c++ 实现 https

要使用C++实现HTTPS，你需要使用SSL/TLS协议来建立安全连接。下面是一个简单的示例代码，可以用于建立HTTPS连接并发送GET请求：

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

using namespace std;

void print_error(const char* msg) {
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        cerr << "usage: " << argv[0] << " <url>" << endl;
        return 1;
    }
    string url = argv[1];

    // 解析URL
    string host, path;
    int port;
    if (url.substr(0, 8) == "https://") {
        port = 443;
        url = url.substr(8);
    } else {
        cerr << "error: unsupported protocol" << endl;
        return 1;
    }
    size_t pos = url.find('/');
    if (pos == string::npos) {
        host = url;
        path = "/";
    } else {
        host = url.substr(0, pos);
        path = url.substr(pos);
    }

    // 建立TCP连接
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        print_error("socket");
    }
    struct hostent* server = gethostbyname(host.c_str());
    if (server == NULL) {
        cerr << "error: no such host" << endl;
        return 1;
    }
    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    memcpy(&addr.sin_addr.s_addr, server->h_addr, server->h_length);
    if (connect(sockfd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        print_error("connect");
    }

    // 初始化SSL
    SSL_library_init();
    SSL_CTX* ssl_ctx = SSL_CTX_new(TLSv1_2_client_method());
    if (ssl_ctx == NULL) {
        cerr << "error: failed to create SSL_CTX" << endl;
        return 1;
    }
    SSL* ssl = SSL_new(ssl_ctx);
    if (ssl == NULL) {
        cerr << "error: failed to create SSL" << endl;
        return 1;
    }
    if (SSL_set_fd(ssl, sockfd) == 0) {
        cerr << "error: failed to set SSL socket" << endl;
        return 1;
    }
    if (SSL_connect(ssl) != 1) {
        cerr << "error: failed to establish SSL connection" << endl;
        return 1;
    }

    // 发送HTTP请求
    stringstream ss;
    ss << "GET " << path << " HTTP/1.1\r\n";
    ss << "Host: " << host << "\r\n";
    ss << "Connection: close\r\n";
    ss << "\r\n";
    string request = ss.str();
    if (SSL_write(ssl, request.c_str(), request.size()) <= 0) {
        cerr << "error: failed to send HTTP request" << endl;
        return 1;
    }

    // 读取HTTP响应
    char buf[1024];
    int len;
    while ((len = SSL_read(ssl, buf, sizeof(buf))) > 0) {
        fwrite(buf, 1, len, stdout);
    }
    if (len < 0) {
        cerr << "error: failed to read HTTP response" << endl;
        return 1;
    }

    // 关闭SSL和TCP连接
    SSL_shutdown(ssl);
    SSL_free(ssl);
    SSL_CTX_free(ssl_ctx);
    close(sockfd);

    return 0;
}

需要注意的是，在编译时要链接OpenSSL库，例如：

g++ -o https https.cpp -lssl -lcrypto