Question

I am heaving a weird issue with inlining functions defined in different files. Consider the following scenario.

in main.c:

#include "inline.h"
int main(void) {
    int i = 0;
    for (i = 0; i<=100000; i++) {
        omfg(i);
    }
    return 0;
 }

in inline.h:

inline int omfg(unsigned int num);

and in inline.c:

#include <stdio.h>
inline int omfg(unsigned int num) {
    int i = 0;
    for (i = 0; i<= 10; i++) {
        printf(".");
        num++;
    }
    return num;
 }

When I compile with gcc using something similar to:

$ gcc inline.c main.c -o binary -Wall -Winline -Wextra -O2

I get:

main.c: In function 'main':
inline.h:2: warning: inlining failed in call to 'omfg': function body not available
main.c:7: warning: called from here

What am I doing wrong? Should I declare omfg() in a different way? Its quite puzzling…

Answer 1

Move the implementation to the header file. You can declare the function up front then define it below, or even #include a special file like inline.inl at the bottom of the header to hide it, but fundamentally the function definition needs to be available if it’s to be inline.