---
name: "CURLOPT_CLOSESOCKETFUNCTION"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_CLOSESOCKETFUNCTION"
---

# CURLOPT\_CLOSESOCKETFUNCTION(3)

callback to socket close replacement

## NAME

CURLOPT\_CLOSESOCKETFUNCTION - callback to socket close replacement

## SYNOPSIS

```
#include <curl/curl.h>
int closesocket_callback(void *clientp, curl_socket_t item);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CLOSESOCKETFUNCTION,
                          closesocket_callback);
```

## DESCRIPTION

Pass a pointer to your callback function, which should match the prototype shown above.

This callback function gets called by libcurl instead of the *close(3)* or *closesocket(3)* call when sockets are closed (not for any other file descriptors). This is pretty much the reverse to the *[CURLOPT\_OPENSOCKETFUNCTION(3)](/CURLOPT_OPENSOCKETFUNCTION/3.md)* option. Return 0 to signal success and 1 if there was an error.

The *clientp* pointer is set with *[CURLOPT\_CLOSESOCKETDATA(3)](/CURLOPT_CLOSESOCKETDATA/3.md)*. *item* is the socket libcurl wants to be closed.

## DEFAULT

By default libcurl uses the standard socket close function.

## PROTOCOLS

All

## EXAMPLE

```
struct priv {
  void *custom;
};
static int closesocket(void *clientp, curl_socket_t item)
{
  struct priv *my = clientp;
  printf("our ptr: %p\n", my->custom);
  printf("libcurl wants to close %d now\n", (int)item);
  return 0;
}
int main(void)
{
  struct priv myown;
  CURL *curl = curl_easy_init();
  /* call this function to close sockets */
  curl_easy_setopt(curl, CURLOPT_CLOSESOCKETFUNCTION, closesocket);
  curl_easy_setopt(curl, CURLOPT_CLOSESOCKETDATA, &myown);
  curl_easy_perform(curl);
  curl_easy_cleanup(curl);
}
```

## AVAILABILITY

Added in 7.21.7

## RETURN VALUE

Returns CURLE\_OK if the option is supported, and CURLE\_UNKNOWN\_OPTION if not.

## SEE ALSO

[**CURLOPT\_CLOSESOCKETDATA**(3)](/CURLOPT_CLOSESOCKETDATA/3.md), [**CURLOPT\_OPENSOCKETFUNCTION**(3)](/CURLOPT_OPENSOCKETFUNCTION/3.md)