bind() get "Invalid argument" error in Linux network programming - c

Question

This is my code
#include "basic.h"
#include "bp_socket.h"
int setup_tcp(char *port)
{
struct sockaddr_in server_addr;
in_port_t server_port;
int sock;
int retval; //return value
if ((server_port = atoi(port)) < 0)
{
server_port = (in_port_t)DEFAULT_PORT;
fprintf(stderr, "Error port: %d in line %d\n", (int)server_port, __LINE__);
//fprintf(stderr, "Use default port: %d\n", DEFAULT_PORT);
}
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock < 0)
{
return sock;
}
retval = listen(sock, 40);
if (retval < 0)
{
return retval;
}
memset(&server_addr, 0, sizeof(struct sockaddr_in));
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
server_addr.sin_port = htons(server_port);
server_addr.sin_family = AF_INET;
retval = bind(sock, (struct sockaddr*)&server_addr, sizeof(server_addr));
if (retval < 0)
{
perror("bind");
return retval;
}
return sock;
}
int main()
{
printf("%d\n", setup_tcp("4558"));
perror("");
return 0;
}
I debug my code, then I found bind() return -1
I google it and read man page, but I couldn't found my answer.
function setup_tcp is create socket, and bind with address.
then return a socket or errno value.
How to solve it. I had read my code for many times.
Thank you!

Answer 1

You should move the listen after the bind.
bind returns an error if the socket is already bound, and listen on an unbound socket automatically binds it to a random port number.