Question

I’m confused about friend operator overloading. It has no problem if I write the friend operator overloading function within the header file, but it gives me the following errors once I moved the function to class file. I googled some samples and they all written the function in the header file. What did I do wrong? Thanks.

...: error: expected ‘,’ or ‘...’ before ‘&’ token
...: error: ISO C++ forbids declaration of ‘statisticain’ with no type
...: error: ‘main_savitch_2C::statistician operator+(int)’ must have an argument of class or enumerated type


// a.h
class A
{
    public:
        friend A operator + (const A &a1, const A &a2);
};

// a.cpp
#include "a.h"
A operator + (const A &a1, const A &a2)
{
    //
}

Answer 1

From the error message you’re getting:

ISO C++ forbids declaration of ‘statisticain’ with no type

I think that you misspelled “statistician” by reversing the last two letters (note that you have “statisticain” instead of “statistician.”)

This should have nothing to do with whether operator+ is implemented in the header or the .cpp file.