Calculate the Broadcastaddress

[Marc Giesmann]

Hello, everybody.
Just a little question about broadcasts.

As far as I know, the broadcast-address is just the binary equivalent (EQV) to the subnetmask. But my program always returns "192.168.1.235" as my broadcasr. My (only) IP here is 192.168.1.1, and my subnet is a standard C-subnet: 255.255.255.0

So, whats wrong here?

#COMPILE EXE
#DIM ALL

#INCLUDE "Win32API.inc"
#INCLUDE "iphlpapi.inc"
FUNCTION ip2num (BYVAL sIP AS STRING) AS LONG
      LOCAL ix AS LONG
      LOCAL nResult AS LONG
      LOCAL pb AS BYTE PTR
      pb = VARPTR(nResult) + SIZEOF(nResult) - 1

      FOR ix = 4 TO 1 STEP -1
         @pb = VAL(PARSE$(sIP, ".", ix))
         DECR pb

      NEXT
      FUNCTION = nResult
END FUNCTION

FUNCTION num2ip(BYVAL ip AS LONG) AS STRING
  LOCAL b AS BYTE PTR

  b = VARPTR(ip)
  FUNCTION = FORMAT$(@b[0]) & "." & FORMAT$(@b[1]) & "." & _
             FORMAT$(@b[2]) & "." & FORMAT$(@b[3])
END FUNCTION

'Thanks to Steve Smith and William Burns- > Stolen from
'http://www.powerbasic.com/support/pbforums/showthread.php?t=13418
FUNCTION getSubnet(sIP AS STRING) AS STRING
    LOCAL tbl AS MIB_IPADDRTABLE PTR
    LOCAL Ret AS LONG
    LOCAL a AS LONG
    LOCAL i AS LONG
    LOCAL MyAddr AS STRING
    LOCAL sBuffer AS STRING

    'First, get the size result in Ret
    a = GetIpAddrTable (BYVAL 0, Ret, 0)
    sBuffer = SPACE$(Ret)
    a = GetIpAddrTable (BYVAL STRPTR(sBuffer), Ret, 0)
    tbl = STRPTR(sBuffer)

    FOR i = 0 TO @tbl.dwNumEntries - 1
        MyAddr = num2ip(@tbl.table(i).dwAddr)

        IF MyAddr = sIP THEN
         FUNCTION =  num2ip(@tbl.table(i).dwMask)
         EXIT FUNCTION
        END IF
    NEXT
END FUNCTION

FUNCTION GetSystemIP() AS STRING
   LOCAL ip AS LONG

   HOST ADDR TO ip&
   FUNCTION =  num2ip(ip)
END FUNCTION

FUNCTION GetSystemBroadcast(sIP AS STRING) AS STRING
    'MSGBOX BIN$(ip2num(sIP), 32)    + $CRLF + _
    'BIN$(ip2num(getSubnet(sIP)),32) + $CRLF + _
    'BIN$(ip2num(sIP) EQV ip2num(getSubnet(sIP)),32  )

    FUNCTION = num2ip(( ip2num(GetSystemIP()) EQV ip2num(getSubnet(GetSystemIP()))))
END FUNCTION

FUNCTION PBMAIN()
       MSGBOX "IP:" + GetSystemIP()
       MSGBOX "Subnet: " + getSubnet(GetSystemIP())

       MSGBOX "Broadcast: " + GetSystemBroadcast(GetSystemIP())
END FUNCTION

Feel free to uncomment the MSGBOX to see, If the EQV operator works properly.

Greetings from germany,
Marc

[Marc Giesmann]

Got it now...

Okay, got it now.

Its not EQV what should be used- if you use EQV you just would'nt often reach 255 on the last host-byte.

Heres the working thing:
Broadcast = IP-Adress OR NOT(Subnetmask)

FUNCTION GetSystemBroadcast(sIP AS STRING) AS STRING
   LOCAL lIP, lSUB, lBR AS LONG

   lIP    = ip2num(sIP)
   lSUB = ip2num(getSubNet(sIP))
   lBR = lIP OR NOT(lSUB)

   'MSGBOX BIN$(lIP, 32) + $CRLF + _
'              BIN$(lSUB,32) + $CRLF + _
'              BIN$(lBR,32  )

   FUNCTION = num2ip(lBR)
END FUNCTION

Thanks and bye...
Marc