I have this code here, but I'm unfamiliar with the syntax.
STACK16_SIZE = 100h
stack16 db STACK16_SIZE dup (?)
I think dup
means we declare a variable of type array, as this is a stack, but I'm not sure. So what does dup
mean in TASM, exactly?
STACK16_SIZE dup (?)
means to duplicate the data in parenthesis by STACK16_SIZE
times. It is equivalent to writing ?, ?, ?, ?,
... (100h times)
The data in parens is "uninitialized data". That is, memory is allocated, but not set to any particular value on load.
Assembly does not provide an array "type". If it does, it is only for debuggers for use when inspecting the data. However, in this code snippet, stack16
is a symbol with an address beginning a memory block of bytes—which is counter-intuitive and potentially a source of a subtle bug. For a CPU stack, it really ought to be defined as 16 bit words (dw
) or 32 bit words (dd
).