Address family not supported by protocol

Question

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 he

Answer 1

Set the server address like this;

addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(host);
addr.sin_port = htons(port);

Answer 2

I seen this error during bind. Cause was of using localhost instead of IP:

./myprogram localhost:7777
*** exception! `bind' failed for `localhost:7777' (97, Address family not supported by protocol)

./myprogram 127.0.0.1:7777
OK! Listening...

In addition: this error happens on one Linux host and does not appear on another. I check and compare network settings on this machines (lo device, /etc/hosts, /etc/host.conf, etc) and not found essential difference

Answer 3

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.

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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);