Sharing a function in a folder in C++ - c++

Question

Sorry for this question, which is probably a pretty nooby question, but i just don't know how to get my problem solved.
I have a function that returns true or false, rather the one number is a divider of an other number or not.
Now i need this function in two of my programs and instead of just copy-pasting it, i want to write this function in its own file and then include it in the programs.
What is the best way to do that?
I don't use VisualStudio, so I think I can't create a library.

Answer 1

You can create a header-only "library". That is, a single header file, say "my.h", which contains the definition of your function:
#ifndef MY_LIBRARY_UNIQUE_ID_OR_SOMETHING //these are called include guards,
#define MY_LIBRARY_UNIQUE_ID_OR_SOMETHING //look them up
inline bool myFunc()
{
return true;
}
#endif
Do note that the function must be inline. Otherwise you may get "function redefinition" linker errors.
In order to use this "library", all you have to do is #include "my.h" (with correct path, of course). Hope this helps

Answer 2

Create a file with an extension .h. For example: myheader.h
Then write to myheader.h the following:
#ifndef MYHEADER_H
#define MYHEADER_H
bool is_divider(int, int);
#endif
Write a source file named myheader.cpp
Inside the myheader.cpp write:
#include"myheader.h"
bool is_divider(int a, int b) {
/your code here
}
include the header myheader.h to the files you need to use is_divider()
Note that if you are using an IDE you should do the following:
Add the .cpp and .h files to your project
Include the path of the headers on the IDE options.
For example, if you are using codeblocks you can see the process here (keep in mind that same procedure applies in other IDE's as well)
If you are using a terminal and an editor you can create a makefile. A nice tutorial can be found here

Answer 3

Use a header file to share the function between both programs. The header file extension can take different forms. The most common extension is .h however there are others such as .hpp.
For example, a header file named foo.h might contain:
#pragma once // include this file just once
inline bool foo()
{
return false;
}
To use the header file you would include it from the .cpp file as follows:
#include "foo.h" // when foo.h is located in the same directory as the .cpp file
#include <foo.h> // when foo.h is located in a project additional include folder
#include "../foo.h" //when foo.h is located up one directory from the .cpp file

Answer 4

You need to create a header file with the function. Here are 3 options:
Option 1
Define function in header file
Here is an example:
Create a file header.h
Give it the following code:
#pragma once
inline int random()
{
return 4; //Strictly random
}
If your compiler doesn't support #pragma, use header guards, like this:
#ifndef HEADER_H_OR_ID
#define HEADER_ H_OR_ID
inline int random()
{
return 4; //Strictly random
}
#endif
For this option, every file that wants to use the function has to include "header.h"
Option 2
Forward declare the function in a header file, and implement in every source file
Example:
#ifndef HEADER_H_OR_ID
#define HEADER_H_OR_ID
int random();
#endif
Source.cpp
#include "header.h"
int random() {return 4;}
But unfortunately, this is not probably not what you want, although it allows uniqueness per file.
Option 3
Forward declare the function in a header file, and implement in corresponding source file
Example:
Header.h
#ifndef HEADER_H
#define HEADER_H
int random();
#endif
Header.cpp
#include "Header.h"
int random() {return 4;}
Here, you have to include the source file with the main file, such as by linking them on the command line like this:
g++ main.cpp header.cpp
Tools like Visual Studio already would link all files, so nothing manual, other than creating files, is necessary.