Question

I have the following 3 files (1 *.cpp and 2 *.hpp) :

the main program file:

// test.cpp

#include<iostream>
#include"first_func.hpp"
#include"sec_func.hpp"

int main()
{
    double x;
    x = 2.3;
    std::cout << sec_func(x) << std::endl;
}

–
the first_func.hpp header:

// first_func.hpp

...

double  first_func(double x, y, x)
{

    return x + y + x;
}

–
the sec_func.hpp header:

// sec_func.hpp

...

double sec_func(double x)
{
        double a, b, c;
        a = 3.4;
        b = 3.3;
        c = 2.5;

        return first_func(a,b,c) + x;
}

How do I properly call first_func from within the sec_func.hpp file?

Answer 1

It’s a bad practice to place function definition to .hpp files. You should place only function prototypes there. Like this:

first_func.hpp:

double  first_func(double x, double y, double x);

first_func.cpp:

double  first_func(double x, double y, double x)
{
    return x + y + x;
}

The same for second func.

And then, wherever you want to call your first_func, you just include corresponding first_func.hpp in that cpp module, and write the call.

Thus, every your module consists of hpp with all declarations, and cpp with definitions (that is, the bodies). When you need to reference something from this module, you include its hpp and use the name (of constant, variable, function, whatever).

And then you must link everything together:

gcc main.cpp first_func.cpp second_func.cpp -o program