如何用c++实现发送邮箱验证码，并写出来代码

实现发送邮箱验证码的具体方法有很多，可以使用第三方库，也可以使用 SMTP 协议来实现。下面给出一个使用 C 语言通过 SMTP 协议实现发送邮箱验证码的示例代码：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define PORT 25
#define SERVER "smtp.qq.com"
#define FROM "from_email@qq.com"
#define TO "to_email@qq.com"
#define USERNAME "from_email@qq.com"
#define PASSWORD "email_password"

int send_email(char *server, int port, char *username, char *password, char *from, char *to, char *subject, char *message) {
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == -1) {
        perror("socket");
        return -1;
    }

    struct sockaddr_in server_address;
    memset(&server_address, 0, sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(port);
    server_address.sin_addr.s_addr = inet_addr(server);

    if (connect(sock, (struct sockaddr*)&server_address, sizeof(server_address)) < 0) {
        perror("connect");
        return -1;
    }

    char recv_buf[1024];
    memset(recv_buf, 0, sizeof(recv_buf));
    int recv_len = recv(sock, recv_buf, sizeof(recv_buf), 0);
    if (recv_len < 0) {
        perror("recv");
        return -1;
    }

    printf("%s", recv_buf);

    char send_buf[1024];
    memset(send_buf, 0, sizeof(send_buf));
    sprintf(send_buf, "HELO %s\r\n", server);
    if (send(sock, send_buf, strlen(send_buf), 0) < 0) {
        perror("send");
        return -1;
    }
    memset(recv_buf, 0, sizeof(recv_buf));
    recv_len = recv(sock, recv_buf, sizeof(recv_buf), 0);
    if (recv_len < 0) {
        perror("recv");
        return -1;