SETBUF(3POSIX)

🌸 SETBUF(3POSIX) — the POSIX Programmer's Manual, bestie edition 🌸

okay so real talk, this page lives in the POSIX Programmer's Manual. That's the POSIX one, not the Linux one. The Linux implementation of this interface may differ (so like, go read the corresponding Linux manual page for the deets on Linux behavior), or honestly the interface might not even be implemented on Linux at all. 🙈 iykyk.

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✨ PROLOG ✨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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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 💅

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2017 defers to the ISO C standard.

So here's the tea ☕ — except 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, or to:

setvbuf(stream, buf, _IONBF, BUFSIZ)

if buf is a null pointer.

fr fr, that's the whole vibe. no return value, just pure side effects ✨

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🦋 RETURN VALUE 🦋

The setbuf() function shall not return a value.

like, it literally cannot give you anything back. it's giving void energy. 💀

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🌈 ERRORS 🌈

Although the setvbuf() interface may set errno in defined ways, the value of errno after a call to setbuf() is unspecified.

not me checking errno after setbuf()… bestie don't. it's unspecified. that's the whole point. 😭

The following sections are informative.

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🍓 EXAMPLES 🍓

None.

sadly. no examples. we move. 💅

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🧚 APPLICATION USAGE 🧚

A common source of error is allocating buffer space as an ``automatic'' variable in a code block, and then failing to close the stream in the same block.

With setbuf(), allocating a buffer of BUFSIZ bytes does not necessarily imply that all of BUFSIZ bytes are used for the buffer area.

Since errno is not required to be unchanged on success, in order to correctly detect and possibly recover from errors, applications should use setvbuf() instead of setbuf().

🚨 okay this is the important one bestie: if you actually need to catch errors and bounce back from them, use setvbuf(). setbuf() is not the one for that. periodt.

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⭐ RATIONALE ⭐

None.

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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 🫶 slay, go buffer responsibly — brought to you by IEEE/The Open Group, 2017, page SETBUF(3POSIX). 💜