可选命令行参数的默认值

Question

我有一个套接字编程任务来构建客户端/服务器聊天。当我在终端中键入 3 值时，我的代码有效，但问题是我想不出一种方法将它们全部作为可选参数并在下面的任何示例中设置一些默认值，

1. ./Client
2. ./Client username
3. ./Client username portNumber
4. ./Client username portNumber serverAddress

int
main (int argc, char *argv[])
{
    connection_info connection;
    fd_set file_descriptors;

    if (argc =! 4)
      {
          fprintf (stderr, "Usage: %s <IP> <port> <Name>\n", argv[0]);
          exit (1);
      }


         connect_to_server(&connection, argv[1], argv[2], argv[3]);
}

关于默认值，我只需要用户名是“Anynamous”，ip是“localhost”，而端口是3000

Answer 1

我希望用户名是“Anynamous”，ip 是“localhost”，而端口是 3000

为这些默认值设置并在传递了足够多的参数时更改它们。

int main (int argc, char *argv[]) {
  const char *username = "Anynamous"; // Or maybe "Anonymous" 
  const char *ip = "localhost";
  int port = 3000;

  if (argc >= 2) username = argv[1];
  if (argc >= 3) ip = argv[2];
  if (argc >= 4) port = atoi(argv[3]);  // Could add some conversion checking here.

  connection_info connection;
  connect_to_server(&connection, username, ip, port);
  fd_set file_descriptors;
  // ...
}