How do I make my header, function and main file work together, I always get: error: Id returned 1 ex-CodePudding

I made a very simple C program where the goal is to use functions in different files. The function justs prints out a certain message passed in a parameter. After some research, I read that for such project, I need 3 files: the main, the header and the function (apparently I shouldn't put the function code in the header file.) I now have three files:

main.cpp (main file)
simple.h (header file (function definition))
simple.cpp (function file)

Whenever I try to make them work together, I always get the same error:

    C:\Users\juuhu\AppData\Local\Temp\ccQRa0R0.o:main.cpp:(.text 0x43): undefined reference to `message(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
collect2.exe: error: ld returned 1 exit status

Here's the code of the three files:

main.cpp

#include <iostream>
#include "simple.h"

using namespace std;

int main(){
    message("Hello world!");
    return 0;
}

simple.h

#ifndef SIMPLE_H_INCLUDED
#define SIMPLE_H_INCLUDED

#include <string>

void message(std::string message);

#endif

simple.cpp

#include "simple.h"

void message(std::string message){
    cout << message;
}

CodePudding user response：

I was use visual studio 2019 to compile your code. First compile error output:"Error C2065 'cout': undeclared identifier message".

When I add #include<iostream> in simple.h and change simple.cpp message function the cout to std::cout, the program output "Hello world!"

simple.h

#ifndef SIMPLE_H_INCLUDED
#define SIMPLE_H_INCLUDED
#include<iostream>
#include <string>

void message(std::string message);

#endif

simple.cpp

#include "simple.h"

void message(std::string message) {
    std::cout << message;
}

you can try again, hope you are successful to compile the code and get your to want.

CodePudding user response：

You haven't link the function defination file to the header file.

simple.h

#ifndef SIMPLE_H_INCLUDED
#define SIMPLE_H_INCLUDED

#include <string>
#include "simple.cpp" // include the simple.cpp file

void message(std::string message);

#endif