Creates an SP socket with specified domain and protocol. Returns a file descriptor for the newly created socket.
Following domains are defined at the moment:
protocol parameter defines the type of the socket, which in turn determines the exact semantics of the socket. Check manual pages for individual SP protocols to get the list of available socket types.
The newly created socket is initially not associated with any endpoints. In order to establish a message flow at least one endpoint has to be added to the socket using nn_bind(3) or nn_connect(3) function.
Also note that type argument as found in standard socket(2) function is omitted from nn_socket. All the SP sockets are message-based and thus of SOCK_SEQPACKET type.
If the function succeeds file descriptor of the new socket is returned. Otherwise, -1 is returned and errno is set to to one of the values defined below.
Note that file descriptors returned by nn_socket function are not standard file descriptors and will exhibit undefined behaviour when used with system functions. Moreover, it may happen that a system file descriptor and file descriptor of an SP socket will incidentally collide (be equal).
int s = nn_socket (AF_SP, NN_PUB); assert (s >= 0);