Searches the protocols table until a matching protocol number is
    found or until the end of the table is encountered.
    Format
      #include  <netdb.h>
      struct protoent *getprotobynumber  ( int *proto ) ;

1  –  Argument

 proto
    A pointer to a string containing the desired protocol number.

2  –  Description

    This function returns a pointer to a protoent structure
    containing the data from the protocols table. For information
    about the protoent structure, refer to protoent Structure.
    All information is contained in a static area, so it must be
    copied to be saved.
    Related Functions
    See also getprotoent() and getprotobyname().

3  –  Return Values

    NULL               Indicates end of table or an error.
    x                  A pointer to a protoent structure.