套接字连接失败

Question

我是套接字编程的初学者，正在阅读 Linux 网络编程书籍。我决定按照书中所示实现客户端-服务器连接。服务器程序在 Ubuntu 14.04 机器上运行，客户端代码在 Mac 机器上运行。服务器代码如下

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>

const char message[] = "hello, world\n";

int main()
{
  int sock = 0;
  int port = 0;
  sock = socket(AF_INET, SOCK_STREAM, 0);

  if (sock == -1)
    fprintf(stderr, "failed\n");
  else
    printf("connection is establisshed\n");

  struct sockaddr_in server;
  server.sin_family = AF_INET;
  server.sin_addr.s_addr = htonl(INADDR_ANY );
  server.sin_port = 3500;

  int status = bind(sock, (struct sockaddr*) &server, sizeof(server));
  if (status == 0)
    printf("connection completed\n");
  else
    printf("problem is encountered\n");

  status = listen(sock, 5);
  if (status == 0)
    printf("app is ready to work\n");
  else
  {
    printf("connection is failed\n");
    return 0;
  }

  while (1)
  {
    struct sockaddr_in client = { 0 };
    int sclient = 0;
    int len = sizeof(client);
    int childSocket = accept(sock, (struct sockaddr*) &client, &len);
    if (childSocket == -1)
    {
      printf("cannot accept connection\n");
      close(sock);
      break;
    }

    write(childSocket, message, strlen(message));

    close(childSocket);
  }

  return 0;
}

至于客户端我写了以下代码

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>

int main(int argc, char* argv[])
{
  int sock = 0;
  int port = 0;
  struct sockaddr_in servaddr;
  sock = socket(AF_INET, SOCK_STREAM, 0);
  int status = 0;
  char buffer[256] = "";
  if (sock == -1)
  {
    printf("could not establish connection\n");
    exit(1);
  }

  port = 3500;
  servaddr.sin_family = AF_INET;
  servaddr.sin_addr.s_addr = inet_addr(argv[1]);
  servaddr.sin_port = htons(port);
  status = connect(sock, (struct sockaddr*) &servaddr, sizeof(servaddr));
  if (status == 0)
    printf("connection is established successfully\n");
  else
  {
    printf("could not run the app\n");
    exit(1);
  }

  status = read(sock, buffer, sizeof(buffer));
  if (status > 0)
    printf("%d: %s", status, buffer);

  close(sock);

  return 0;
}

为了获取客户端机器的 IP 地址，我从终端运行 ifconfig 并获取 inet_addr 192.168.1.165 值。现在，当我将该地址字符串作为命令行参数传递时，我收到消息表明应用程序未运行消息。据我了解，我得到的地址有问题。那么问题是什么？ 提前致谢

Answer 1

很可能服务器没有侦听您假设的端口，即3500。

要解决此问题，请更改此行：

server.sin_port=3500

成为

server.sin_port = htons(3500);

_{（要监视哪个进程在哪个地址：端口上列出，您可能希望使用netstat 命令行工具。在您的情况下，可能使用选项-a -p -n）}

---

在最近的系统上，accept() 需要一个指向 socklen_t 的指针作为最后一个参数，所以更改这个

int len=sizeof(client);

成为

socklen_t len = sizeof client; /* sizeof is an operator, not a function¨*/