Pointers in Tag Property
lazarus / 31-LCL

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JimKueneman · 2013-03-24 16:56

In Delphi I would create a class or structure and store a pointer to
it in the Tag property of components.  With the cross platform when I
cast pointers to integers I get "not portable" messages. 

What is the correct cross platform way to store a pointer to a class
or structure in a LCL component?

Thanks,
Jim

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JuhaManninen · 2013-03-24 17:24

Quote from: JimKueneman on March 24, 2013, 05:56:42 pmIn Delphi I
would create a class or structure and store a pointer to it in the Tag
property of components.  With the cross platform when I cast pointers
to integers I get "not portable" messages. 

Use PtrInt instead of Integer.

Juha

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howardpc · 2013-03-24 22:30

For casting pointers would it not be safer to use PtrUInt?

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taazz · 2013-03-24 22:34

it doesn't make any difference what so ever other than how the
compiler will interpret the data in memory when asked to print them.
Casting is the action to ask the compiler to handle a piece of memory
in as a certain type it does not convert the data in the memory to the
type requested.

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Leledumbo · 2013-03-25 03:01

QuoteFor casting pointers would it not be safer to use
PtrUInt?Depending on the operation. Tag property is an Integer
(signed), so it's better to use PtrInt. But if the operation is some
kind of pointer arithmetic (manipulated as integer) then PtrUInt is
correct (otherwise you might get negative address).

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PascalDragon · 2013-03-25 16:20

Quote from: Leledumbo on March 25, 2013, 04:01:34 amTag property is an
Integer (signed), so it's better to use PtrInt.
The first part of that statement is not entirely correct. "Tag" is
declared as a "PtrInt" since November 2010, so the signed part is
true, but the Integer part only on 32-bit systems. 

Regards,
Sven

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Leledumbo · 2013-03-25 17:38

QuoteThe first part of that statement is not entirely correct. "Tag"
is declared as a "PtrInt" since November 2010OK, I really really
seldom touched that property actually