Title: How to pointer to variant C caution
I just ran across this in some of my old code and thought I'd share it with you:
Consider the following (simplified code):
function CreateVariantPtr(_Value: variant): pVariant;
begin
GetMem(Result, SizeOf(Variant));
Result^ := _Value;
end;
Seems pretty simple, doesn't it? Anybody who can spot the bug?
I got spurious access violations in the line
Result^ := _Value;
Ok, the reason:
Memory allocated with GetMem is not initialised, so the "Variant" pointed to by
Result contains some random data, for example something that might represent a
variant type which requires some finalisation when the variant is changed,
lets say a variant array of some sort. But this finalisation won't work
because the content is just some random garbage, and sometimes I was lucky
(I mean that!) and got an access violation that allowed me to spot the error.
The fix:
function CreateVariantPtr(_Value: variant): pVariant;
begin
GetMem(Result, SizeOf(Variant));
Initialize(Result^);
Result^ := _Value;
end;
{***********--- deutsch ---***********************}
function CreateVariantPtr(_Value: variant): pVariant;
begin
GetMem(Result, SizeOf(Variant));
Result^ := _Value;
end;
Result^ := _Value;
function CreateVariantPtr(_Value: variant): pVariant;
begin
GetMem(Result, SizeOf(Variant));
Initialize(Result^);
Result^ := _Value;
end;