SETBUF(3P)

💖 SETBUF(3P) — POSIX Programmer's Manual 💖

okay bestie, before we even start, a lil heads up from the PROLOG: this page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, go check the corresponding Linux manual page for the deets on Linux behavior), or honestly the interface may not be implemented on Linux at all. 🙈

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✨ NAME ✨

setbuf — assign buffering to a stream

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🌸 SYNOPSIS 🌸

#include <stdio.h>

void setbuf(FILE *restrict stream, char *restrict buf);

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🦋 DESCRIPTION 🦋

So the functionality on this reference page is aligned with the ISO C standard. If anything here conflicts with the ISO C standard, that conflict is not intentional, ok? This volume of POSIX.1‐2017 defers to the ISO C standard. periodt.

Other than the fact that it returns no value, this function call:

setbuf(stream, buf)

shall be equivalent to:

setvbuf(stream, buf, _IOFBF, BUFSIZ)

if buf is not a null pointer. And it's equivalent to:

setvbuf(stream, buf, _IONBF, BUFSIZ)

if buf is a null pointer. like, that's the whole vibe. 💅

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💜 RETURN VALUE 💜

The setbuf() function shall not return a value. not a single one. it's giving void and it's thriving.

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🔥 ERRORS 🔥

ngl, even though the setvbuf() interface may set errno in defined ways, the value of errno after a call to setbuf() is unspecified. so don't come for her about it. 😭

The following sections are informative. (translation: the tea below is bonus content, not requirements ✨)

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🎀 EXAMPLES 🎀

None. that's it. that's the section. 💀

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🌈 APPLICATION USAGE 🌈

A super common source of error is allocating buffer space as an "automatic" variable in a code block, and then failing to close the stream in that same block. bestie please. close the stream. 🫶

Also, with setbuf(), allocating a buffer of BUFSIZ bytes does not necessarily imply that all of BUFSIZ bytes are used for the buffer area. so like, don't assume the whole thing gets used.

And since errno is not required to be unchanged on success, if you actually wanna correctly detect and possibly recover from errors, applications should use setvbuf() instead of setbuf(). this is the main character move. 👑

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⭐ RATIONALE ⭐

None. iconic of her honestly.

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🧚 FUTURE DIRECTIONS 🧚

None.

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👑 SEE ALSO 👑

• Section 2.5, Standard I/O Streams
• fopen()
• setvbuf()

The Base Definitions volume of POSIX.1‐2017, <stdio.h>

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💅 COPYRIGHT 💅

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 .

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 whole page, bestie 🫶 this lil drop of the POSIX Programmer's Manual is brought to you by IEEE/The Open Group, dated 2017, and if you ever need to cite her, that's your source, your version and your date right there. slay. 🌸✨💖