Quick question with DUP(xx, xx, xx)

[gwapo]

I used to declare an array like this:

  TheData db 128 dup(?) ; array of 128 bytes

But while reading some old drawing software, I've seen a declaration like this:

  CMYKProfile db 1024 dup(0ffh, 0feh, 078h)

I don't know what that declaration means, and MSDN doesn't seem to have
answer either. Probably some of the gurus here can shead a light about
what that data declaration means?

  1. Is it a 3x1024 array initialized with sequence 0ffh, 0feh, 078h?
  2. Or just 1024 bytes array filled with 0ffh, 0feh, 078h?

Thanks,

-chris

[hutch--]

Chris,

MASM never builds complex arrays, you get the byte count with the specified content. Its much the same technique as an array of structures.

[MichaelW]

To expand the answer to a picture, if I place the statement:

CMYKProfile db 1024 dup(0ffh, 0feh, 078h)

In the initialized data section, then assemble, link, and dump the contents of the EXE, this is what the data looks like:

Code Select Expand


00000800  FF FE 78 FF FE 78 FF FE - 78 FF FE 78 FF FE 78 FF  ..x..x..x..x..x.
00000810  FE 78 FF FE 78 FF FE 78 - FF FE 78 FF FE 78 FF FE  .x..x..x..x..x..
. . .
000013E0  FE 78 FF FE 78 FF FE 78 - FF FE 78 FF FE 78 FF FE  .x..x..x..x..x..
000013F0  78 FF FE 78 FF FE 78 FF - FE 78 FF FE 78 FF FE 78  x..x..x..x..x..x


[dsouza123]

Code Select Expand


aa db 9 dup ('A','B','C')

ABCABCABC



[gwapo]

Thanks for the very helpful responses.

:bg

Cheers,

-chris

[jj2007]

aa db 9 dup ('A','B','C')
ABCABCABC

ABCABCABC is nine chars long, but this is not the output you will get: db 9 means "get the full sequence 9 times", i.e. ABCABCABCABCABCABCABCABCABC

[gwapo]

... aa db 9 dup ('A', 'B', 'C')

db 9 means "get the full sequence 9 times", i.e. ABCABCABCABCABCABCABCABCABC

Thanks, this made it clear.

From the original example:

   CMYKProfile db 1024 dup (0ffh, 0feh, 078h)

I did got a 1024x3 block of initialized memory :U

-chris