这里是对各种情况解释比较好的链接
ENETUNREACH,ECONNREFUSED ENETUNREACH,ECONNREFUSED
ENOTSOCK ENOTSOCK
EINTR EINTR
EADDRINUSE EADDRINUSE
EADDRNOTAVAIL EADDRNOTAVAIL
EACCES EACCES
EPERM EPERM
EAFNOSUPPORT EAFNOSUPPORT
EBADF,EALREADY EBADF,EALREADY GNU手册
EFAULT EFAULT