Logging library for C applications
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README.md

Yder

Logging library written in C.

Simple and easy to use logging library. You can log messages to the console, a file, syslog or journald.

Yder is mono-thread, which mean that you can use only one instance of yder log at the same time in your program.

Installation

Distribution packages

Packaging status

Yder is available in multiple distributions as official package. Check out your distribution documentation to install the package automatically.

$ # Example for Debian testing
$ sudo apt install libyder-dev # Or apt install libyder2.0 if you don't need the development files

Pre-compiled packages

You can install Yder with a pre-compiled package available in the release pages. Note that you need to install Orcania first. jansson development files packages is required to install Yder.

Manual install

Prerequisites

You must install liborcania first before building libyder. Orcania will be automatically installed if missing and you're using cmake.

CMake - Multi architecture

CMake minimum 3.5 is required.

Run the cmake script in a subdirectory, example:

$ git clone https://github.com/babelouest/yder.git
$ cd yder/
$ mkdir build
$ cd build
$ cmake ..
$ make && sudo make install

The available options for cmake are:

  • -DWITH_JOURNALD=[on|off] (default on): Build with journald (SystemD) support
  • -DBUILD_STATIC=[on|off] (default off): Build the static archive in addition to the shared library
  • -DBUILD_TESTING=[on|off] (default off): Build unit tests
  • -DINSTALL_HEADER=[on|off] (default on): Install header file yder.h
  • -DCMAKE_BUILD_TYPE=[Debug|Release] (default Release): Compile with debugging symbols or not

Good ol' Makefile

Download yder from github repository, compile and install.

$ git clone https://github.com/babelouest/yder.git
$ cd yder/src
$ make
$ sudo make install

To build Yder without Journald (SystemD) support, add the option Y_DISABLE_JOURNALD=1 to the make command:

$ git clone https://github.com/babelouest/yder.git
$ cd yder/src
$ make Y_DISABLE_JOURNALD=1
$ sudo make install

By default, the shared library and the header file will be installed in the /usr/local location. To change this setting, you can modify the DESTDIR value in the src/Makefile.

Example: install yder in /tmp/lib directory

$ cd src
$ make && make DESTDIR=/tmp install

You can install Yder without root permission if your user has write access to $(DESTDIR). A ldconfig command is executed at the end of the install, it will probably fail if you don't have root permission, but this is harmless. If you choose to install Yder in another directory, you must set your environment variable LD_LIBRARY_PATH properly.

Install libyder as a static archive

Install byderlibrary as a static archive, libyder.a, use the make commands make static*:

$ cd src
$ make static && sudo make static-install # or make DESTDIR=/tmp static-install if you want to install in `/tmp/lib`

API Documentation

Header files and compilation

To use yder in your code, you must include the file yder.h.

#include <yder.h>

Initialization

Use the y_init_logs function to start logging. The prototype of this function is:

/**
 * Initialize logging with mode and level parameters, specify a log file if needed
 * Return true on success, false on error
 */
int y_init_logs(const char * app, const unsigned long init_mode, const unsigned long init_level, const char * init_log_file, const char * message);

The parameter init_mode is the initial mode for logging. You can specify and combine the following modes available:

Y_LOG_MODE_CONSOLE
Y_LOG_MODE_SYSLOG
Y_LOG_MODE_JOURNALD
Y_LOG_MODE_FILE
Y_LOG_MODE_CALLBACK

If you use Y_LOG_MODE_FILE in your initial mode, you must specify a valid path for the init_log_file parameter.

The parameter init_level is the bottom level of your log messages. The levels available are, by level order:

Y_LOG_LEVEL_NONE
Y_LOG_LEVEL_ERROR
Y_LOG_LEVEL_WARNING
Y_LOG_LEVEL_INFO
Y_LOG_LEVEL_DEBUG

For example, if you specify Y_LOG_LEVEL_WARNING as init_level, you will see in your log output only Y_LOG_LEVEL_WARNING and Y_LOG_LEVEL_ERROR. If you specify Y_LOG_LEVEL_DEBUG, you will see in your log output all log messages.

Redirect log messages to a callback function

If you need to redirect log messages to a custom callback function, for example if you need to interact with other logging libraries, you must use the init_mode Y_LOG_MODE_CALLBACK in the init_mode parameter in the y_init_logs function, then use the function y_set_logs_callback with your callback function as parameter.

/**
 * Specify a callback function that will catch all log messages
 * In addition to other logs output already defined in y_init_logs
 */
int y_set_logs_callback(void (* y_callback_log_message) (void * cls, const char * app_name, const time_t date, const unsigned long level, const char * message),
                        void * cls,
                        const char * message);

The callback log function must have the following signature:

void y_callback_log_message(void * cls, const char * app_name, const time_t date, const unsigned long level, const char * message);

The parameters in the callback function are:

- void * cls // Your specified parameter
- const char * app_name // The value app_name from y_init_logs
- const time_t date // The datestamp when the log message was launched
- const unsigned long level // The log level of the message, values can be: Y_LOG_LEVEL_ERROR, Y_LOG_LEVEL_WARNING, Y_LOG_LEVEL_INFO, Y_LOG_LEVEL_DEBUG

Close yder

To close yder and free its allocated memory, use the function y_close_logs:

/**
 * Close the logs
 */
int y_close_logs();

Log a message

To log a message, use the function y_log_message, defined by:

/**
 * Log a message using current parameters
 */
void y_log_message(const unsigned long type, const char * message, ...);

This function uses printf prototype for the message and the log message type. For example:

y_log_message(Y_LOG_LEVEL_INFO, "Initializing application");
y_log_message(Y_LOG_LEVEL_ERROR, "Error in application, you have %d over %d threads in error mode", threads_error, threads_total);

Example source code

See examples folder for detailed sample source codes.