---
name: "CURLOPT_IOCTLDATA"
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/CURLOPT_IOCTLDATA"
---

# CURLOPT\_IOCTLDATA(3)

pointer passed to I/O callback

## NAME

CURLOPT\_IOCTLDATA - pointer passed to I/O callback

## SYNOPSIS

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

## DESCRIPTION

Pass the *pointer* that is untouched by libcurl and passed as the 3rd argument in the ioctl callback set with *[CURLOPT\_IOCTLFUNCTION(3)](/CURLOPT_IOCTLFUNCTION/3.md)*.

## DEFAULT

NULL

## PROTOCOLS

This functionality affects all supported protocols

## EXAMPLE

```
#include <unistd.h> /* for lseek */
struct data {
  int fd; /* our file descriptor */
};
static curlioerr ioctl_callback(CURL *handle, int cmd, void *clientp)
{
  struct data *io = (struct data *)clientp;
  if(cmd == CURLIOCMD_RESTARTREAD) {
    lseek(io->fd, 0, SEEK_SET);
    return CURLIOE_OK;
  }
  return CURLIOE_UNKNOWNCMD;
}
int main(void)
{
  struct data ioctl_data;
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_IOCTLFUNCTION, ioctl_callback);
    curl_easy_setopt(curl, CURLOPT_IOCTLDATA, &ioctl_data);
  }
}
```

## DEPRECATED

Deprecated since 7.18.0.

## AVAILABILITY

Added in curl 7.12.3

## RETURN VALUE

*[curl\_easy\_setopt(3)](/curl_easy_setopt/3.md)* returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**CURLOPT\_IOCTLFUNCTION**(3)](/CURLOPT_IOCTLFUNCTION/3.md), [**CURLOPT\_SEEKFUNCTION**(3)](/CURLOPT_SEEKFUNCTION/3.md)