使用C++和libcurl下载指定的文件
今天使用C++语言，利用libcurl库，下载指定的https中的文件：比如https://www.xxxx.com/xxx/yyy/zzz.pdf```
#include <iostream>
#include <fstream>
#include <curl/curl.h>
// 写入数据的回调函数
size_t WriteData(void* ptr, size_t size, size_t nmemb, std::ofstream* stream)
{
stream->write(static_cast<char*>(ptr), size * nmemb);
return size * nmemb;
}
// 分段下载函数
bool DownloadSegment(const std::string& url, std::ofstream& output, long start, long end)
{
CURL* curl;
CURLcode res;
curl = curl_easy_init();
if (curl) {
// 设置URL
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
// 设置Range头
std::string range = std::to_string(start) + "-" + std::to_string(end);
curl_easy_setopt(curl, CURLOPT_RANGE, range.c_str());
// 设置写入数据的回调函数
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteData);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &output);
// 设置SSL选项
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 1L); // 验证服务器的SSL证书
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 2L); // 验证证书上的主机名
// 执行请求
res = curl_easy_perform(curl);
// 清理
curl_easy_cleanup(curl);
if (res != CURLE_OK) {
std::cerr << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
return false;
}
return true;
}
return false;
}
// 获取文件大小
long GetFileSize(const std::string& url)
{
CURL* curl;
CURLcode res;
double file_size = 0.0;
curl = curl_easy_init();
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_NOBODY, 1L); // 不下载内容
curl_easy_setopt(curl, CURLOPT_HEADER, 1L); // 只获取头部信息
// 设置SSL选项
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 1L); // 验证服务器的SSL证书
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 2L); // 验证证书上的主机名
res = curl_easy_perform(curl);
if (res == CURLE_OK) {
res = curl_easy_getinfo(curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD, &file_size);
if ((res == CURLE_OK) && (file_size > 0.0)) {
curl_easy_cleanup(curl);
return static_cast<long>(file_size);
}
} else {
std::cerr << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
}
curl_easy_cleanup(curl);
}
return -1;
}
int main() {
std::string url = "https://img.linux.net.cn/lfs/LFS-BOOK-7.7-systemd.pdf"; // 替换为实际URL
std::string output_filename = "/home/licks/https_download/LFS-BOOK-7.7-systemd.pdf";
long segment_size = 1024 * 1024; // 1MB
// 获取文件大小
long file_size = GetFileSize(url);
if (file_size == -1) {
std::cerr << "Failed to get file size." << std::endl;
return 1;
}
std::cout << "File size: " << file_size << " bytes" << std::endl;
// 打开输出文件
std::ofstream output(output_filename, std::ios::binary);
if (!output.is_open()) {
std::cerr << "Failed to open output file." << std::endl;
return 1;
}
// 分段下载
for (long start = 0; start < file_size; start += segment_size) {
long end = start + segment_size - 1;
if (end >= file_size) {
end = file_size - 1;
}
std::cout << "Downloading segment: " << start << "-" << end << std::endl;
if (!DownloadSegment(url, output, start, end)) {
std::cerr << "Failed to download segment." << std::endl;
output.close();
return 1;
}
}
// 关闭输出文件
output.close();
std::cout << "Download complete." << std::endl;
return 0;
}
```
使用的是CMake作为代码工程管理手段：
```
cmake_minimum_required(VERSION 3.0)
project(download_https)
set(CMAKE_CXX_STANDARD 11)
add_executable(download_https main.cpp)
target_link_libraries(download_https curl)
``` 你是怎么保证每个分块都被写入到正确的位置的，看上去似乎是没有传入偏移量
-----------
哦哦，多线程也没用上，所以说本质上还是顺序写入了
技术贴一定要顶 liuhuanliuhai 发表于 2024-7-10 09:39
技术贴一定要顶
{:1_919:}，比心：互相学习探讨，共同进步 顶一个顶一个 感谢分享 感谢分享 感谢分享 感谢分享 学习了 很好的参考例子
页:
[1]
2