I am trying to run below example with libcurl

#include <stdio.h>
#include <curl/curl.h>

int main(void)
{
    CURL* curl;
    CURLcode res;

    curl_global_init(CURL_GLOBAL_DEFAULT);

    curl = curl_easy_init();
   
    if (curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");

#ifdef SKIP_PEER_VERIFICATION
        /*
         * If you want to connect to a site who is not using a certificate that is
         * signed by one of the certs in the CA bundle you have, you can skip the
         * verification of the server's certificate. This makes the connection
         * A LOT LESS SECURE.
         *
         * If you have a CA cert for the server stored someplace else than in the
         * default bundle, then the CURLOPT_CAPATH option might come handy for
         * you.
         */
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
#endif

#ifdef SKIP_HOSTNAME_VERIFICATION
        /*
         * If the site you are connecting to uses a different host name that what
         * they have mentioned in their server certificate's commonName (or
         * subjectAltName) fields, libcurl refuses to connect. You can skip this
         * check, but it makes the connection insecure.
         */
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
#endif

        /* cache the CA cert bundle in memory for a week */
        auto resultThree = curl_easy_setopt(curl, CURLOPT_CA_CACHE_TIMEOUT, 604800L);

        /* Perform the request, res gets the return code */
        res = curl_easy_perform(curl);
        /* Check for errors */
        if (res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %sn",
                curl_easy_strerror(res));

        /* always cleanup */
        curl_easy_cleanup(curl);
    }

    curl_global_cleanup();

    return 0;
}

but I am getting the response as CURLE_UNSUPPORTED_PROTOCOL for curl_easy_perform. It looks like it can not process https response where as http response for "https://example.com/" is all good.

I referred to
Unsupported Protocol using Curl in C

curl -V does show me https and my cmakelist does show below (in block code), so I am sure it is built with SSL Library

if(WIN32)
  cmake_dependent_option(CURL_USE_SCHANNEL "Enable Windows native SSL/TLS" OFF CURL_ENABLE_SSL OFF)
  option(CURL_WINDOWS_SSPI "Enable SSPI on Windows" ${CURL_USE_SCHANNEL})
endif()

Next I have referred to How to Download the SSL Certificate From a Website in Windows and manually downloaded the server certificate as cacert.crt

Then I am trying to use curl_easy_setopt(curl, CURLOPT_CAINFO, cacert); as suggested in
Certificate Verification and CURLOPT_CAINFO
and accordingly my code looks like

curl = curl_easy_init();
    auto cacert = "C:\GauravK\CPP_17\CURL_CPP\CURL_CPP\cacert.crt";
    if (curl) {
        auto resultOne = curl_easy_setopt(curl, CURLOPT_CAINFO, const_cast<char*> (cacert));
        auto resultTwo = curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");

        /* cache the CA cert bundle in memory for a week */
        auto resultThree = curl_easy_setopt(curl, CURLOPT_CA_CACHE_TIMEOUT, 604800L);

        /* Perform the request, res gets the return code */
        res = curl_easy_perform(curl);

resultOne, resultTwo and resultThree are all CURLE_OK, but my res is still CURLE_UNSUPPORTED_PROTOCOL. I even tried to define SKIP_PEER_VERIFICATION and SKIP_HOSTNAME_VERIFICATION but no luck.

Can someone help please?