CURLOPT_RESOLVER_START_DATA - pointer passed to the resolver start callback

Added in curl 7.59.0

NULL

Pass a pointer is be untouched by libcurl and passed as the third argument in the resolver start callback set with CURLOPT_RESOLVER_START_FUNCTION(3).

static int resolver_start_cb(void *resolver_state, void *reserved, void *userdata) { (void)reserved; printf("Received resolver_state=%p userdata=%p\n", resolver_state, userdata); return 0; } int main(void) { CURL *curl = curl_easy_init(); if(curl) { curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, resolver_start_cb); curl_easy_setopt(curl, CURLOPT_RESOLVER_START_DATA, curl); curl_easy_setopt(curl, CURLOPT_URL, "https://example.com"); curl_easy_perform(curl); curl_easy_cleanup(curl); } }

CURLOPT_RESOLVER_START_DATA - pointer passed to the resolver start 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_PREREQFUNCTION(3), CURLOPT_RESOLVER_START_FUNCTION(3) libcurl 2025-06-16 CURLOPT_RESOLVER_START_DATA(3)

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