FreeMem question

[xinyiman]

I own a string in memory allocated by a DLL written in C and assigned to a PChar the ShowMessage () I can see correct values. The only thing I can do is to free the memory area occupied. So I decided to use the passing FreeMem PChar but I SIGSERV returns an error. Does anyone know how to address the problem? 

[JuhaManninen]

You can't free the memory allocated by a DLL. The DLL must do it.

Juha

[xinyiman]

You can't free the memory allocated by a DLL. The DLL must do it.

Juha

Ok, I had thought about but I can not get it, I PChar the revision to a hypothetical function that is called

void LiberaStringa(char * variabile)
{
    free(variabile);
}

But it works!

[JuhaManninen]

void LiberaStringa(char * variabile)
{
    free(variabile);
}

If the function is in the DLL, then it works. Yes. It has a different memory manager and address space than your program.

Juha

[xinyiman]

void LiberaStringa(char * variabile)
{
    free(variabile);
}

If the function is in the DLL, then it works. Yes. It has a different memory manager and address space than your program.

Juha

I can not understand, but does not work, it is a dll that I'm writing with devcpp. And your last message is not clear!

[JuhaManninen]

I can not understand, but does not work, it is a dll that I'm writing with devcpp. And your last message is not clear!

Ok. From the previous message I understood it works.
Anyway, if I understand right, the memory allocated by a DLL must be freed by the same DLL. The memory allocated by your main program must be freed by your main program. You can't mix memory management between them.

Juha

[xinyiman]

Okay and I understand that I do not understand why but goes SIGSERV error when trying to deallocate!

[Ñuño_Martínez]

I don't understand that you understand that you don't understand... Oh, wait!

Seriously, Juha was very clear: Memory allocated by the DLL must be deallocated by the DLL same. Each DLL has it's own memory frame. This is what it is.

[José Mejuto]

I own a string in memory allocated by a DLL written in C and assigned to a PChar the ShowMessage () I can see correct values. The only thing I can do is to free the memory area occupied. So I decided to use the passing FreeMem PChar but I SIGSERV returns an error. Does anyone know how to address the problem? 

Hello,

Most DLLs written in C (in Windows) are being linked against msvcrt.dll which handles the memory management. You can try (if the memory allocated in such strings is high along the program life) to dynamic load that DLL and call the "free" method in this DLL. Load time link could work also, but I think it is better a dynamic approach.

type
  Tmsvcrt_free=procedure (P: pointer);

var
  c_free: Tmsvcrt_free;
begin
  h:=LoadLibrary('msvcrt.dll');
  c_free:=Tmsvcrt_free(GetProcAddress(h,'free'));
end;

c_free(mypcharvar);

I had not tested this, use at your own risk

[Marc]

dlls requiring a string to be freed should export a procedure to do so. Never use your own memory manager for this. The method posted by JoshyFun may work, but in general you shouldn't rely on that.

@xinyiman:
Why do you think you need to free the string ?

[xinyiman]

because I allocated with malloc in dll.

We say that the problem does not exist anymore because I abandoned that way!

[Leledumbo]

Doesn't dll have finalization function? You can free your strings there (of course, you have to maintain the references)

[marcov]

(sidenote: on *nix one can use cmem.free() to deallocate C allocated memory. Beware, using this unit will change your memory manager though)