Enabling Strict ANSI compile?
> I’m looking through GCC 5.3.0 manual but I can’t figure out where to find help with usage of the functions, or their implementations?
Those are not compiler-specific functions, those are standard C library functions, look in your libc documentation/reference.
BTW, why don’t you use the more common and well-known snprintf function?
FYI, gcvt and family are marked as LEGACY in POSIX.1-2001. POSIX.1-2008 removes the specification of gcvt(), recommending the use of sprintf(3) instead (though snprintf(3) may be preferable).
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