Question

socket( AF_INET, SOCK_STREAM, IPPROTO_TCP )这个返回值表示什么意义

如题，请例举返回值对应的意义，谢谢
初学，不懂哪里去找资料

Answer 1

RETURN VALUE
On success, a file descriptor for the new socket is returned. On
error, -1 is returned, and errno is set appropriately.

ERRORS
EACCES Permission to create a socket of the specified type and/or pro-
tocol is denied.

EAFNOSUPPORT
The implementation does not support the specified address fam-
ily.

EINVAL Unknown protocol, or protocol family not available.

EINVAL Invalid flags in type.

EMFILE Process file table overflow.

ENFILE The system limit on the total number of open files has been
reached.

ENOBUFS or ENOMEM
Insufficient memory is available. The socket cannot be created
until sufficient resources are freed.

EPROTONOSUPPORT
The protocol type or the specified protocol is not supported
within this domain.

Other errors may be generated by the underlying protocol modules.

例子：

clientfd = socket(AF_INET, SOCK_STREAM, 0);
if (clientfd < 0) {
LOG_RECORD(LOG_ERR, "Create socket error.");
return -1;
}
ret = connect(clientfd, (struct sockaddr *)&host_addr, sizeof(host_addr));

Answer 2

如果成功返回一个SOCKET，
如果失败，返回INVALID_SOCKET（-1)。可以用WSAGetLastError来获取错误号。