CODEWITHSUNDEEP
cfunctionsyntaxheader-files
phantomBlurrr
phantomBlurrr

Reputation: 295

How to use a function from a second C file in the main C file?

I'm trying to split up a large C file because it's very difficult to read and keep track of what's doing what. I read up on it and it supposed to be as simple as creating a c file that contains the function, then a header file that references the function, then include the header file in main c file and simply use the function. However, I've done that and the function in question isn't actually being called in my code.

I tried placing printf statements in the function so I could see if it was really being called and these do not show up in monitor (which I interpret as the function is not being called)

//MAIN.c
#include "just_printf.h"

void app_main(){
    printf("attempting to call print\n");
    just_print();
}

//---------------------------------------
//JUST_PRINTF.h
#ifndef MAIN_JUST_PRINT_H_
#define MAIN_JUST_PRINT_H_

void just_print();

#endif

//---------------------------------------
//JUST_PRINTF.c
#include "just_printf.h"

void just_print(){
    printf("tried to prrint");
}

When I run main.c, it's supposed to print "attempting to call print" then when it calls just_print() it's supposed to print "tried to prrint". This is just a sanity check before I try moving actual functionality out of my main.c file. What am I doing wrong? Am I misunderstanding how to split up a c file? Right now all I get is the first printf statement before the function call.

Upvotes: 2

Views: 317

Answers (1)

gsamaras
gsamaras

Reputation: 73444

In main.c, change:

void app_main() {

to:

int main(void) {

and then compile like:

gcc main.c just_printf.c

and the output will be (after executing a.out):

Georgioss-MBP:~ gsamaras$ ./a.out 
attempting to call print
tried to prrint

You should get a warning about implicit declaration of the function printf, since you don't include stdio.h - do that in the header file, I would suggest, like this: 

#include <stdio.h>

Suggestion: In the header file, the include guard would be usually written like:

JUST_PRINT_H

i.e., without the trailing underscore, and the full name of the file, in capital characters.

Upvotes: 2

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