curl/docs/libcurl/curl_multi_fdset.3

.\"
.TH curl_multi_fdset 3 "2 Jan 2006" "libcurl 7.16.0" "libcurl Manual"
.SH NAME
curl_multi_fdset - extracts file descriptor information from a multi handle
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLMcode curl_multi_fdset(CURLM *multi_handle,
                           fd_set *read_fd_set,
                           fd_set *write_fd_set,
                           fd_set *exc_fd_set,
                           int *max_fd);
.ad
.SH DESCRIPTION
This function extracts file descriptor information from a given multi_handle.
libcurl returns its fd_set sets. The application can use these to select() on,
but be sure to FD_ZERO them before calling this function as
\fIcurl_multi_fdset(3)\fP only adds its own descriptors, it doesn't zero or
otherwise remove any others. The \fIcurl_multi_perform(3)\fP function should be
called as soon as one of them is ready to be read from or written to.

To be sure to have up-to-date results, you should call
\fIcurl_multi_perform\fP until it does not return CURLM_CALL_MULTI_PERFORM
prior to calling \fIcurl_multi_fdset\fP.  This will make sure that libcurl has
updated the handles' socket states.

If no file descriptors are set by libcurl, \fImax_fd\fP will contain -1 when
this function returns. Otherwise it will contain the higher descriptor number
libcurl set.

When doing select(), you should use \fBcurl_multi_timeout\fP to figure out how
long to wait for action. Call \fIcurl_multi_perform\fP even if no activity has
been seen on the fd_sets after the timeout expires as otherwise internal
retries and timeouts may not work as you'd think and want.
.SH RETURN VALUE
CURLMcode type, general libcurl multi interface error code. See
\fIlibcurl-errors(3)\fP
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
.BR curl_multi_timeout "(3), " curl_multi_perform "(3) "