Socket API :Socket operation on non-socket

Question

Hello I have a problem when I am writing the server using the socket api. I always get this error: "Socket operation on non-socket"

struct sockaddr_in addr;
int port = 10000;
int sd;

memset((char *) &addr,0, sizeof(addr));
addr.sin_family = PF_INET;
addr.sin_addr.s_addr = htonl(INADDR_ANY);
addr.sin_port = htonl((u_short)port);

if ((sd = socket(PF_INET, SOCK_STREAM, 0) < 0)) {

    printf("socket failed");
}

if(bind(sd, (struct sockaddr *)&addr, sizeof(addr)) != 0)
{
    printf(strerror(errno));
}

close(sd);


return 0;}

If you get an error, (a) don't just print some message of your own devising: use perror() or strerror(), and (b) don't continue as though the error didn't happen. And it isn't correct to test system calls for != 0: the correct test is == -1 or < 0. — user207421
– user207421, Commented Feb 26, 2015 at 23:58

Martin Törnwall · Accepted Answer · 2015-02-26 23:38:25Z

1

The line:

if ((sd = socket(PF_INET, SOCK_STREAM, 0) < 0)) {

Doesn't do what you think. If you look closely at the placement of parentheses (and remember that the < operator has higher priority than =) you will notice that you are actually assigning sd the value of the expression socket(PF_INET, SOCK_STREAM, 0) < 0.

In short, sd will most likely end up containing the value 0, because that's what the above expression would normally evaluate to. This explains the "socket operation on non-socket" error; it really isn't a socket.

So the line should read:

if ((sd = socket(PF_INET, SOCK_STREAM, 0)) < 0) {

Notice how I shifted a closing parenthesis left by two tokens.

answered Feb 26, 2015 at 23:38

Martin Törnwall

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Comments

Stian Skjelstad · Accepted Answer · 2018-05-14 12:08:54Z

0

addr.sin_port = htonl((u_short)port);

should read

addr.sin_port = htons((u_short)port);

since port is 16bit number.

answered May 14, 2018 at 12:08

Stian Skjelstad

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