[Solved] AccessViolationException in Delphi – impossible (check it, unbelievable…)

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Try changing PBoolean to PBOOL

function(IsEnabled: PBOOL): HRESULT; stdcall;

var
  Flag: BOOL;

PBoolean is a pointer to a Pascal Boolean which is 1 byte in size. PBOOL is a pointer to a Windows (C based) BOOL, which is 4 bytes in size. You need to match the size expected by windows.

In general, when translating Windows API calls to Delphi, use the same named data type as the API. Windows.pas has type definitions mapping these to Delphi types, e.g. type BOOL = LongBool;

Also it is usual (but not required) in Delphi to change pointer parameters to var. A var parameter is Pascal syntactic sugar for pass-by-reference which isn’t available in C.

function(var IsEnabled: BOOL): HRESULT; stdcall;
....
    DwmIsCompositionEnabledFunc(Flag); // no @ operator

NOTE: I can’t test this, as I only have XP available.

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solved AccessViolationException in Delphi – impossible (check it, unbelievable…)