Is there any log library for C? (like log4j for C)

Question

I've been working in Java for a long time, and I've been accostumed to use the log4j library for logs. It's a wonderful, and now that I'm moving to C I'd like to find if there is a similar library for logs in this language.

Answer 1

So far I know of the following libraries for logging: log4c, sclog4c, syslog, zlog.

log4c

log4c was invented to be a Log4J for C. If you're specifically looking for "something like Log4J" because you want it to be like "Log4J", this is most likely what you're looking for.

Links

• http://log4c.sourceforge.net/

sclog4c

sclog4c was invented to be as simple as the most frequently used features of java.util.logging - as simple as possible. If you're looking for "something like Log4J" because you want it to be as small and simple as possible, this is most likely what you're looking for.

Links

• https://github.com/christianhujer/sclog4c

syslog

syslog was originally developed by Eric Allman as part of sendmail and has become the defacto standard for daemon / server logging in POSIX environments. It is client-server based, usually the daemon that wants something to be logged will send the log data to a syslogd listening on UDP port 514. If you're specifically looking for "something like Log4J" because you actually want to log a daemon or server, this is most likely what you're looking for.

Links

• http://tools.ietf.org/html/rfc5424
• http://man7.org/linux/man-pages/man3/syslog.3.html
• http://en.wikipedia.org/wiki/Syslog

zlog

This one was invented to be like log4c, just - according to its description - smaller and more flexible at the same time.

Links

• https://github.com/HardySimpson/zlog

Miscellaneous

Power vs. Lean

Because of the different way how C links, thinks and works, I would not look for a logging framework which is powerful in a general case - unlike in Java. If you're going for "full-blown desktop applications" and beyond, logging with powerful frameworks like in Java is certainly a good way to go. If you're implementing command line tools or similar, I bet that a lean framework is better - why would you want to depend on lib2xml just for the sake of logging...

Speed

In case speed resp. not wasting cycles matters to you for some reason, look for a logging framework which uses macros to evaluate the log level before the other arguments are evaluated.

The downside is that you cannot call a log routine with arguments that have side-effects. But this shouldn't be a use case anyway. It would be astonishing if log statements were not ignorable because of containing side-effects.

The upside is that log statements in such a framework add so few cycles that they're almost not there - just an access to a global, a check and a conditional branch, skipping the rest of the log code - 2 instructions, 1 cycle in the best case on many of today's CPUs.

Disclaimer

I am the author of sclog4c.

Answer 2

Another option to consider is zf_log:

• Debug logging is reduced to no-op in release builds (compiled out)
• 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
• Optional built-in support for Android log and Apple system log (iOS, OS X)
• Custom output functions (file, syslog, etc.)

For example, that will output INFO log message:

ZF_LOGI("Number of arguments: %i", argc);

Which will look like:

04-29 22:43:20.244 40059  1299 I hello.MAIN main@hello.c:9 Number of arguments: 1

Exact representation is configurable and depends on build type (debug / release).

Answer 3

There is a log4c C library that mimics the log4j Java library. From the log4c documentation:

It is modeled after the Log for Java library staying as close to their API as is reasonable.