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curl_multi_waitfds(3)	    Library Functions Manual	   curl_multi_waitfds(3)

NAME
     curl_multi_waitfds  - extract file descriptor information from a multi han-
     dle

SYNOPSIS
     #include <curl/curl.h>
     #include <stdlib.h>

     CURLMcode curl_multi_waitfds(CURLM *multi,
				  struct curl_waitfd *ufds,
				  unsigned int size,
				  unsigned int *fd_count);

DESCRIPTION
     This  function  extracts  curl_waitfd  structures	which  are  similar   to
     poll(2)'s pollfd structure from a given multi_handle.

     These  structures	can be used for polling on multi_handle file descriptors
     in a fashion similar to curl_multi_poll(3). The curl_multi_perform(3) func-
     tion should be called as soon as one of them is ready to be  read	from  or
     written to.

     libcurl  fills provided ufds array up to the size.  If a number of descrip-
     tors used by the multi_handle is  greater	than  the  size  parameter  then
     libcurl returns CURLM_OUT_OF_MEMORY error.

     If  the  fd_count	argument  is not a null pointer, it points to a variable
     that on return specifies the number of descriptors used by the multi_handle
     to be checked for being ready to read or write.

     The client code can pass size equal to zero to get the number  of	the  de-
     scriptors	and allocate appropriate storage for them to be used in a subse-
     quent function call. In this case, fd_count receives a number greater  than
     or equal to the number of descriptors.

PROTOCOLS
     This functionality affects all supported protocols

EXAMPLE
     #include <stdlib.h>

     int main(void)
     {
       CURLMcode mresult;
       struct curl_waitfd *ufds;

       CURLM *multi = curl_multi_init();

       do {
	 /* call curl_multi_perform() */

	 /* get the count of file descriptors from the transfers */
	 unsigned int fd_count = 0;

	 mresult = curl_multi_waitfds(multi, NULL, 0, &fd_count);

	 if(mresult != CURLM_OK) {
	   fprintf(stderr, "curl_multi_waitfds() failed, code %d.\n", mresult);
	   break;
	 }

	 if(!fd_count)
	   continue; /* no descriptors yet */

	 /* allocate storage for our descriptors */
	 ufds = malloc(fd_count * sizeof(struct curl_waitfd));

	 /* get wait descriptors from the transfers and put them into array. */
	 mresult = curl_multi_waitfds(multi, ufds, fd_count, &fd_count);

	 if(mresult != CURLM_OK) {
	   fprintf(stderr, "curl_multi_waitfds() failed, code %d.\n", mresult);
	   free(ufds);
	   break;
	 }

	 /* Do polling on descriptors in ufds */

	 free(ufds);
       } while(!mresult);
     }

AVAILABILITY
     Added in curl 8.8.0

RETURN VALUE
     This function returns a CURLMcode indicating success or error.

     CURLM_OK (0) means everything was OK, non-zero means an error occurred, see
     libcurl-errors(3).

SEE ALSO
     curl_multi_fdset(3),	curl_multi_perform(3),	     curl_multi_poll(3),
     curl_multi_wait(3)

libcurl 			   2026-06-11		   curl_multi_waitfds(3)

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