log.c

A simple logging library implemented in C99

Usage

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:

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_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

log_set_quiet(bool enable)

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 and callbacks if any are set.

log_set_level(int level)

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.

log_add_fp(FILE *fp, int level)

One or more file pointers 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 pointer a value less-than-zero is returned.

log_add_callback(log_LogFn fn, void *udata, int level)

One or more callback functions which are called with the log data can be provided to the library by using the log_add_callback() function. A callback function is passed a log_Event structure containing the line number, filename, fmt string, va printf va_list, level and the given udata.

log_set_lock(log_LockFn fn, void *udata)

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.

const char* log_level_string(int level)

Returns the name of the given log level as a string.

LOG_USE_COLOR

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

LOG_LOC_ALIGN

If the library is compiled with -DLOG_LOC_ALIGN, the width of the log line reserved for the location of in the file (e.g. src/main.c:238) will be constant, either padded or truncated depending on the size of the file.

The actual width is defined with the macro LOG_LOC_LEN and defaults to 16. If needed, this width can be overriden to n by giving the -DLOG_LOC_LEN=n flag to the compiler.

LOG_PID

If the library is compiled with -DLOG_PID, each log line will be show the PID of the calling process. You might not use this if your program is performance- critical and particularly verbose, as each log line will call the getpid(2) syscall.

License

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