如何在服务器客户端程序中使用sendmsg()系统调用？

使用sendmsg()系统调用来发送消息的好处是可以发送多个缓冲区，例如在SOCK_STREAM套接字上发送带有外部传输控制信息的公共消息时，它非常有用。 以下是一个使用sendmsg()的示例程序：

服务器端代码：

#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

int main() 
{
    int socket_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (socket_fd == -1) {
        perror("socket");
        return 1;
    }

    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(12345);
    addr.sin_addr.s_addr = INADDR_ANY;

    if (bind(socket_fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
        perror("bind");
        return 1;
    }

    if (listen(socket_fd, 5) == -1) {
        perror("listen");
        return 1;
    }

    int client_fd = accept(socket_fd, NULL, NULL);
    if (client_fd == -1) {
        perror("accept");
        return 1;
    }

    struct iovec iov[3];
    char data1[] = "Hello, ";
    char data2[] = "world!";
    char data3[] = "\n";
    iov[0].iov_base = data1;
    iov[0].iov_len = strlen(data1);
    iov[1].iov_base = data2;
    iov[1].iov_len = strlen(data2);
    iov[2].iov_base = data3;
    iov[2].iov_len = strlen(data3);

    struct msghdr message;
    memset(&message, 0, sizeof(message));
    message.msg_iov = iov;
    message.msg_iovlen = 3;

    int result = sendmsg(client_fd, &message, 0);
    if (result == -1) {
        perror("sendmsg");
        return 1;
    }

    close(client_fd);
    close