Another important caveat to snprintf: because glibc's snprintf might use dynamic memory allocation it's not async-signal-safe. OpenBSD notably rewrote their snprintf implementation to be async-signal-safe (with the exception of floating-point formatting). They did this so extension functions like dprintf(), commonly used in signal handlers for debugging or logging, would be easier to implement, and also because a lot of software assumes that (or doesn't even consider whether) snprintf is async-signal-safe.

I wonder whether glibc's dprintf() is async-signal-safe....