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pointer

Posted on 1998-04-06
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Last Modified: 2010-04-06
DELPHIer,

How can I get the pointer of a function ?
Why I cannot access the data when the pointer is nil ?

Andrew
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Question by:andrewyu
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extreme earned 10 total points
ID: 1361313
I presume you want to get the address of a function. Well, to get the address depends on the context where you are working. For example, if you want to assign the address of a function to a variable to call the function later using this var you should write code like this:

var
  FOnClick : TNotifyEvent;
begin
  FOnClick := Form1.Button1Click;

  if assigned (FOnClick)
    then FOnClick (xx);


that code get the address of the button1Click method and assign it to the var FOnClick, later you can use the var to call the function, but always you have to check if the value is diferent of nil using assigned. If you don't do so, trying to do something like:

if FOnClick <> nil
   then xxxx....

Delphi tried to call the function because it's in the left of an expression, when the function is in the right in an assignment statement then delphi get the address. That's why you cannot compare directly with nil the function pointer.

When a pointer is nil, is because the pointer don't points to anything, so you cannot reference the pointer otherwise you will get an access violation.
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