---
name: "CURLMOPT_SOCKETDATA"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLMOPT_SOCKETDATA"
---

# CURLMOPT\_SOCKETDATA(3)

custom pointer passed to the socket callback

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