C绑定到指定的TCP端口

Question

i have created a Linux network app with C and it kind of works

except that it every time i run it , it binds to a new Random port

//Create Socket
int socket_desc;
socket_desc=socket(AF_INET,SOCK_STREAM,0);
if (socket_desc==-1)
  perror("Create socket");
struct sockaddr_in address;
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
//Port defined Here:
address.sin_port=htons(81);
//Bind
bind(socket_desc,(struct sockaddr *)&address,sizeof(address));
listen(socket_desc,32);
//Do other stuff (includes accepting connections)

as you can see i have specified port but it still chooses a free Random port

any help or link to a good tutorial on this is appreciated

Answer 1

您需要使用大于1024的端口号。小于1024的端口号是保留端口，由标准服务使用。

Answer 2

There are two reasons of this behaviour (when you specify port, but system binds socket to a random one):

1. If you ask for port below 1024. This is certainly your case
2. If you forgot to use htons() function. In this case bytes of port number are used in wrong order and that leads to #1.