Log4c : Logging for C Library

1.2.1

Summary Requirements Installation Configuration Customization Thanks Copyright

Summary

Log4c is a library of C for flexible logging to files, syslog and other destinations. It is modeled after the Log for Java library (http://jakarta.apache.org/log4j/), staying as close to their API as is reasonable. Here is a short introduction to Log4j which describes the API, and design rationale.

Mark Mendel started a parallel log4c projet with a different philosophy. The design is macro oriented, so much lighter and faster which perfect for kernel development.

Log4c is also available from SourceForge (http://www.sourceforge.net/projects/log4c/). This is work in progress.

Requirements

Platforms

log4c was successfully compiled and run on the following platforms :

HP-UX release 11.00
Tru 64 release 4.0F and 5.1
Red Hat Linux Intel release 7.x, 8, 9
Red Hat Enterprise Linux 3, 4
Solaris Intel release 8, 9, 10
FreeBSD 6.1-RELEASE
AIX 5.3 (witk xlc compiler)
Mac OS X
Windows X

log4c should compile and run on the following platforms :

The BSD family
Other Linux distributions

Software

The following softwares are needed to generate log4c:

GCC 3.0.1+, to generate log4c, but hopefully not to use it.
doxygen 1.2.13+, a documentation system for C/C++ needed to generate the documentation.
graphviz, the AT&T Graph Visualization Tools also needed to generate the documentation.

For the moment, log4c uses specific GCC extensions, like __attribute__, so you will need GCC to compile it. This will probably change one day.

Installation

Building from source tarballs

on SourceForge:

log4c-1.2.1.tar.gz

The log4c package uses the GNU autotools compilation and installation framework. The following commands should build log4c on the supported platforms:

$ gzip -dc log4c-1.2.1.tar.gz | tar tvf -
$ cd log4c-1.2.1/
$ ./configure --prefix=/path/of/installation
$ make
$ make install

Checkout the INSTALL file for installation and the generated doxygen documentation for more information.

Using RPMs

FC7 RPMs on SourceForge:

The following command install the log4c RPMs :

$ sudo rpm -Uvh log4c-1.2.1.i386.rpm log4c-devel-1.2.1.i386.rpm

Configuration

Configuration files

log4c searches the folloging files to load its configuration:

${LOG4C_RCPATH}/log4crc
${HOME}/.log4crc
./log4crc

The environment variable LOG4C_RCPATH holds the prefix used for installation.

Configuration syntax

The log4crc configuration file uses an XML syntax. The root element is <log4c> and it can be used to control the configuration file version interface with the attribute "version". The following 4 elements are supported: <config>, <category>, <appender> and <layout>.

The <config> element controls the global log4c configuration. It has 3 sub elements. The <nocleanup> flag inhibits the log4c destructors routines. The <bufsize> element sets the buffer size used to format log4c_logging_event_t objects. If is set to 0, the allocation is dynamic (the <debug> element is currently unused).

The <category> element has 3 possible attributes: the category "name", the category "priority" and the category "appender". Future versions will handle multple appenders per category.

The <appender> element has 3 possible attributes: the appender "name", the appender "type", and the appender "layout".

The <layout> element has 2 possible attributes: the layout "name" and the layout "type".

Here's the default log4crc configuration file:

This initial version of the log4c configuration file syntax is quite different from log4j. XML seemed the best choice to keep the log4j configuration power in a C API.

Environment variables

LOG4C_RCPATH holds the path to the main log4crc configuration file
LOG4C_PRIORITY holds the "root" category priority
LOG4C_APPENDER holds the "root" category appender

Customization

This section will, one day, briefly describe how to define custom appenders and custom layouts. Be patient or checkout the source.

Thanks

Mark Mendel for his work on a previous version of log4c.

This project would not have existed without Ceki Gulcu, the creator and maintainer of Log4j, nor without Bastiaan Bakker, who intiated me with Log4Cpp.

Many thanks to

Joel Schaubert for many contributions
Robert Byrne for Windows port and also many contributions
Olger Warnier for the Mac OS X port
Jeff Smith for writing a primer on how to use Log4c effectively