Memory over lap problem

KC8DKT

Byte FanRPM[noparse][[/noparse]2], A

· FanRPM[noparse][[/noparse]0] := 1
· FanRPM[noparse][[/noparse]1] := 1
· FanRPM[noparse][[/noparse]2] := 1

Y does the above·spill over into byte 3 "Var A".· I have 8 temp probes that use

repeat·IDX from 0 to 7
· Temp[noparse][[/noparse]IDX] := "Some ADC math"

that is doing the same thing.

There must be some little dumb thing I am missing because I found the attached chart in the Prop manual that skips from Long[noparse][[/noparse]0] to Long[noparse][[/noparse]2] as well.·· Anyone have a·SIMPLE answer for this?· Be gentle,· still new to the Prop,·Spin, and english...

Mike Green

You've declared FanRPM as a 2 byte array, yet are referencing FanRPM[noparse][[/noparse] 2]. This will "spill over" into the next variable (A in this case). You have to declare the array (whether FanRPM or Temp) to be large enough for the largest subscript you will use. Keep in mind that subscripts start at zero, so the array size has to include that (if the largest subscript used is 2, then declare the array as having 3 elements).

Paul Baker

This is commonly refered to as "the off by one error". In languages where the first element uses the index 0 (Spin is one of them), the array is declared with N elements which are adressed as 0,1,2,..,N-2,N-1. The N^th element's index is N-1.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

KC8DKT

Thanks, thought the arrays started at 0. What is the deal with the Long[noparse][[/noparse]0] skip Long[noparse][[/noparse]1] then Long[noparse][[/noparse]2] in the chart thats in the manual?

Post Edited (KC8DKT) : 2/27/2007 8:41:29 PM GMT

Mike Green

Aha! The infamous "typographical error" problem. When something doesn't really make sense, you may be right! You might send an e-mail to Stephanie Lindsay at Parallax about this so it can be corrected in the next edition of the manual.

Paul Baker

That is a typo, thanks for catching it. We will put that in the errata shortly.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

KC8DKT

Thank god, thought I was just missing some thing again...

Graham Stabler

If you are placing memory over your lap you really do have a problem [noparse]:)[/noparse]

Thank you, you've been a wonderful audience

Graham

Jamesx

Graham:

Finally got the joke, after reading it 5 times

Jim C