Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Sven Barth via fpc-pascal]

Am 10.09.2022 um 01:41 schrieb James Richters:

I thought I would make my own IncArray() function:
Procedure IncArray(Var TheArray);
Begin
SetLength(TheArray,Length(TheArray)+1);
End;

But I get a 'Type Mismatch'  Any ideas how this could be done?  Is this even 
possible without specifying the exact type of array?


You can't simply use a formal parameter for that as SetLength requires 
information about the type which is missing in that case. What you can 
do is use a generic procedure:


=== code begin ===

generic procedure IncArray(var aArray: specialize TArray);
begin
  SetLength(aArray, Length(aArray) + 1);
end;

var
  arr: array of LongInt;
begin
  arr := [1, 2, 3];
  specialize IncArray(arr);
end.

=== code end ===

In 3.3.1 you can also enable the modeswitch 
ImplicitFunctionSpecialization and you can then simply use the following 
as the compiler is able to derive the type to specialize with:


=== code begin ===

IncArray(arr);

=== code end ===

Regards,
Sven
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[James Richters via fpc-pascal]

>With FPC 3.2.0 and newer you can do "Concat(MyArray, [TheNewElement])" or (if 
>modeswitch ArrayOperators is active) "MyArray := MyArray + [TheNewElement]".

I have a lot of arrays of records, but I just build the record into the array 
elements, like this:
  
SetLength(MathArray,Length(MathArray)+1);
  
MathArray[High(MathArray)].Variable:=NewVariable;
  
MathArray[High(MathArray)].Formula:=NewEquation;

Could either of the methods mentioned work directly with something like this or 
would I have to build the record first and do:
MyRecord.Variable:=NewVariable;
MyRecord.Formula:=NewEquation;
MathArray:= MathArray+ MyRecord;


I thought I would make my own IncArray() function:

Procedure IncArray(Var TheArray);
Begin
   SetLength(TheArray,Length(TheArray)+1);
End;

But I get a 'Type Mismatch'  Any ideas how this could be done?  Is this even 
possible without specifying the exact type of array?

James

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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Sven Barth via fpc-pascal]

Luca Olivetti via fpc-pascal  schrieb am
Fr., 9. Sep. 2022, 15:29:

> I don't know if it is more or less efficient than using a dynamic array
> but I think it's nicer.
>

It internally uses a dynamic array as well, but duplicates the size with
each growth and keeps track of a separate count of elements, thus resulting
in a better performance.

Regards,
Sven

>
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Sven Barth via fpc-pascal]

James Richters via fpc-pascal  schrieb am
Fr., 9. Sep. 2022, 14:58:

> I still end up with a lot of
> SetLength(MyArray,Length(MyArray)+1);
> Every time I want to add one more thing to the array.
>

With FPC 3.2.0 and newer you can do "Concat(MyArray, [TheNewElement])" or
(if modeswitch ArrayOperators is active) "MyArray := MyArray +
[TheNewElement]".

Regards,
Sven

>
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Luca Olivetti via fpc-pascal]

El 9/9/22 a les 14:58, James Richters via fpc-pascal ha escrit:


Is there some nifty way to increase a dynamic array by 1 that is more
elegant?
Inc(MyArray); would sure be nice



If I know that I have to regularly add a single element to an array, 
instead of using a dynamic array I just use a TFPGList (if the elements 
are simple types or records) or a TFPGObjectList (if the element are 
objects and I want automatic housekeeping) from the fgl unit, then I can 
just do MyList.Add(element).


I don't know if it is more or less efficient than using a dynamic array 
but I think it's nicer.


There are other generic classes that may be more efficient than fgl but 
I'm just used to fgl.


Bye
--
Luca
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[James Richters via fpc-pascal]

I only recently learned about using Low() and High() and it is so much nicer
than 
For I:= 0 to Length(MyArray)-1 Do

That I actually went though all my code replacing the Length() - 1's with
High()

I still end up with a lot of 
SetLength(MyArray,Length(MyArray)+1); 
Every time I want to add one more thing to the array.

Almost all of my  dynamic arrays do this, because I can only add one thing
at a time to the array... and the reason I wanted it to be dynamic in the
first place.  

