libcurl域名解析失败

#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, "http://example.com");

        // 设置 DNS 解析超时时间
        struct timeval timeout;
        timeout.tv_sec = 5;
        timeout.tv_usec = 0;
        curl_easy_setopt(curl, CURLOPT_DNS_CACHE_TIMEOUT, timeout.tv_sec);

        res = curl_easy_perform(curl);
        if(res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));

        curl_easy_cleanup(curl);
    }
    curl_global_cleanup();
    return 0;
}

#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, "http://example.com");

        // 设置代理
        curl_easy_setopt(curl, CURLOPT_PROXY, "http://proxy.example.com:8080");
        curl_easy_setopt(curl, CURLOPT_PROXYTYPE, CURLPROXY_HTTP);

        res = curl_easy_perform(curl);
        if(res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));

        curl_easy_cleanup(curl);
    }
    curl_global_cleanup();
    return 0;
}