Closes a connection and deletes a socket descriptor.
    The $QIO equivalent is the $DASSGN system service.
    Format
      #include  <unixio.h>
      int close  ( s );

1  –  Argument

 s
    A socket descriptor.

2  –  Description

    This function deletes a descriptor from the per-process object
    reference table. Associated TCP connections close first.
    If a call to connect() fails for a socket in connection mode,
    applications should use close() to deallocate the socket and
    descriptor.
    Related Functions
    See also accept(), socket(),  and write().

3  –  Return Values

    0                  Successful completion.
    -1                 Error; errno is set to indicate the error.

4  –  Errors

    EBADF              The socket descriptor is invalid.
    EINTR              The close() function was interrupted by a
                       signal that was caught.