters a function it decorates it's name using it's name and arguments. For a function, int func(char ch); it would decorate it's name as _func_char It doesn't use the return type.

In that case, In the below program how does the compiler complain "invalid conversion from int to const char*" when it has not stored the return type during function name decoration? Can anyone please clarify?

#include <iostream>

using namespace std;

int func()
{
    int i = 5;
    return i;
}

int main()
{
    string str = func();
}

Answer 1

Symbol (not just functions) name mangling comes into play at the linking stage. You're getting a compiler error.

The compiler doesn't see the mangled name. It just sees you have a function called func that returns an int and takes no parameters, and so can tell you your code is illegal.

Answer 2

This is an compilation error.
Compiler checks for the validity of the C++ program as per the C++ Standard specification.

Why does the compiler report an error here?

Because compiler can see that return type of the function is int and it is being used to initialize a variable of the type std::string and there is no valid implicit conversion for it.

Note that the language is designed in such a way it allows the compiler to do these kind of type checking, C++ is a statically typed language .