Simple math overflow problem (and var declared as int64 in IDE shows as Int)

[Simon Devlin]

Hi folks,

I've been bashing my head against this all afternoon and am now totally
baffled.

Given this (a simple routine to turn a ip address string into an decimal)

<snip>
Dim Parts(3) as string ' --> each element is an integer in the range 0-255
Dim Big as int64 = 0

Big =16777216 * cint(Parts(0))
Big = big + (65536 * cint(Parts(1)))
big = big + (256 * cint(parts(2)))
big = big + cint(parts(3))

I get arithmetic overflow errors on execution (at the first line).
Interestingly if I play around with constants then by doing

big = 16777216 * 255

The IDE reports "Constant expression not representable in type integer".
This doesn't make a whole lot of sense given that big is declared as an
int64. Values greater than 127 result in the same - clearly suggesting an
overflow somewhere, but these numbers are well within the scope of an int64
(ordinarilly a uint32 is sufficient)

Does anyone have any suggestions to stop me going mad. I'm not that
experienced VB.NET / ASP.NET, so hopefully I'm missing something really
obvious.

Thanks

[Nick Savoiu]

Kevin,

I'm not an expert either but I don't see any 'int64' type for Visual Basic.
Looks like you're just getting an 'Integer' which will overflow after 2**31.
Have you tried "Long"?

Nick

"Simon Devlin" <si**********@7layerforensics.com> wrote in message
news:3f***********************@newscene.com...

Hi folks,

I've been bashing my head against this all afternoon and am now totally
baffled.

Given this (a simple routine to turn a ip address string into an decimal)

<snip>
Dim Parts(3) as string ' --> each element is an integer in the range 0-255 Dim Big as int64 = 0

Big =16777216 * cint(Parts(0))
Big = big + (65536 * cint(Parts(1)))
big = big + (256 * cint(parts(2)))
big = big + cint(parts(3))

I get arithmetic overflow errors on execution (at the first line).
Interestingly if I play around with constants then by doing

big = 16777216 * 255

The IDE reports "Constant expression not representable in type integer".
This doesn't make a whole lot of sense given that big is declared as an
int64. Values greater than 127 result in the same - clearly suggesting an
overflow somewhere, but these numbers are well within the scope of an int64 (ordinarilly a uint32 is sufficient)

Does anyone have any suggestions to stop me going mad. I'm not that
experienced VB.NET / ASP.NET, so hopefully I'm missing something really
obvious.

Thanks

[Kevin Spencer]

Use CLng() instead of CInt().

--
HTH,
Kevin Spencer
..Net Developer
Microsoft MVP
Big things are made up
of lots of little things.

"Simon Devlin" <si**********@7layerforensics.com> wrote in message
news:3f***********************@newscene.com...

Hi folks,

I've been bashing my head against this all afternoon and am now totally
baffled.

Given this (a simple routine to turn a ip address string into an decimal)

<snip>
Dim Parts(3) as string ' --> each element is an integer in the range 0-255 Dim Big as int64 = 0

Big =16777216 * cint(Parts(0))
Big = big + (65536 * cint(Parts(1)))
big = big + (256 * cint(parts(2)))
big = big + cint(parts(3))

I get arithmetic overflow errors on execution (at the first line).
Interestingly if I play around with constants then by doing

big = 16777216 * 255

The IDE reports "Constant expression not representable in type integer".
This doesn't make a whole lot of sense given that big is declared as an
int64. Values greater than 127 result in the same - clearly suggesting an
overflow somewhere, but these numbers are well within the scope of an int64 (ordinarilly a uint32 is sufficient)

Does anyone have any suggestions to stop me going mad. I'm not that
experienced VB.NET / ASP.NET, so hopefully I'm missing something really
obvious.

Thanks

[Kevin Spencer]

int64 is a .Net Data Type, available via C# OR VB.Net, or any other .Net
language.

--
HTH,
Kevin Spencer
..Net Developer
Microsoft MVP
Big things are made up
of lots of little things.

"Nick Savoiu" <savoiu@ics_.uci_.edu_> wrote in message
news:#3**************@tk2msftngp13.phx.gbl...

Kevin,

I'm not an expert either but I don't see any 'int64' type for Visual Basic. Looks like you're just getting an 'Integer' which will overflow after 2**31. Have you tried "Long"?

Nick

"Simon Devlin" <si**********@7layerforensics.com> wrote in message
news:3f***********************@newscene.com...

Hi folks,

I've been bashing my head against this all afternoon and am now totally
baffled.

Given this (a simple routine to turn a ip address string into an decimal)
<snip>
Dim Parts(3) as string ' --> each element is an integer in the range

0-255

Dim Big as int64 = 0

Big =16777216 * cint(Parts(0))
Big = big + (65536 * cint(Parts(1)))
big = big + (256 * cint(parts(2)))
big = big + cint(parts(3))

I get arithmetic overflow errors on execution (at the first line).
Interestingly if I play around with constants then by doing

big = 16777216 * 255

The IDE reports "Constant expression not representable in type integer".
This doesn't make a whole lot of sense given that big is declared as an
int64. Values greater than 127 result in the same - clearly suggesting an overflow somewhere, but these numbers are well within the scope of an

int64

(ordinarilly a uint32 is sufficient)

Does anyone have any suggestions to stop me going mad. I'm not that
experienced VB.NET / ASP.NET, so hopefully I'm missing something really
obvious.

Thanks

[Simon Devlin]

Thanks. That's done the trick, but I don't really understand why. Surely
the parenethesis should mean that the cint conversion should occur first
(and I know that the target of that operation is always a 8 bit value).

I'm also not clear why the constant expression in the IDE errors too.

I'm happy that this has resolved my problem, but it all seems a little odd.

Regards

"Kevin Spencer" <ke***@takempis.com> wrote in message
news:Ok**************@TK2MSFTNGP10.phx.gbl...

Use CLng() instead of CInt().