Logging library for C

Question

I am looking for a productive and simple logging library for C, which can output the log to a file. Displaying messages in the log I want to make like this:

date-time tag message

It would be nice to control the level of detail of messages and control the size of the file.

I found two projects that are suitable for me. It log4c and nglogc.

log4c seemed too big. nglogc quite fit, but also has a redundant functional. maybe you tell me more variants?

Answer 1

You can use this

File logger.h

#ifndef LOGGER_H
#define LOGGER_H

void logger(const char* tag, const char* message);

#endif /* LOG_H */

File logger.c

#include "logger.h"
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void logger(const char* tag, const char* message) {
   time_t now;
   time(&now);
   printf("%s [%s]: %s\n", ctime(&now), tag, message);
}

It's probably not perfect, but it does satisfy the needs as you have presented them.

Answer 2

I suggest the log library which is written by myself --- zlog!

The way to fit your need in zlog is:

$ vi /etc/zlog.conf
[formats]
simple = "%D %c %m%n"
# don't know what the tag mean in your question, so put category of zlog instead
# log level is also available here, add %V means level

[rules]
my_cat.*   "xxx.log"; simple

$ vi hello.c
#include <stdio.h> 
#include "zlog.h"

int main(int argc, char** argv)
{
int rc;
zlog_category_t *c;

rc = dzlog_init("/etc/zlog.conf", "my_cat");
if (rc) {
    printf("init failed\n");
    return -1;
}

zlog_info(c, "hello, zlog");

zlog_fini();

return 0;
} 

It will generate xxx.log in current directory as

2012-09-30 07:22:50 my_cat hello, zlog

Links:

Download: https://github.com/HardySimpson/zlog/archive/latest-stable.tar.gz

UsersGuide: http://hardysimpson.github.com/zlog/UsersGuide-EN.html

Hompage: http://hardysimpson.github.com/zlog/

Answer 3

Here is mine:

log.h
------

#ifndef LOG_H 
#define LOG_H


void log_error(const char* message, ...); void log_info(const char* message, ...); void log_debug(const char* message, ...);

#endif

log.c
------
#include "log.h"


void log_format(const char* tag, const char* message, va_list args) {   time_t now;     time(&now);     char * date =ctime(&now);   date[strlen(date) - 1] = '\0';  printf("%s [%s] ", date, tag);  vprintf(message, args);     printf("\n"); }

void log_error(const char* message, ...) {  va_list args;   va_start(args, message);    log_format("error", message, args);     va_end(args); }

void log_info(const char* message, ...) {   va_list args;   va_start(args, message);    log_format("info", message, args);  va_end(args); }

void log_debug(const char* message, ...) {  va_list args;   va_start(args, message);    log_format("debug", message, args);     va_end(args); }

Have fun!

Answer 4

You can use this simple logging library: https://github.com/kala13x/slog

Here is an example how to use:

At first you must init log. with init_log() function. First argument is log filename, second argument is log to file (1 enabled, 0 disabled) and third argument is max log level

init_slog("example", 1, 3);

print and log something

slog(0, "Test message with level 0");
slog(2, "Test message with level 2");
slog(0, "Test message with int argument: %d", int_arg);

Outout will be something like that:

2015:04:02:56 - Test message with level 0
2015:04:02:56 - Test message with level 2
2015:04:02:56 - Test message with int argument: 69

Answer 5

Take a look at the zf_log logging library. It's small, simple and provides essentials only. From README.md:

This is just a thin wrapper around sprintf() function. It provides less than 20% of functionality found in more sophisticated libraries, but covers more than 80% of common use cases. Focus is made on simplicity, ease of use and performance (to be more precise - low overhead).

Features:

• Debug logging is reduced to no-op in release builds
• Arguments are not evaluated when the message is not logged
• No "unused" warning for variables used in log statements only
• Log a memory region as HEX and ASCII
• Custom output functions

Answer 6

I am also finding solutions on this problem. The answer from @edwin-buck is just simple and OK for my need.

I really know nothing on multi-threading and thread-safe, but after compiling under Visual Studio compiler (it can give some warnings and tips), and searching through google, I think a few modification might make the code above thread-safe and better.

// file log.c
void log(const char* tag, const char* message) {
   time_t now;
   struct tm _calendar_time;
   char _buf[MAX_COUNT];

   time(&now);
   localtime_s(&_calendar_time, &now);

   strftime(_buf, MAX_COUNT, "%c", &_calendar_time);
   printf("%s [%s]: %s\n", _buf, tag, message);
}

Feel free to correct me if wrong.