Hi, I'm having a problem with the following code:

  Fstr:=TFileStream.Create('data',fmOpenRead);
  i:=0;
  while i<Fstr.Size do
  begin
    b:=Fstr.ReadByte;
    inc(i);
   ............. Stuff ......................
  end;
  Fstr.Free;  <-- Exception raised here

Do TFileStream objects not have to be freed?

Lazarus version: v0.9.27 r i386-win32-win32/win64
Date 2009-03-19
FPC Version 2.2.2

Hello General,

Tuesday, April 14, 2009, 3:16:13 PM, you wrote:

DC>   Fstr:=TFileStream.Create('data',fmOpenRead);
DC>   i:=0;
DC>   while i<Fstr.Size do
DC>   begin
DC>     b:=Fstr.ReadByte;
DC>     inc(i);
DC>    ............. Stuff ......................
DC>   end;
DC>   Fstr.Free;  <-- Exception raised here

DC> Do TFileStream objects not have to be freed?

Quite sure you are trashing the stack in the "....stuff...." part, maybe an array access ? Pointers ? Do you have range checking enabled ?

In the other hand, use of a TFileStream to read byte by byte is overkill.

did you close Fstr after the while loop? the above doesn't show it...

Dave Coventry wrote

... Do TFileStream objects not have to be freed?

TFileStream's have to be freed. Your problem is most probably caused by memory
corruption somewhere in the skipped part of code. Once the heap is corrupt, any operation that involves allocating or freeing memory may end up with a random fault (but most often, with a SIGSEGV).

Regards,
Sergei

Hi JoshyFun,

Thanks for taking the time.

2009/4/14 JoshyFun :

Quite sure you are trashing the stack in the "....stuff...." part, maybe an array access ? Pointers ? Do you have range checking enabled

Could be, but I'm just adding items to a dynamic array.

In the other hand, use of a TFileStream to read byte by byte is overkill.

True, but I'm going through the file looking for a particular character $1B and assigning data to different dynamic arrays based on the byte following the <ESC> byte.

2009/4/14 Sergei Gorelkin :

Okay, thanks, I'll have a look at that section of the code then.

Thanks for all the suggestions.

It was indeed nothing to do with the code I'd posted but had to do
with a subroutine which added elements to a dynamic array.

I rewrote the subroutine and it now works fine.

2009/4/14 waldo kitty :

Hello Dave,

you wrote

> In the other hand, use of a TFileStream to read byte by byte is > overkill.

DC> True, but I'm going through the file looking for a particular DC> character $1B and assigning data to different dynamic arrays based on DC> the byte following the <ESC> byte.

Anyway, use some kind of cache, each read operation involves a complete read from disk (disk cache mostly) and a transition between user mode to kernel mode and viceversa. Using a simple 4 Kb cache will raise the performance 100 or 1000 times.