romenskiy2012/curl

mirror of https://github.com/curl/curl.git synced 2026-04-30 02:07:50 +03:00

Daniel Stenberg 54ded66618

docs/libcurl: improve easy setopt examples

- always assign the curl_easy_perform() return code (and declare
  the necessary 'result' variable for it)

- always call curl_easy_cleanup() on the created easy handles

Closes #21364

2026-04-18 23:34:39 +02:00

2.1 KiB

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SPDX-License-Identifier

Title

Section

Source

See-also

Protocol

Added-in

curl

CURLOPT_RESOLVER_START_FUNCTION

libcurl

CURLOPT_PREREQFUNCTION (3)

CURLOPT_RESOLVER_START_DATA (3)

All

7.59.0

NAME

CURLOPT_RESOLVER_START_FUNCTION - callback called before a new name resolve is started

SYNOPSIS

#include <curl/curl.h>

int resolver_start_cb(void *resolver_state, void *reserved, void *userdata);

CURLcode curl_easy_setopt(CURL *handle,
                          CURLOPT_RESOLVER_START_FUNCTION,
                          resolver_start_cb);

DESCRIPTION

Pass a pointer to your callback function, which should match the prototype shown above.

This callback function gets called by libcurl every time before a new resolve request is started.

resolver_state points to a backend-specific resolver state. Currently only the ares resolver backend has a resolver state. It can be used to set up any desired option on the ares channel before it is used, for example setting up socket callback options.

reserved is reserved.

userdata is the user pointer set with the CURLOPT_RESOLVER_START_DATA(3) option.

The callback must return 0 on success. Returning a non-zero value causes the resolve to fail.

DEFAULT

NULL (No callback)

%PROTOCOLS%

EXAMPLE

static int 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) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, start_cb);
    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_DATA, curl);
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

%AVAILABILITY%

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).

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