@node select
@subsection @code{select}
@findex select

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/select.html}

Gnulib module: select
@mindex select

Portability problems fixed by Gnulib:
@itemize
@item
This function is declared in @code{<winsock2.h>}
instead of @code{<sys/select.h>}
on some platforms:
mingw, MSVC 14.
@item
On Windows platforms (excluding Cygwin), @code{select} can only be
called on descriptors created by the @code{socket} function, not on regular
file descriptors.
@item
On Windows platforms (excluding Cygwin), error codes from this function
are not placed in @code{errno}, and @code{WSAGetLastError} must be used
instead.
@item
On some platforms, this function fails to detect invalid fds with
EBADF, but only if they lie beyond the current maximum open fd:
FreeBSD 8.2.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
When you call @code{select} with a timeout, some implementations modify the
timeout parameter so that upon return from the function, it contains the
amount of time not slept.  Other implementations leave the timeout parameter
unmodified.
@item
Under Windows, when passing a pipe, Gnulib's @code{select} replacement might
return 0 even before the timeout has passed.  Programs using it with pipes can
thus busy wait.
@item
On Linux, when some file descriptor refers to a regular file, @code{select}
may fail, setting @code{errno} to @code{EBADF}.
@item
On Haiku,
@c https://dev.haiku-os.org/ticket/19220
the maximum allowed value for the first argument is not @code{FD_SETSIZE}
but @code{FD_SETSIZE / 2}.
@end itemize
