A simple logging library implemented in C99

log.c and log.h should be dropped into an existing project and compiled along with it. This project can also be included as a git submodule. The library provides 7 function-like macros for logging:

log_trace(const char *fmt, ...);
log_debug(const char *fmt, ...);
log_info(const char *fmt, ...);
log_warn(const char *fmt, ...);
log_error(const char *fmt, ...);
log_perror(const char *fmt, ...);
log_fatal(const char *fmt, ...);

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

Quiet-mode can be enabled by passing 1 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 the file if one is set.

The current logging level can be set by using the log_set_level() function. All logs below the given level will be ignored. By default the level is LOG_TRACE, such that nothing is ignored.

A file pointer where the log should be written can be provided to the library by using the log_set_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

The current logging level for file output can be set by using the log_set_file_level() function. All logs below the given level will be ignored. By default the level is LOG_TRACE, such that nothing is ignored. The main log level supersedes the file log level, so if the file log level is lower than the main log level, only logs at or above the main log level will be written to file.

If the log will be written to from multiple threads a lock function can be set. The function is passed a udata value (set by log_set_udata()) and the integer 1 if the lock should be acquired or 0 if the lock should be released.

This function has the same precedence as log_error but also prints error information from the glibc errno variable (just like the perror function).

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

If NODEBUG or RELEASE are defined, then all calls to log_trace and log_debug will be no-operations. This is important for tight loops. This can be set at import time.

The following have the same functionality as the longer log_**** calls:

#define LOGT log_trace
#define LOGD log_debug
#define LOGI log_info
#define LOGW log_warn
#define LOGE log_error
#define LOGP log_perror
#define LOGF log_fatal

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