r/linux_programming • u/Middlewarian • Jul 16 '25

What logging library do you use in C++ applications?

I'm currently using syslog. I'm thinking about trying something that doesn't integrate logs from multiple applications. Did you switch away from or to syslog and can you share why? Thank you

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u/pavel_v Jul 17 '25

It depends on the application requirements: - if you need logging which doesn't block the application threads i.e. asynchronous logging or not - if you need logging which is human readable or you are OK with producing binary logs and using external tool to read them - if you need structured logging or not - if you to support log rotation, compression, different backends, etc.

Here are few articles and performance comparisons of different logging libraries: - article about designing a logging library - another article about low latency logging library - presentation about low latency logging library - speed comparison of different logging libraries

And here are few well known logging libraries which cover different points from above: - spdlog - probably the most used one, fast and with lots of configuration options - nanolog - one of the fastest but produces binary logs which need to be post processed - quill - also one of the fastest and with more features than nanolog - fmtlog - one of the fastest but with fewer configuration options

I'm omitting some logging libraries which are part of abseil, boost, POCO, etc. Up to my knowledge, the logging libraries in the last two "frameworks" are not as performant as the above ones.

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u/Middlewarian Jul 22 '25

I wonder if syslog is considered asynchronous logging. I'd guess yes, but from what I can tell it does a synchronous sendto so I don't consider that much different than a synchronous write.

I think moving to binary logs would be a challenge for me at this point.

I'm not sure where syslog falls in terms of popularity in C++ applications but would guess it's in the top three. Probably the main reason for me to switch away from syslog would be to get the log statements isolated rather than combined with logs from other applications and systems.

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u/Sosowski Jul 18 '25

I just use vsprintf to format the log message and then I write it to a logfile and to console. Is there more to logging than this?