why does the following code compile perfectly?
Data Segment
Var1 Dw (any 4 digit hex value)
Var2 Dw Var1
Data Ends
what does the line "Var2 Dw Var1" even mean? I thought that only an immediate value can go after the type defining .
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menjaraz
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user1020063
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Which assembler are you using? – BlackBear Oct 29 '11 at 19:25
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TurboShell , similar to TurboAsm – user1020063 Oct 29 '11 at 19:30
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If my memory serves me right (and it might not), it will declare `Var2` to hold the offset of where `Var1` is located inside the segment `Var1` is in. In the specific example of the question, the value of `Var2` would be 0, since `Var1` is the first declaration inside the segment. – Lasse V. Karlsen Oct 29 '11 at 19:34
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Did you test it by declaring more variables before `Var1` and seeing if the value of `Var2` varied, as I said? – Lasse V. Karlsen Oct 29 '11 at 19:38
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yes I did. it is just like you said – user1020063 Oct 29 '11 at 19:41
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Then I'll move my comment to an answer. – Lasse V. Karlsen Oct 29 '11 at 19:42
1 Answers
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When you declare a variable like this:
VARX DW VARY
then you're basically saying:
VAR DW (offset of VARY into the segment VARY is in)
In your specific example, Var1 is the first variable in the data segment, so the declaration of Var2is equivalent to:
Var2 DW 0x0000
If, later on, you add more variables before Var1, in effect moving Var1 further into the segment, the value of Var2 will adjust correspondingly.
The typical usage of this is to get the start of array-like constructs by getting the address (offset in this context) of the start of the array.
Lasse V. Karlsen
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