Address family not supported by protocol

Question

The following code is a socket programming sample for a TCP client.

But when I run this, connect() is returned as Address family not supported by protocol.

I have heard, this problem will happen if the platform does not support ipv6.

But AF_INET I wrote is ipv4.

Also my server, that is CentOS6.4, is configured within an inet6 addr .

Does anyone know why?

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

int
main(){
    struct sockaddr_in server;
    int sock;
    char buf[32];
    int n;
    sock = socket(AF_INET,SOCK_STREAM,0);
    perror("socket");
    server.sin_family = AF_INET;
    server.sin_port = htons(12345);
    inet_pton(AF_INET,"127.0.0.1",&server,sizeof(server));
    connect(sock,(struct sockaddr *)&server,sizeof(server));
    perror("connect");
    memset(buf,0,sizeof(buf));
    n = read(sock,buf,sizeof(buf));
    perror("read");
    printf("%d,%s\n",n,buf);
    close(sock);
    return 0;
}

Answer 1

The code passes the wrong destination address and wrong number of arguments to inet_pton(). (For the latter the compiler should have warned you about, btw)

This line

 inet_pton(AF_INET, "127.0.0.1", &server, sizeof(server));

should be

 inet_pton(AF_INET, "127.0.0.1", &server.sin_addr);

Verbatim from man inet_pton:

int inet_pton(int af, const char *src, void *dst);

AF_INET

[...] The address is converted to a struct in_addr and copied to dst, which must be sizeof(struct in_addr) (4) bytes (32 bits) long.

---

Not related to the problem, but also an issue, is that read() returns ssize_t not int.

The following lines shall be adjusted:

int n;
[...]
printf("%d, %s\n", n, buf);

to become:

ssize_t n;
[...]
printf("%zd, %s\n", n, buf);