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10.1269 vsnprintf

POSIX specification:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/vsnprintf.html

Gnulib module: vsnprintf or vsnprintf-posix or vsnprintf-gnu

Portability problems fixed by either Gnulib module vsnprintf or vsnprintf-posix or vsnprintf-gnu:

• This function does not support format directives that access arguments in an arbitrary order, such as "%2$s", on some platforms: NetBSD 3.0, mingw, MSVC 14.
• This function does not return a byte count as specified in C99 on some platforms: HP-UX 11, Solaris 9, mingw, MSVC 14.

Portability problems fixed by either Gnulib module vsnprintf-posix or vsnprintf-gnu:

• This function does not support size specifiers as in C99 (hh, ll, j, t, z) on some platforms: AIX 5.1, HP-UX 11.23, Solaris 9, Cygwin 1.5.24, old mingw, MSVC 9.
• This function does not support size specifiers as in C23 (w8, w16, w32, w64, wf8, wf16, wf32, wf64) on some platforms: glibc 2.37, musl libc, macOS 14, FreeBSD 13.2, NetBSD 10.0, OpenBSD 7.5, AIX 7.3, Solaris 11.4, Cygwin 3.5.3, mingw, MSVC, Android 9.0.
• printf of ‘long double’ numbers is unsupported on some platforms: mingw, MSVC 14.
• printf "%f", "%e", "%g" of Infinity and NaN yields an incorrect result on some platforms: AIX 7.3, Solaris 11.4, mingw, MSVC 14.
• This function does not support the ‘a’ and ‘A’ directives on some platforms: FreeBSD 5.2.1, OpenBSD 4.0, AIX 5.2, HP-UX 11, Solaris 11.4, Cygwin 1.5.x, mingw, MSVC 14.
• This function does not support the ‘b’ directive, required by ISO C23, on some platforms: glibc 2.34, musl libc, macOS 14, FreeBSD 13.2, NetBSD 10.0, OpenBSD 7.5, AIX 7.3, HP-UX 11, Solaris 11.4, Cygwin 3.5.3, mingw, MSVC 14, Android 9.0.
• This function does not support the ‘F’ directive on some platforms: NetBSD 3.0, AIX 5.1, HP-UX 11.23, Solaris 9, Cygwin 1.5.x, mingw, MSVC 14.
• This function does not support the ‘ls’ directive on some platforms: OpenBSD 4.0, Cygwin 1.5.x, Haiku.
• This function does not support precisions in the ‘ls’ directive correctly on some platforms: Solaris 11.4.
• This function doesn’t support the ' flag on some platforms: NetBSD 3.0, Cygwin 1.5.24, mingw, MSVC 14.
• This function does not round the argument of the ‘a’ directive correctly on some platforms: macOS 14, FreeBSD 14.0, NetBSD 10.0, OpenBSD 7.5, AIX 7.3, Solaris 11.4.
• printf "%010f" of NaN and Infinity yields an incorrect result (padded with zeroes, or wrong capitalization) on some platforms: Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, AIX 7.3, Solaris 11.4, Cygwin 1.5.x, mingw, MSVC/clang.
• printf "%#.0x" or "%#.0X" with a zero argument yields an incorrect result (non-empty) on some platforms: Mac OS X 10.6.
• This function does not support precisions larger than 512 or 1024 in integer, floating-point and pointer output on some platforms: AIX 7.1, Solaris 10/x86, mingw, MSVC/clang.
• This function mishandles large floating point precisions (for example, formatting 1.0 with ‘"%.511f"’) on some platforms: Solaris 10.
• This function produces wrong output for the ‘lc’ directive with a NUL wide character argument on some platforms: musl libc 1.2.4.
• This function can crash in out-of-memory conditions on some platforms: FreeBSD 14.0, NetBSD 5.0.
• This function does not truncate the result as specified in C99 on some platforms: mingw, MSVC 14.
• This function overwrites memory even when a zero size argument is passed on some platforms: HP-UX 11.

Portability problems fixed by Gnulib module vsnprintf-gnu:

• This function does not support the ‘B’ directive on some platforms: glibc 2.34, musl libc, macOS 14, FreeBSD 13.2, NetBSD 10.0, OpenBSD 7.5, AIX 7.3, Solaris 11.4, Cygwin 3.5.3, mingw, MSVC, Android 9.0.

Portability problems fixed by either Gnulib module vsnprintf-posix or vsnprintf-gnu and additionally the Gnulib module printf-with-n-directive:

• This function does not fully support the ‘n’ directive on some platforms: glibc when used with _FORTIFY_SOURCE >= 2 (set by default on Ubuntu), macOS 14, OpenBSD, HP-UX 11, mingw, MSVC 14, Android.

Portability problems not fixed by Gnulib:

• The %m directive is not portable, use %s mapped to an argument of strerror(errno) (or a version of strerror_r) instead.
• Formatting noncanonical ‘long double’ numbers produces nonmeaningful results on some platforms: glibc and others, on x86, x86_64, IA-64 CPUs.
• When formatting an integer with grouping flag, this function inserts thousands separators even in the "C" locale on some platforms: NetBSD 5.1.