curl_multi_fdset - extracts file descriptor information from a multi handle


#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);


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 curl_multi_fdset(3) only adds its own descriptors, it doesn’t zero or otherwise remove any others. The curl_multi_perform(3) function should be called as soon as one of them is ready to be read from or written to.

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

You should also be aware that when doing select(), you should consider using a rather small (single-digit number of seconds) timeout and call curl_multi_perform regularly - even if no activity has been seen on the fd_sets - as otherwise libcurl-internal retries and timeouts may not work as you’d think and want.

Starting with libcurl 7.16.0, you should use curl_multi_timeout to figure out how long to wait for action.


CURLMcode type, general libcurl multi interface error code. See libcurl-errors(3)


curl_multi_cleanup(3), curl_multi_init(3), curl_multi_timeout(3)

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