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* Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
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CURLOPT_RESOLVER_START_DATA - custom pointer passed to the resolver start callback #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_RESOLVER_START_DATA, void *pointer); Pass a pointer that will be untouched by libcurl and passed as the third argument in the resolver start callback set with CURLOPT_RESOLVER_START_FUNCTION(3). NULL All

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;
}

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, "http://example.com");
 curl_easy_perform(curl);
 curl_easy_cleanup(curl);
}

Added in 7.59.0 Returns CURLE_OK CURLOPT_RESOLVER_START_FUNCTION "(3) "