VFPRINTF(3POSIX)

✨ VFPRINTF(3POSIX) ✨

okay so bestie, buckle up 💖 this page lives inside the POSIX Programmer's Manual — that's the whole vibe — and it's all about five little functions that format stuff using a stdarg argument list instead of the usual variadic chaos. no cap, they're iconic.

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🌸 PROLOG

real talk first: this manual page is part of the POSIX Programmer's Manual. that's the source, periodt.

but heads up 👑 — the Linux implementation of this interface may differ (so like, go consult the corresponding Linux manual page for details of Linux behavior if you're actually on Linux, iykyk). or honestly? the interface might not be implemented on Linux at all. 🙈 so check before you commit.

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👑 NAME

vdprintf, vfprintf, vprintf, vsnprintf, vsprintf — they format output of a stdarg argument list. that's the whole gig, that's the assignment. 💅

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🦋 SYNOPSIS

#include <stdarg.h>
#include <stdio.h>

int vdprintf(int fildes, const char *restrict format, va_list ap);
int vfprintf(FILE *restrict stream, const char *restrict format,
    va_list ap);
int vprintf(const char *restrict format, va_list ap);
int vsnprintf(char *restrict s, size_t n, const char *restrict format,
    va_list ap);
int vsprintf(char *restrict s, const char *restrict format, va_list ap);

look at them. five little besties. all returning int. all taking a va_list ap. 🫶

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💖 DESCRIPTION

first things first — the functionality described on this reference page is aligned with the ISO C standard. and if anything here conflicts with the ISO C standard? that conflict is unintentional, it's not that deep. this volume of POSIX.1‐2017 defers to the ISO C standard. periodt.

so here's the tea ☕ — vdprintf(), vfprintf(), vprintf(), vsnprintf(), and vsprintf() shall be equivalent to the dprintf(), fprintf(), printf(), snprintf(), and sprintf() functions respectively. literally the same energy, same order, one-to-one:

• vdprintf() → dprintf()
• vfprintf() → fprintf()
• vprintf() → printf()
• vsnprintf() → snprintf()
• vsprintf() → sprintf()

the ONLY plot twist 🎀 is that instead of being called with a variable number of arguments, they get called with an argument list as defined by <stdarg.h>. that's it. that's the difference. main character twist, honestly.

now the important part, do NOT skip this ⚠️ — these functions shall not invoke the va_end macro. and because these functions invoke the va_arg macro, the value of ap after the return is unspecified. like, unspecified-unspecified. don't come for it, it's not gonna tell you. 💀

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⭐ RETURN VALUE

Refer to fprintf(). that's it, go read that one, she has the answers. 🦋

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💀 ERRORS

Refer to fprintf(). again. same page, same bestie.

also, lowkey important: the following sections are informative. (yes, that's a real thing, iykyk.)

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🌈 EXAMPLES

None. 😭 not a single one. we're thriving on vibes alone.

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🍓 APPLICATION USAGE

okay so if you're an application using these functions, you should call va_end(ap) afterwards to clean up. 🧹✨ yes, even though the functions themselves don't do it. clean up after yourself, bestie, that's just being a good citizen. 💅

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🧚 RATIONALE

None. nothing to explain. she said what she said. 🎀

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🔥 FUTURE DIRECTIONS

None. the future is uncertain but this section? empty. iconic. 👑

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💜 SEE ALSO

• Section 2.5, Standard I/O Streams, fprintf()
• The Base Definitions volume of POSIX.1‐2017, <stdarg.h>, <stdio.h>

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📜 COPYRIGHT

okay legal bestie moment, stay with me 📝 — Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

and one more 🫶 — any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the page, bestie!! 🌸 this whole thing was brought to you by IEEE/The Open Group, 2017 — they're the ones behind VFPRINTF(3POSIX) and honestly, we owe them everything. 💖 go format something cute. 🎀✨