I want to run a small simulation in c .
To keep everything nice and readable I seperate each thing (like all the sdl stuff, all the main sim stuff, ...) into it's own .h file.
I have some variables that I want all files to know, but when I #include them in more then one file other the g compliler sees it as a redefinition.
I understand why he does this, but this still leaves me with my wish to have one file where all important variables and constants for each run are defined and known to all other files, to easily find and change them when running my simulation.
So my Question here: Is there a good workaround to achieve that or something similar?

CodePudding user response：

You can put the declarations for all the globals in a header and then define them in a source file and then you will be able to use those global variables in any other source file by just including the header as shown below:

header.h

#ifndef MYHEADER_H
#define MYHEADER_H


//declaration for all the global variables 
extern int i; 
extern double p;


#endif 

source.cpp

#include "header.h"
//definitions for all the globals declared inside header.h
int i = 0;
double p = 34;

main.cpp

#include <iostream>
#include "header.h" //include the header to use globals 
int main()
{
    std::cout << i <<std::endl;//prints 0
    std::cout<< p << std::endl;//prints 34
    return 0;
}

Working demo

CodePudding user response：

Mark them as extern in the header and have one translation unit that defines them.

Note: Without LTO (link time optimization) this will seriously slow down your simulation.