Access violation at address ... in module

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October 21st, 2012, 05:55 PM

simon_66

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Access violation at address ... in module

got it

October 21st, 2012, 07:02 PM

clivew

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Code:

   user := TUser.Create;

Also FYI:
1. Delphi convention is to name private fields of a class (but not other variables) with an initial "F" not "_".
e.g.
FUsername : String;
FPosts : integer;

2. Delphi will automatically initialize private class fields during object creation.
Strings to empty string.
integers to 0.
booleans to False.

No need to initialize them in the create method unless you want to initialize them to
some other value. But BEWARE this only applies to class fields. All other variables do
need initializing.
e.g. method variables and stand alone procedure and function variables.

Clive

October 22nd, 2012, 05:05 PM

simon_66

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Quote:

Originally Posted by clivew

Code:

   user := TUser.Create;

I just added those on the CTOR for testing, I added this there:

Code:

FXMLDoc := TXMLDocument.Create(nil);

Now when I get here it crashes

Code:

XMLNode := FXMLDoc.Node.ChildNodes['user'];

XMLNode is a IXMLNode and FXMLDoc is a TXMLDocument

My error is

Code:

Project2.exe raised exception class EInvalidPointer with message 'Invalid pointer operation'.

My guess is that I need to initialize XMLNode or is it something else?

October 22nd, 2012, 06:19 PM

clivew

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I have not done any testing but I think the code is more like:

Code:

XMLNode := FXMLDoc.ChildNodes,FindNode('user');

Remember, ChildNodes only contains the immediate child nodes of FXMLDoc and FindNode
only looks through the nodes at that level.

You also always need to remember that if FindNode fails then XMLNode will be nil.

Clive

October 22nd, 2012, 06:39 PM

simon_66

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Quote:

Originally Posted by clivew

I have not done any testing but I think the code is more like:

Code:

XMLNode := FXMLDoc.ChildNodes,FindNode('user');

Nope, still crashes, same error.

I tried this code using a TXMLDocument from the tool palette. It works fine, since I'm writing these in a function I don't have access to it.

=================UPDATE==============

The problem is that I had FXMLDoc as a TXMLDocument and not an IXMLDocument.

October 22nd, 2012, 07:14 PM

clivew

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You probably need to post something more comprehensive for us to help further.
(Someone smarter than me might still help).

From the snippets you post, I, myself, can not see where the invalid pointer operation is raised.

Clive

October 22nd, 2012, 08:09 PM

simon_66

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Quote:

Originally Posted by clivew

I wrote this

Code:

Now when I get here it crashes

Code:
XMLNode := FXMLDoc.Node.ChildNodes['user'];


XMLNode is a IXMLNode and FXMLDoc is a TXMLDocument

My error is

Code:
Project2.exe raised exception class EInvalidPointer with message 'Invalid pointer o

I said the Error was caused here and what it said, and the type of the variables.

Not sure how much more I could have posted.

Also, I forgot to say thanks for your help!

October 22nd, 2012, 11:16 PM

clivew

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Nice of you to say thanks - especially as I did not provide a complete answer.
The problem might originate somewhere else and only surface here.

I have similar code (but using the syntax I substituted earlier) that works fine for me.

You could try breaking the code into pieces to see exactly where the error shows itself.

Code:


var
  nodesList: IXMLNodeList;
begin
    XMLNode := FXMLDoc.DocumentElement;
    nodesList := XMLNode.ChildNodes;
    XMLNode :=  nodesList.FindNode('user');
end;

Clive

Access violation at address ... in module

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