问题
I want to know what is the difference between this code and this code in assembly language:
a db 2 dup (1fh)
b dw 1fh,1fh
and I think that the second code is better and I don't know why they make number first.
回答1:
The 2nd line is equivalent to db 1fh, 0, 1fh, 0, because each arg to DW is a word-sized integer. (And x86 is little-endian)
The 1st line is equivalent to db 1fh, 1fh.
To do that with DW, use dw 1f1fh. For a very short constant, that's maybe clearer. For anything more than 2 repeats of 2 bytes, using the dup syntax is probably clearer for other humans to see that it's the same thing multiple times, without having to look carefully to check for differences.
If you're using an assembler which implicitly associates a size with a symbol, it matters whether you use dw or db, so if you want the symbol to be declared as a byte "variable", you need a db 1fh,1fh or a db 2 dup (1fh).
Think of dup as an operator where the left side is the count and the right side is the thing being repeated. Like Python's 'abc' * 3 being equivalent to "abcabcabc", or Perl's 'abc' x 4, except with the order of the operands reversed.
IDK why MASM is designed this way.
NASM syntax is times 2 db 0x1f. The times repeats a whole pseudo-instruction, or a whole instruction like times 3 imul eax, ecx.
来源：https://stackoverflow.com/questions/52398258/what-is-the-difference-beetwen-dw-and-db-with-dup-in-assembly