How do I share a global variable between c files?

If I define a global variable开发者_运维知识库 in a .c file, how can I use the same variable in another .c file?

file1.c:

#include<stdio.h>

int i=10;

int main()
{
    printf("%d",i);
    return 0;
}

file2.c:

#include<stdio.h>

int main()
{
    //some data regarding i
    printf("%d",i);
    return 0;
}

How can the second file file2.c use the value of i from the first file file1.c?

file 1:

int x = 50;

file 2:

extern int x;

printf("%d", x);

Use the extern keyword to declare the variable in the other .c file. E.g.:

extern int counter;

means that the actual storage is located in another file. It can be used for both variables and function prototypes.

using extern <variable type> <variable name> in a header or another C file.

In the second .c file use extern keyword with the same variable name.

Do same as you did in file1.c In file2.c:

#include <stdio.h> 

extern int i;  /*This declare that i is an int variable which is defined in some other file*/

int main(void)
{
/* your code*/

If you use int i; in file2.c under main() then i will be treated as local auto variable not the same as defined in file1.c

Use extern keyword in another .c file.

If you want to use global variable i of file1.c in file2.c, then below are the points to remember:

1. main function shouldn't be there in file2.c
2. now global variable i can be shared with file2.c by two ways:
   a) by declaring with extern keyword in file2.c i.e extern int i;
   b) by defining the variable i in a header file and including that header file in file2.c.