FMT_COMPILE vs FMT_STRING vs ""_format()

[leolchat]

The documentation is not extremely clear about the difference between the 3 ways I found to have compile-time format string checks. I would like to try to PR an improvement to the documentation, but first I need to be sure

• Is there a difference as to what they can check? In my quick survey I could not find an example rejected by one but not the others.
• Is there a preferred one? Compiler verbose output seems shorter with the FMT_STRING version, but not using a macro is nice, or is the speed boost from FMT_COMPILE usually worth it?

Bonus question, is there one which has a chance to land in std::format?

[vitaut]

Is there a difference as to what they can check?

Yes, FMT_STRING always does compile-time checks while _format only if a compiler supports UDL templates extensions.

Is there a preferred one?

FMT_STRING and FMT_COMPILE serve different purposes. If you only need checks then use FMT_STRING. If you want to avoid format string parsing overhead then use FMT_COMPILE (this is rarely needed) and note that:

Format string compilation can generate more binary code compared to the default API and is only recommended in places where formatting is a performance bottleneck.

[leolchat]

Thanks for clarifying. I would say the documentation could be more explicit. I gave it a try.