CURLOPT_IOCTLDATA(3)       Library Functions Manual       CURLOPT_IOCTLDATA(3)

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).

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) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLOPT_IOCTLFUNCTION(3), CURLOPT_SEEKFUNCTION(3)

libcurl                           2025-07-16              CURLOPT_IOCTLDATA(3)