CURLMOPT\_SOCKETDATA(3) Library Functions Manual CURLMOPT\_SOCKETDATA(3)

# [NAME](#NAME)

CURLMOPT\_SOCKETDATA - custom pointer passed to the socket callback

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_SOCKETDATA, void *pointer);
```

# [DESCRIPTION](#DESCRIPTION)

A data *pointer* to pass to the socket callback set with the [*CURLMOPT\_SOCKETFUNCTION(3)*](/man/os/curl/CURLMOPT_SOCKETFUNCTION.3) option.

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

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects all supported protocols

# [EXAMPLE](#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](#AVAILABILITY)

Added in curl 7.15.4

# [RETURN VALUE](#RETURN_VALUE)

Returns CURLM\_OK.

# [SEE ALSO](#SEE_ALSO)

[**CURLMOPT\_SOCKETFUNCTION**(3)](/man/os/curl/CURLMOPT_SOCKETFUNCTION.3), [**CURLMOPT\_TIMERFUNCTION**(3)](/man/os/curl/CURLMOPT_TIMERFUNCTION.3), [**curl\_multi\_socket\_action**(3)](/man/os/curl/curl_multi_socket_action.3)

2026-10-19 libcurl

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Document: CURLMOPT_SOCKETDATA(3) from curl 8.23.0-r1 (Chainguard OS)
Source: https://github.com/curl/curl.git