"Freemem" statement now gives "Invalid Pointer Operation". Used to work OK.

Hello Experts... I have a routine which would read a "chunk" of bytes from a file using a stream, do a bit of processing, then write that chunk to an output stream.. and repeat this till nothing left to read. Before the read I have these statements:

    Chunksize := 2048000;
    GetMem(CopyBuffer, ChunkSize); // CopyBuffer is defined as a PChar

And I do the read as such:

ibytesOK:=InfileStream.Read(CopyBuffer^, ChunkSize);

At the end when cleaning things up and closing files, I have this statement:

FreeMem(CopyBuffer, Chunksize);


This all used to work fine, until I just added some code that steps through the CopyBuffer a bit, looking for a #13 character:

while CopyBuffer^ <> #13 do  
       Inc(CopyBuffer);

Now when I run it, it crashes on the FreeMem(CopyBuffer, Chunksize); statement giving "Invalid Pointer Operation". Any idea how to remedy this, anyone?

Thanks!
    Shawn
shawn857Asked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Sinisa VukSoftware architectCommented:
CopyBuffer is a pointer variable - point to some memory block. You must never use it in such operation which can "force" to "point" to somewhere else. This Inc function is one of them. Rather use temporary pointer:

ptr: PChar;
len: Integer;
begin
...
ptr := CopyBuffer; //copy point location
len := 0;
while (ptr^ <> #13) and (len < ChunkSize) do   //chk length too
begin
     Inc(ptr);
     Inc(len);
end;

//use ptr after that....
...

//free mem
ptr := nil;
FreeMem(CopyBuffer);
end;

Open in new window


...always check if pointer location is nor run over....(ChunkSize)
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
shawn857Author Commented:
ahh you are right Sinisa... thank you my friend!

Cheers
   Shawn
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Delphi

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.