sys_select.h(0P)

✨ sys_select.h — the select types header, bestie edition ✨

okay so real talk, this page is from the POSIX Programmer's Manual 💖 it's literally sys_select.h(0P). Before we even get into it, here's the lil prolog disclaimer:

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.

ngl that's the standard "this might not be your Linux, go check" warning and it applies fr fr 🙈

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🌸 NAME 🌸

sys/select.h — the header that gives you the select types 🦋

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🎀 SYNOPSIS 🎀

#include <sys/select.h>

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💅 DESCRIPTION 💅

Okay so this header is lowkey the whole vibe for select()-style waiting on file descriptors, and here's every single thing it's gotta define, no cap:

The <sys/select.h> header shall define the timeval structure, which shall include at least these members:

time_t         tv_sec      Seconds.
suseconds_t    tv_usec     Microseconds.

The <sys/select.h> header shall define the time_t and suseconds_t types as described in <sys/types.h>. 💖

The <sys/select.h> header shall define the sigset_t type as described in <signal.h>.

The <sys/select.h> header shall define the timespec structure as described in <time.h>.

The <sys/select.h> header shall define the fd_set type as a structure. 👑

And it shall define this one symbolic constant, and its value has to be suitable for use in #if preprocessing directives:

• FD_SETSIZE — Maximum number of file descriptors in an fd_set structure.

Now for the icons themselves — the following shall be declared as functions, defined as macros, or both. If functions are declared, function prototypes shall be provided:

void FD_CLR(int, fd_set *);
int  FD_ISSET(int, fd_set *);
void FD_SET(int, fd_set *);
void FD_ZERO(fd_set *);

⚠️ bestie listen — if these are implemented as macros, they may evaluate their arguments more than once, so applications should ensure that the arguments they supply are never expressions with side-effects. like fr, don't be passing i++ in there, that's giving chaos 💀

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided:

int  pselect(int, fd_set *restrict, fd_set *restrict, fd_set *restrict,
         const struct timespec *restrict, const sigset_t *restrict);
int  select(int, fd_set *restrict, fd_set *restrict, fd_set *restrict,
         struct timeval *restrict);

Also, heads up: inclusion of the <sys/select.h> header may make visible all symbols from the headers <signal.h> and <time.h>. surprise guests at the party 🎉🫶

The following sections are informative. (iykyk, that means they're the commentary track, not the rules ✨)

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🌈 APPLICATION USAGE 🌈

None. literally nothing, it said what it said 🙈

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🧚 RATIONALE 🧚

None. also nothing. iconic behaviour tbh 💅

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⭐ FUTURE DIRECTIONS ⭐

None. no plans, no glow-up scheduled, we stay as we are 🌸

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🔥 SEE ALSO 🔥

• <signal.h>
• <sys_time.h>
• <sys_types.h>
• <time.h>

The System Interfaces volume of POSIX.1‐2017, pselect()

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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 absolute icon of a header page was brought to you by IEEE/The Open Group, dated 2017 — go off, standard setters 👑✨