How to Integrate the Minimalist C Logging Library log.c into Your Projects

Overview

log.c is a minimal C logging library (single .c and .h, under 200 lines) that provides multiple log levels, file output, and optional thread‑safety.

Repository

git clone https://github.com/akstuki/log.c.git

Internal State

static struct {
    void *udata;          /* user data for lock callback */
    log_LockFn lock;      /* custom lock function */
    FILE *fp;             /* file handle for log output */
    int level;            /* current log level */
    int quiet;            /* non‑zero suppresses console output */
} L;

Configuration macros

LOG_USE_COLOR – enable ANSI colour codes in terminal output.

API Functions

log_set_fp(FILE *fp)

– set output file. log_set_lock(log_LockFn fn) – register lock callback. log_set_udata(void *udata) – set user data passed to lock. log_set_quiet(int enable) – 0 = console output, 1 = silent. log_set_level(int level) – change active log level (e.g., LOG_TRACE, LOG_ERROR).

Example

main.c demonstrates initializing a pthread mutex as the lock, opening a log file, and emitting logs at different levels.

/* main.c */
#include <stdio.h>
#include <pthread.h>
#include "log.h"

#define LOG_FILE_NAME "peng.log"

pthread_mutex_t log_mutex;

void log_mutex_fn(void *udata, int lock) {
    if (lock) pthread_mutex_lock(&log_mutex);
    else       pthread_mutex_unlock(&log_mutex);
}

void my_log_lock_init(const char *info) {
    pthread_mutex_init(&log_mutex, NULL);
    log_set_lock(&log_mutex_fn);
    log_set_udata((void *)info);
}

void my_fp_init(const char *filename) {
    FILE *fp = fopen(filename, "w+");
    if (!fp) {
        printf("%s open fail
", filename);
        return;
    }
    log_set_fp(fp);
}

int main(void) {
    my_log_lock_init("peng");
    my_fp_init(LOG_FILE_NAME);
    log_set_quiet(0);
    printf("Setting log level to LOG_TRACE.
");
    log_set_level(LOG_TRACE);
    log_trace("Sample log message.");
    log_debug("Sample log message.");
    log_info ("Sample log message.");
    log_warn ("Sample log message.");
    log_error("Sample log message.");
    log_fatal("Sample log message.");

    printf("Setting log level to LOG_ERROR.
");
    log_set_level(LOG_ERROR);
    log_trace("Sample log message.");   /* ignored */
    log_debug("Sample log message.");   /* ignored */
    log_info ("Sample log message.");  /* ignored */
    log_warn ("Sample log message.");  /* ignored */
    log_error("Sample log message.");
    log_fatal("Sample log message.");
    return 0;
}

Compilation

gcc main.c log.c -o run

Running

Executing ./run prints coloured logs to the terminal and writes the same entries to peng.log. Adjust log_set_level and log_set_quiet to control verbosity and output destination.