CURLMOPT_SOCKETDATA(3) - Man pages

CURLMOPT_SOCKETDATA(3)      Library Functions Manual     CURLMOPT_SOCKETDATA(3)

NAME
       CURLMOPT_SOCKETDATA - custom pointer passed to the socket callback

SYNOPSIS
       #include <curl/curl.h>

       CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_SOCKETDATA, void *pointer);

DESCRIPTION
       A  data  pointer  to  pass  to  the  socket  callback set with the CURL-
       MOPT_SOCKETFUNCTION(3) option.

       This pointer is not touched by libcurl but is  only  passed  in  as  the
       socket callback's clientp argument.

DEFAULT
       NULL

PROTOCOLS
       This functionality affects all supported protocols

EXAMPLE
       struct priv {
         void *ours;
       };

       static int sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
       {
         struct priv *p = sockp;
         printf("my ptr: %p\n", p->ours);

         if(what == CURL_POLL_REMOVE) {
           /* remove the socket from our collection */
         }
         if(what & CURL_POLL_IN) {
           /* wait for read on this socket */
         }
         if(what & CURL_POLL_OUT) {
           /* wait for write on this socket */
         }

         return 0;
       }

       int main(void)
       {
         struct priv setup;
         CURLM *multi = curl_multi_init();
         /* ... use socket callback and custom pointer */
         curl_multi_setopt(multi, CURLMOPT_SOCKETFUNCTION, sock_cb);
         curl_multi_setopt(multi, CURLMOPT_SOCKETDATA, &setup);
       }

AVAILABILITY
       Added in curl 7.15.4

RETURN VALUE
       Returns CURLM_OK.

SEE ALSO
       CURLMOPT_SOCKETFUNCTION(3),                   CURLMOPT_TIMERFUNCTION(3),
       curl_multi_socket_action(3)

libcurl                            2026-07-12            CURLMOPT_SOCKETDATA(3)

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