CURLOPT\_SOCKOPTDATA(3) Library Functions Manual CURLOPT\_SOCKOPTDATA(3)

# [NAME](#NAME)

CURLOPT\_SOCKOPTDATA - pointer to pass to sockopt callback

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SOCKOPTDATA, void *pointer);
```

# [DESCRIPTION](#DESCRIPTION)

Pass a *pointer* that is untouched by libcurl and passed as the first argument in the sockopt callback set with [*CURLOPT\_SOCKOPTFUNCTION(3)*](/man/os/curl/CURLOPT_SOCKOPTFUNCTION.3).

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects all supported protocols

# [EXAMPLE](#EXAMPLE)

```
static int sockopt_callback(void *clientp, curl_socket_t curlfd,


                            curlsocktype purpose)
{


  int val = *(int *)clientp;


  setsockopt((int)curlfd, SOL_SOCKET, SO_RCVBUF,


             (const char *)&val, sizeof(val));


  return CURL_SOCKOPT_OK;
}
int main(void)
{


  CURL *curl = curl_easy_init();


  if(curl) {


    CURLcode result;


    int recvbuffersize = 256 * 1024;


    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");


    /* call this function to set options for the socket */


    curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);


    curl_easy_setopt(curl, CURLOPT_SOCKOPTDATA, &recvbuffersize);


    result = curl_easy_perform(curl);


    curl_easy_cleanup(curl);


  }
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.16.0

# [RETURN VALUE](#RETURN_VALUE)

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

# [SEE ALSO](#SEE_ALSO)

[**CURLOPT\_OPENSOCKETFUNCTION**(3)](/man/os/curl/CURLOPT_OPENSOCKETFUNCTION.3), [**CURLOPT\_SOCKOPTFUNCTION**(3)](/man/os/curl/CURLOPT_SOCKOPTFUNCTION.3)

2026-10-19 libcurl

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