Accessing a variable outside a c file-CodePudding

I'm trying to do this code, and I split it up into .c files (lets say file1.c and file2.c) and file1.h file. I'm not allowed to change which parameters I can send to the function, so I need to find another way to "send"/access another variable. I tried to make the variable static in the header file file1.h, and include it in the file2.c. The function in file1.c look something like this:

int function(int *array, int a, int b){
        ...
        ...
    if(global_variable == 1){
        point = array[(a b)/2];
    }else if(global_variable == 0){
        point = array[b];
    }

and in the file2.c I have a function something like this:

double function2(t_sort_funcp fun, const case_t c, int array_length, result_t *buf, t_generate_array_funcp g_array){
    int array[array_length];
    switch (c)
    {
    case first:
        global_variable = 1;
        g_array(array, array_length);
        return debugg(fun, array, array_length);
        break;
    case second:// Wors case is an inverted sorted array.
        global_variable = 0;
        g_array(array, array_length);
        return debugg(fun, array, array_length);
        break;
    case third:
        global_variable = 1;
        g_array(array, array_length);
        return debugg(fun, array, array_length);
        break;
    }
    return 0;
}

In the file1.h I have:

#ifndef ALGORITHM_H
#define ALGORITHM_H

#include <stdbool.h> // bool
static int global_variable;

#endif

as you can see, I'm trying to change the global_variable variable in file2.c and use it in file1.c but that does not work, the if-statement in file1.c always executes the code in the else-statement, even if I changed the variable to 1. NOTE: file2.c always executes before file1.c

CodePudding user response：

Do it the opposite way

#ifndef ALGORITHM_H
#define ALGORITHM_H

#include <stdbool.h> // bool
extern int global_variable;

#endif

In one of the .c files

int global_variable;

Include the .h file in all files which require access to this variable.

static in global scope makes the variable only available in one compilation unit (file).

CodePudding user response：

You can use extern with a cpp conditional.

Below are samples files.

FILE: file1.h

#ifndef ALGORITHM_H
#define ALGORITHM_H

#include <stdbool.h> // bool

#ifdef FILE1_C
int global_variable;
#else
extern int global_variable;
#endif

#endif

FILE: file1.c

// I am file1.c
#define FILE1_C
#include "file1.h"

FILE: file2.c

// I am file2.c
#include "file1.h"

UPDATE:

definitely wrong way. Why this weird ifdef complication – 0___________

No, it's not the wrong way. I do this all the time. The idea is that you have both definitions in the same place/file. If you put the global in a .c file, it's harder to see if you change the type.

Here's a more expanded case:

#ifndef ALGORITHM_H
#define ALGORITHM_H

#include <stdbool.h> // bool

#ifdef FILE1_C
#define EXTRN_FILE1     /**/
#else
#define EXTRN_FILE1     extern
#endif

EXTRN_FILE1 int global_variable;
EXTRN_FILE1 double global_variable_2;

#ifdef FILE1_C
int global_variable_3 = 37;
#else
extern int global_variable_3;
#endif

#endif

And, we may want to put the globals in a different .c file. If we rename FILE1_C to (e.g.) DEFINE_GLOBALS, we can put #define DEFINE_GLOBALS in any .c. If we change our minds later, it's trivial to move the #define from (e.g.) file1.c to file2.c.