C++使用curl库进行http请求的方法详解

#include <iostream>
#include <string>
#include <curl/curl.h>
#include <ctime>
#include <iomanip>
 
size_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* output) {
    size_t totalSize = size * nmemb;
    output->append(static_cast<char*>(contents), totalSize);
    return totalSize;
}
 
// 将日期字符串转换为指定格式
std::string formatDateString(const std::string& dateString) {
    std::tm t;
    std::istringstream iss(dateString);
    // 解析日期字符串
    iss >> std::get_time(&t, "%a, %d %b %Y %H:%M:%S %Z");
    if (iss.fail()) {
        return "";
    }
 
    std::ostringstream oss;
    // 格式化日期
    oss << std::put_time(&t, "%m%d%H%M%Y.%S");
    return oss.str();
}
 
int main() {
    CURL* curl;
    CURLcode res;
    std::string responseHeaders;
 
    curl_global_init(CURL_GLOBAL_DEFAULT);
 
    curl = curl_easy_init();
    if (curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://your-backend-server/current-time");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
        curl_easy_setopt(curl, CURLOPT_HEADERDATA, &responseHeaders);
        curl_easy_setopt(curl, CURLOPT_HEADER, 1L);
 
        res = curl_easy_perform(curl);
        if (res != CURLE_OK) {
            std::cerr << "Failed to perform request: " << curl_easy_strerror(res) << std::endl;
        } else {
            std::string dateHeader = "Date: ";
            size_t startPos = responseHeaders.find(dateHeader);
            if (startPos != std::string::npos) {
                startPos += dateHeader.length();
                size_t endPos = responseHeaders.find("\r
", startPos);
                std::string dateString = responseHeaders.substr(startPos, endPos - startPos);
 
                std::string formattedDate = formatDateString(dateString);
                if (!formattedDate.empty()) {
                    std::cout << "Formatted date: " << formattedDate << std::endl;
                } else {
                    std::cerr << "Failed to format date string." << std::endl;
                }
            } else {
                std::cerr << "Failed to extract server time from response headers." << std::endl;
            }
        }
 
        curl_easy_cleanup(curl);
    }
 
    curl_global_cleanup();
 
    return 0;
}

// 将日期字符串转换为指定格式（北京时间）
std::string formatDateString(const std::string& dateString) {
    std::tm t;
    std::istringstream iss(dateString);
    // 解析日期字符串
    iss >> std::get_time(&t, "%a, %d %b %Y %H:%M:%S %Z");
    if (iss.fail()) {
        return "";
    }
 
    // 将 tm 结构转换为系统时钟的时间点
    std::chrono::system_clock::time_point tp = std::chrono::system_clock::from_time_t(std::mktime(&t));
 
    // 将时间点转换为北京时间
    std::chrono::hours offset(8); // 北京时间偏移量为+8小时
    tp += offset;
 
    // 转换为本地时间
    std::time_t tt = std::chrono::system_clock::to_time_t(tp);
    t = *std::localtime(&tt);
 
    std::ostringstream oss;
    // 格式化日期
    oss << std::put_time(&t, "%m%d%H%M%Y.%S");
    return oss.str();
}
 
int main() {
    // ...
}

// 需要定义的宏，要不然会提示找不到某些函数的定义
#define BUILDING_LIBCURL
//#define HTTP_ONLY
// 依赖库
#pragma comment(lib, "ws2_32.lib")
#pragma comment(lib, "wldap32.lib")
#pragma comment(lib, "libcurld.lib")