CURLOPT_IOCTLDATA - pointer passed to I/O callback

Added in curl 7.12.3

NULL

Deprecated since 7.18.0.

Pass the pointer that is untouched by libcurl and passed as the 3rd argument in the ioctl callback set with CURLOPT_IOCTLFUNCTION(3).

#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); } }

CURLOPT_IOCTLDATA - pointer passed to I/O callback

This functionality affects all supported protocols

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).

CURLOPT_IOCTLFUNCTION(3), CURLOPT_SEEKFUNCTION(3) libcurl 2025-06-16 CURLOPT_IOCTLDATA(3)

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