怎样用C++处理网络文件流 通过HTTP/FTP协议读写文件

#include <iostream>
#include <string>
#include <curl/curl.h>

size_t WriteCallback(void* contents, size_t size, size_t nmemb, void* userp) {
    ((std::string*)userp)->append((char*)contents, size * nmemb);
    return size * nmemb;
}

int main() {
    CURL* curl;
    CURLcode res;
    std::string readBuffer;

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/file.txt");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &readBuffer);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);

        if(res == CURLE_OK) {
            std::cout << readBuffer << std::endl;
        } else {
            std::cerr << "Error: " << curl_easy_strerror(res) << std::endl;
        }
    }
    return 0;
}

size_t WriteToFileCallback(void* ptr, size_t size, size_t nmemb, FILE* stream) {
    size_t written = fwrite(ptr, size, nmemb, stream);
    return written;
}

FILE* fp = fopen("downloaded_file.txt", "wb");
curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);

curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
curl_easy_setopt(curl, CURLOPT_READDATA, fp);