OpenEuphoria

Re: multiple pointers [GEN]

• Posted by Derek Parnell <derekp at solace.com.au> Oct 16, 2000
• 625 views

Hi,
I'll have a go at this, but I can't test it on my machine at work.

>//in C
>
>struct hostent {
>  char *h_name;                // official name of host
>  char **h_aliases;    // alias list
>  int h_addrtype;      // host address type
>  int h_length;                // length of address
>  char **h_addr_list;  // list of addresses
>};

-- Assuming that Linux is being used and that 'int' is a 32-bit signed
integer.
constant
  h_name = 0,
  h_aliases = 4,
  h_addrtype = 8,
  h_length = 12,
  h_addr_list = 16

atom hostent_p,
     name_p,
     aliases_p,
     alias_p,
     addr_list_p,
     addr_p,
     addrtype,
     length

      -- Get address of the hostent structure
        hostent_p = get_hostent()

      -- Get the address of the first character in the name.
      name_p = peek4u(hostent_p + h_name)

      -- Get the address of the first alias pointer
      aliases_p = peek4u(hostent_p + h_aliases)

      -- Get the address of the first character in the first alias
      alias_p = peek4u( aliases_p )

      -- Get the '32-bit int' address type
      addrtype = peek4s(hostent_p + h_addrtype)

      -- Get the '32-bit int' length
      length = peek4s(hostent_p + h_length)

      -- Get the address of the first addr in the list
      addr_list_p = peek4u(hostent_p + h_addr_list)

      -- Get the address of the first char in the first addr in the list
      addr_p = peek4u(addr_list_p)

With the name_p address, you can use the earlier reply to convert a C-string
into a Euphoria sequence.

      theName = CstrToSeq(name_p)

With the aliases and the addr_list, you also need to know how many entries
are in these lists. From memory, I think that these lists are terminated by
a zero address. If so you can do something like ...

    -- initialize my alias sequence to empty
    aliases = {}

    -- Copy the Pointer-to-pointer address
    memaddress = aliases_p

    -- collect aliases until I find a zero memory address
    while 1 do

      -- pick up the next pointer to an alias C-string
      alias_p = peek4u( memaddress )
      if alias_p = 0 then
          exit -- Got them all.
      end if

      -- convert to a sequence and add to the my alias list
      aliases = append(aliases, CstrToSeq( alias_p ) )

      -- calculate where the next alias pointer is.
      memaddress += 4

    end while


-----
cheers,
Derek Parnell
derekp at solace.com.au
Solace Limited ( http://www.solace.com.au )
Melbourne, Australia
+61 3 9291 7557