Is there some nifty way to increase a dynamic array by 1 that is more
elegant?  
Inc(MyArray); would sure be nice

James


>To avoid this kind of error you can use
>
>   for i:= 0 to High(Rails) do
>
>or even
>
>for i:= Low(Rails) to High(Rails) do

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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Luca Olivetti via fpc-pascal]

El 8/9/22 a les 16:53, Anthony Walter via fpc-pascal ha escrit:

 > curious minds want to know: what was the fix?

In a separate part of the pool table initialization, I was 
precalculating the midpoints and normals for bumper rails. I had 
carelessly written this code:


   for I := 0 to Length(Rails) do
     RailInit(Rails[I], I);


To avoid this kind of error you can use

   for i:= 0 to High(Rails) do

or even

   for i:= Low(Rails) to High(Rails) do

Bye
--
Luca

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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Adriaan van Os via fpc-pascal]

Peter B via fpc-pascal wrote:
I suggest trying without optimisations and/or using cmem, to see if that 
changes the outcome.


I would rather use a system memory debugger  to find the cause 
of the corruption.


Regards,

Adriaan van Os
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Anthony Walter via fpc-pascal]

> curious minds want to know: what was the fix?

In a separate part of the pool table initialization, I was precalculating
the midpoints and normals for bumper rails. I had carelessly written this
code:

  for I := 0 to Length(Rails) do
RailInit(Rails[I], I);
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[wkitty42--- via fpc-pascal]

On 9/8/22 9:54 AM, Anthony Walter via fpc-pascal wrote:

Please ignore this post. I fixed the issue.


curious minds want to know: what was the fix?


--
 NOTE: No off-list assistance is given without prior approval.
   *Please keep mailing list traffic on the list where it belongs!*
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Anthony Walter via fpc-pascal]

Please ignore this post. I fixed the issue.
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Peter B via fpc-pascal]

I suggest trying without optimisations and/or using cmem, to see if that 
changes the outcome.

Also, if the array is corrupted prior to the setlength, then iterating the 
array with a trivial
  with... Writeln(Color)
or whatever, should trigger an exception.

That could then be used at various parts of the program to identify the point 
of corruption,
which might seem unrelated to array in question if the heap is getting messed 
up somehow.


Cheers,
Peter

P.S.

I had a strange (possible) heap corruption issue with a large program a year 
ago that broke stringlists.
I never found the cause, and after many minor code changes, the problem just 
dissappeared.
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Re: [fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Jonas Maebe via fpc-pascal]

On 2022-09-08 09:30, Anthony Walter via fpc-pascal wrote:

Is there a known edge case issue connected to setting the length of 
dynamic arrays?


No, and the location where you're getting the crash suggests an issue in 
your program that has corrupted the heap manager state.



Jonas
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[fpc-pascal] Access Violation When SetLength(DynArray, Value)

[Anthony Walter via fpc-pascal]

Is there a known edge case issue connected to setting the length
of dynamic arrays?

I have a program that simulates a billiards game, and during the rerack
balls method of TPoolTable the number of pool balls on the table varies
based on the rerack option used. Currently, I am having a problem where an
exception is thrown if I try to SetLenth(Balls, 10) or greater than 10.
Values less than 10 work fine, but at 10 balls and above an exception is
thrown right at the SetLength call.

External: SIGSEGV

0041DCA4 eb12 jmp0x41dcb8

0041DCA6 4c89f0   mov%r14,%rax
0041DCA9 488b5008 mov0x8(%rax),%rdx
0041DCAD 488b4018 mov0x18(%rax),%rax
0041DCB1 488982a800   mov%rax,0xa8(%rdx)
^ instruction pointer is at this line ^

I tried compiler both FPC 3.3.1 from trunk source and 3.2.2 from the
official Sourceforge binary.  The same error occurs when building with both
compilers. My platform is x86_64 Linux.

For reference here is the type of Balls:

  TVec2 = record
 X, Y: Single;
  end;

  TPoolBall = record
Pos: TVec2;
Dir: TVec2;
Speed: Double;
Color: LongWord;
Touched: Boolean;
Sinking: Single;
SinkPocket: Integer;
SinkPos: TVec2;
Pocketed: Boolean;
Index: Integer;
  end;

  TPoolBalls = array of TPoolBall;

... later inside TPoolTable ...

  Balls: TPoolBalls;
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