A simple logging library implemented in C99

log.c and log.h should be dropped into an existing project and compiled along with it. The library provides 6 function-like macros for logging:

#include "log.h"

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>


static pthread_mutex_t     mutex_log;

static void log_lock(bool lock, void *udata)
{
	pthread_mutex_t *mtx = (pthread_mutex_t *)udata;
	if(lock)
    {
        int ret = pthread_mutex_lock(mtx);
        if(ret == EOWNERDEAD)
        {
            if(pthread_mutex_consistent(mtx))
            {
                perror("pthread_mutex_consistent failed:");
            }
        }
    }
    else 
    {
        pthread_mutex_unlock(mtx);       
    }
}

int main(void)
{
    log_open();
    
    pthread_mutexattr_t attr;

    pthread_mutexattr_init(&attr);
    pthread_mutexattr_setrobust(&attr, PTHREAD_MUTEX_ROBUST);

	if(pthread_mutex_init(&mutex_log, &attr) != 0)
    {
        log_fatal("mutex init error!\n");
    }

    log_set_lock(log_lock, &mutex_log);

    log_set_quiet(false);
    log_set_level(LOG_TRACE);
    log_set_file_limit(512);

    log_add_fp("./log_out", LOG_TRACE);

	log_trace("This is a log");
	log_debug("This is a log");
	log_info("This is a log");
	log_warn("This is a log");
	log_error("This is a log");
	log_fatal("This is a log");

	log_close();

	return 0;
}

Each function takes a printf format string followed by additional arguments:

log_trace("Hello %s", "world")

Resulting in a line with the given format printed to stderr:

20:18:26 TRACE src/main.c:11: Hello world

log_open() should be used first. Then you can use log_xxx function.

log_close() should be used when you exit process.

Quiet-mode can be enabled by passing true to the log_set_quiet() function. While this mode is enabled the library will not output anything to stderr, but will continue to write to files if any are set.

The current logging level can be set by using the log_set_level() function. All logs below the given level will not be written to stderr. By default the level is LOG_TRACE, such that nothing is ignored.

One or more file paths where the log will be written can be provided to the library by using the log_add_fp() function. The data written to the file output is of the following format:

2047-03-11 20:18:26 TRACE src/main.c:11: Hello world

Any messages below the given level are ignored. If the library failed to add a file path a value less-than-zero is returned.

If the log will be written to from multiple threads a lock function can be set. The function is passed the boolean true if the lock should be acquired or false if the lock should be released and the given udata value.

Set the limit of log file size.

The default value is 0,which means there isn't limit for log file.

If the log string is larger than limit,the log string will be written rollback at the beginning of file.

If the library is compiled with -DLOG_USE_COLOR ANSI color escape codes will be used when printing.

This library is free software; you can redistribute it and/or modify it under the terms of the MIT license. See LICENSE for details.