size of variant records
lazarus / 62-General

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440bx · 2022-01-10 23:54

Hello,

Does FPC provide a way to determine the size of a variant record up to
and including a specific field/variant ?

For instance, in the following sample: Code: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {$APPTYPE
CONSOLE} type  TSOME_VARIANT_TYPE = record    VariantSize          :
DWORD;     SomeField            : qword;     case integer of      1 :
(           a : byte;          );       2 : (           b : word;    
    );       3 : (           c : DWORD;          );       4 : (      
   d : qword;          );  end; var  Size : DWORD; begin   { how to
get the size up to and including field a or b or c ?               }  
{ Size := ???                                                        
     }end.Is there a way to determine the size of the record up to and
including a (but not b, c and d) ? or upto and including b (or c)
excluding the fields that follow it ?

Thank you for your help.

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engkin · 2022-01-11 01:16

Add the offset of the field to the SizeOf the field?

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440bx · 2022-01-11 02:31

Quote from: engkin on January 11, 2022, 02:16:40 amAdd the offset of
the field to the SizeOf the field?
Yes, that will do it.  I was hoping for something like
"SizeTo(<Record.Fieldname>);  Can't have it all, I guess

Thank you for the suggestion.  At least it tells me that there isn't a
really straightforward/direct way of getting the size up to some
field.

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engkin · 2022-01-11 03:21

On a positive note, it is a compile-time value.

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PascalDragon · 2022-01-11 08:28

Quote from: 440bx on January 11, 2022, 03:31:55 amQuote from: engkin
on January 11, 2022, 02:16:40 amAdd the offset of the field to the
SizeOf the field?
Yes, that will do it.  I was hoping for something like
"SizeTo(<Record.Fieldname>);  Can't have it all, I guess

Thank you for the suggestion.  At least it tells me that there isn't a
really straightforward/direct way of getting the size up to some
field.

Well, the size up to some field is the offset of that field

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440bx · 2022-01-11 08:34

Quote from: PascalDragon on January 11, 2022, 09:28:28 amWell, the
size up to some field is the offset of that field
Wouldn't it be the offset to the _next_ field ? (which makes the
expression to calculate the size a bit confusing)

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PascalDragon · 2022-01-11 08:52

Quote from: 440bx on January 11, 2022, 09:34:45 amQuote from:
PascalDragon on January 11, 2022, 09:28:28 amWell, the size up to some
field is the offset of that field
Wouldn't it be the offset to the _next_ field ? (which makes the
expression to calculate the size a bit confusing)

Right, forgot that you meant including the field