How to Check if its been assigned activated

Hi, I'm having a problem, I'd like to be able to know if the hook is active and filled or empty.
var
MainHook : HHOOK;


//this creates
MainHook := SetWindowsHookEx(WH_JOURNALRECORD, KeyboardHook, hInstance, 0);

//this unhooks
UnhookWindowsHookEx(MainHook);
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eNarcAsked:
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LelikInsideConnect With a Mentor Commented:
if Assigned(MainHook) then...

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Ephraim WangoyaConnect With a Mentor Commented:
Check if it returns zero

MainHook := SetWindowsHookEx(WH_JOURNALRECORD, KeyboardHook, hInstance, 0);
if MainHook > 0 then  //this was successful
  ........
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jimyXConnect With a Mentor Commented:
HHook is of LongWord data type so to know if it is assigned a value you have to reset its default value first then you can match it to what you have set it to otherwise it will be holding a random default value.

You can test the default value this way:
var
  MainHook : HHOOK;
begin
  Showmessage(IntToStr(MainHook));

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As you can see it will not be easy to distinguish if it's assigned that value or it's the default.
The best thing to do is, assign your own default value, let's say ZERO, and at any point if it is holding zero then it has not not assigned a value.
var
  MainHook : HHOOK;
begin
  MainHook := 0;
  //...
  // to check if it's assigned then
  If MainHook = 0 then
    // it is not assigned

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Ephraim WangoyaConnect With a Mentor Commented:

<so to know if it is assigned a value you have to reset its default value first >

No, you don't have to do that

var
   MainHook : HHOOK;
begin
   //the very first statement already assigns a value to it, you don't need to assign a default value
  MainHook := SetWindowsHookEx(WH_JOURNALRECORD, KeyboardHook, hInstance, 0);
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