Recompiling only if file changed

Code

Directory structure:

.
├── src
│   ├── utils.h
│   ├── utils.c
│   └── main.c
│
├── cbuild.h
└── cbuild.c

main.c - You app source code:

#include "stdio.h"
#include "utils.h"
int main(int argc, char** argv) {
    printf("Hello, world!\nSum: %d\n", sum(1, 1));
    return 0;
}

utils.h - Another source code file:

#ifndef UTILS_H
#define UTILS_H
int sum(int a, int b);
#endif // UTILS_H

utils.c - Another source code file:

#include "utils.h"
int sum(int a, int b) {
    return a + b;
}

cbuild.c - Your buildscript:

#include "cbuild.h"
int main(int argc, char** argv) {
    cbuild_selfrebuild(argc, argv);
    if (cbuild_compare_mtime("main.o", "src/main.c") > 0) {
        cbuild_cmd_t c1 = {0};
        cbuild_cmd_append_many(&c1, CC, "-c", "src/main.c");
        if (!cbuild_cmd_run(&c1)) {
            return 0;
        }
    }
    if (cbuild_compare_mtime("utils.o", "src/utils.c") > 0) {
        cbuild_cmd_t c2 = {0};
        cbuild_cmd_append_many(&c2, CC, "-c", "src/utils.c");
        if (!cbuild_cmd_run(&c2)) {
            return 0;
        }
    }
    cbuild_cmd_t l = {0};
    cbuild_cmd_append_many(&l, LD, "-o", "app.run", "utils.o", "main.o");
    if (!cbuild_cmd_run(&l)) {
        return 1;
    }
    return 0;
}

cbuild.h - Build system core.

How to run

cc -o cbuild.run cbuild.c
./cbuild.run
./app.run