I have something like this:

PStruct = ^Struct;
Struct = record
          num    : integer;
          end;

I have a unit to handle that structure ( is a bit more complicated, but is a good example), in this unit I have a procedure that deletes ( disposes ) the pointer. How can I know if a pointer are created or not?, I mean, I don't wont to try to delete something that has not been created yet, but I don't know how to do it, if that is possible.

Thanks a lot.

Zaka.

You can assign "nil" to the pointer before using it, then check if PStruct = nil it wasn't created.

Leonardo.

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Maybe I haven't explain it correctly. What I want is to construct a Unit that contains some procedures, one of them is create(var p : PStruct), and other is delete(var p : PStruct).

I don't create anything, the memory is allocated by the create procedure. How can the procedure know if the argument is a pointer already allocated or not?

I hope I've explain good enough.

Thanks.

Zaka.

Leonardo M. Ramé wrote

You can assign "nil" to the pointer before using it, then check if PStruct = nil it wasn't created. Leonardo.

Zaka E-Lab wrote

I don't create anything, the memory is allocated by the create procedure. How can the procedure know if the argument is a pointer already allocated or not?

It cannot know that without help. You have to do such bookkeeping yourself (e.g., as mentioned before, by assigning nil to all pointers when declaring them). That is one of the basic properties of a language with manual memory management.

Jonas

It's possible to give a default initialization value to a defined type? I suppose that it isn't, but it would be to easy to resolve that trouble that way.

Anyway, I appreciate your help and support.

Thanks.

Zaka.

Zaka E-Lab wrote

It's possible to give a default initialization value to a defined type?

No, that is not possible.

Jonas

Except if your pointer is declared as a member of a class (which is always assigned to nil by default)

But that would not work after the pointer was used and then it's memory freed.
So a better way might be:

Always when declaring pointers do it this way:

var p:  ^sometype = nil;

Then in stead of using the freemem, define your own procedure:

procedure myfreemem(var p: pointer);
begin if pnil then begin freemem(p); p:=nil end end;

(I would regard this a Pascal-improvement?)

Hans Mårtensson

Use FreeAndNil() -

http://www.delphibasics.co.uk/RTL.asp?Name=FreeAndNil

Alan Krause

FreeAndNil works only for classes, not for objects/record

Marc

ReAllocMem(p,0);

Mattias

Ah, now I understand why you use them :)

Anyway does it set p:=nil ?

Marc

Yes.

Mattias