#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);


multi_handle Pointer to a multi handle.
read_fd_set Pointer to a read file descriptor set.
write_fd_set Pointer to a write file descriptor set.
exc_fd_set Pointer to an exc fd set.
max_fd Pointer to the maximum number of file descriptors.

Return Values

If the operation was successful, CURLM_OK is returned. Otherwise, a specific CURLM libcurl Error Code is returned.


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 only adds its own descriptors, it does not zero or otherwise remove any others. The curl_multi_perform function should be called as soon as one of them is ready to be read from or written to.

To ensure up-to-date results, call curl_multi_perform until it does not return CURLM_CALL_MULTI_PERFORM prior to calling curl_multi_fdset. This will ensure that libcurl has updated the handles' socket states.

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.

When doing select, use curl_multi_timeout to determine how long to wait for action. Call curl_multi_perform even if no activity has been seen on the fd_sets after the timeout expires. Otherwise, internal retries and timeouts may not work as expected.

Do Not Call From


See Also

HTTP Client Library (libcurl)
libcurl API Functions
libcurl Error Codes

Revision History

2013/09/18 Conversion
2013/05/08 Automated cleanup pass.
2012/05/04 Initial version.