resource_path.c

#include <libgen.h>
#include <linux/limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static const char MARKER_FILE[] = "build.ninja";

static bool exe_in_build_dir(void)
{
    char exe_path[PATH_MAX + 1];
    ssize_t n = readlink("/proc/self/exe", exe_path, PATH_MAX);
    if (n == -1) {
        return false;
    }
    exe_path[n] = '\0';

    char path[PATH_MAX + sizeof(MARKER_FILE) + 1];
    snprintf(path, sizeof(path), "%s/%s", dirname(exe_path), MARKER_FILE);

    return access(path, F_OK) == 0;
}

const char* resource_path(void)
{
    if (exe_in_build_dir()) {
        return "@BUILD_DIR@";
    } else {
        return "@INSTALL_DIR@";
    }
}

resource_path.h

#ifndef RESOURCE_PATH_H
#define RESOURCE_PATH_H

const char* resource_path(void);

#endif