Range Check Error and Delphi 7.0

Question

After spending a week checking and fixing my program for memory leaks through FastMM4, I finally test ran my program on a different PC. Now, I am getting "Range Check Error." I have spent hours researching online about this, but none of them seem to give me what I am looking for. My program was complied with the Runtime Error option Range Check. So, I know that's why I am getting the error, but I needed to know exactly why the error is raised.

The program was compiled on XP with Delphi 7.0. The testing PC is a Windows 7. As soon as it starts up, my program begins to communicate through serial port and then followed by "Range Check Error" message boxes. When I stop the serial communication, there are no "Range Check Error" boxes. What does this mean and how do I go about resolving it? I am looking for simple strategy. I know I could spend days checking line by line.

"Range Check Error" caused by improper assignment of values or accessing inaccessible index of an array. Am I correct?

Answer 1

Your understanding of range check errors is correct. They arise when you access an array outside it's bounds. For example:

type
  TFixedArray = array [0..41] of Integer;
var
  a: TFixedArray;
begin
  a[42] := 1+2;//!! this is a range check error !!
end;

Or for a dynamic array:

var
  a: array of Integer;
begin
  SetLength(a, 666);
  a[665] := 12;//this is fine
  a[666] := 42;//!! this is a range check error !!
end;

I've illustrated this with assignment, but reading an array with an index out of bounds will also produce a range error.

The range error should report an address at which it occurs which you can then translate into a code location with your map file. Even better would be if you were using madExcept or some such tool.

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UPDATE

Prompted by Ken, the documentation states what is affected by the range checking option as follows:

In the {$R+} state, all array and string-indexing expressions are verified as being within the defined bounds, and all assignments to scalar and subrange variables are checked to be within range.

Answer 2

Having read other information about the concept of "range check error", I believe that the reason for causing the "range check error" in this scenerio is that: the variable assigning to access the serial port the program reads is an 16-bytes(or smaller) type, and the serial port the program reads exceeds the limitation of the variable. Notice that [When I stop the serial communication, there are no "Range Check Error" boxes.], this should make all things clear.