From `Learn C the Hard Way`

dbg.h

#ifndef __dbg_h__
#define __dbg_h__

#include <stdio.h>
#include <errno.h>
#include <string.h>

#ifdef NDEBUG
#define debug(M, ...)
#else
#define debug(M, ...) fprintf(stderr, "DEBUG %s:%d: " M "\n",\
        __FILE__, __LINE__, ##__VA_ARGS__)
#endif

#define clean_errno() (errno == 0 ? "None" : strerror(errno))

#define log_err(M, ...) fprintf(stderr,\
        "[ERROR] (%s:%d: errno: %s) " M "\n", __FILE__, __LINE__,\
        clean_errno(), ##__VA_ARGS__)

#define log_warn(M, ...) fprintf(stderr,\
        "[WARN] (%s:%d: errno: %s) " M "\n",\
        __FILE__, __LINE__, clean_errno(), ##__VA_ARGS__)

#define log_info(M, ...) fprintf(stderr, "[INFO] (%s:%d) " M "\n",\
        __FILE__, __LINE__, ##__VA_ARGS__)

#define check(A, M, ...) if(!(A)) {\
    log_err(M, ##__VA_ARGS__); errno=0; goto error; }

#define sentinel(M, ...)  { log_err(M, ##__VA_ARGS__);\
    errno=0; goto error; }

#define check_mem(A) check((A), "Out of memory.")

#define check_debug(A, M, ...) if(!(A)) { debug(M, ##__VA_ARGS__);\
    errno=0; goto error; }

#endif

test_dbg.c

#include "dbg.h"
#include <stdlib.h>
#include <stdio.h>

void test_debug()
{
    // notice you don't need the \n
    debug("I have Brown Hair.");

    // passing in arguments like printf
    debug("I am %d years old.", 37);
}

void test_log_err()
{
    log_err("I believe everything is broken.");
    log_err("There are %d problems in %s.", 0, "space");
}

void test_log_warn()
{
    log_warn("You can safely ignore this.");
    log_warn("Maybe consider looking at: %s.", "/etc/passwd");
}

void test_log_info()
{
    log_info("Well I did something mundane.");
    log_info("It happened %f times today.", 1.3f);
}

int test_check(char *file_name)
{
    FILE *input = NULL;
    char *block = NULL;

    block = malloc(100);
    check_mem(block);		// should work

    input = fopen(file_name, "r");
    check(input, "Failed to open %s.", file_name);

    free(block);
    fclose(input);
    return 0;

error:
    if (block) free(block);
    if (input) fclose(input);
    return -1;
}

int test_sentinel(int code)
{
    char *temp = malloc(100);
    check_mem(temp);

    switch (code) {
        case 1:
            log_info("It worked.");
            break;
        default:
            sentinel("I shouldn't run.");
    }

    free(temp);
    return 0;

error:
    if (temp)
        free(temp);
    return -1;
}

int test_check_mem()
{
    char *test = NULL;
    check_mem(test);

    free(test);
    return 1;

error:
    return -1;
}

int test_check_debug()
{
    int i = 0;
    check_debug(i != 0, "Oops, I was 0.");

    return 0;
error:
    return -1;
}

int main(int argc, char *argv[])
{
    check(argc == 2, "Need an argument.");

    test_debug();
    test_log_err();
    test_log_warn();
    test_log_info();

    check(test_check("ex20.c") == 0, "failed with ex20.c");
    check(test_check(argv[1]) == -1, "failed with argv");
    check(test_sentinel(1) == 0, "test_sentinel failed.");
    check(test_sentinel(100) == -1, "test_sentinel failed.");
    check(test_check_mem() == -1, "test_check_mem failed.");
    check(test_check_debug() == -1, "test_check_debug failed.");

    return 0;

error:
    return 1;
}

cc -Wall -g -DNDEBUG test_debug.c -o test_debug