convert a DWORD to BYTE[4]

bouli

Hello gurus, I'd like to know how I can convert a DWORD (32 bits) value into a byte array of four bytes (32 bits)? DWORD dwLength=(DWORD) file.GetLength(); BYTE length[4]; length contains the value dwLength as a 4 bytes array. Thanks :) Best regards. There is no spoon.

PJ Arends

for (int i = 3; i >= 0; --i)
{
length[3 - i] = (dwLength & (0xff << (i * 8))) >> (i * 8);
}

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Michael Dunn

DWORD dwLength=(DWORD) file.GetLength();
BYTE length[sizeof(DWORD)];

*(DWORD*) &length[0] = dwLength;

Keep in mind that any code doing anything with the bytes will have to account for the endian type of the CPU. --Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | 1ClickPicGrabber | CP SearchBar v2.0.2 | C++ Forum FAQ Strange things are afoot at the U+004B U+20DD

bouli

Hi, Thanks :) Actually I've found the following way: length[0]=HIBYTE(HIWORD(dwLength)); length[1]=LOBYTE(HIWORD(dwLength)); length[2]=HIBYTE(LOWORD(dwLength)); length[3]=LOBYTE(LOWORD(dwLength)); which also works :) There is no spoon.

Mike_V

Or how about: BYTE *pLength = (BYTE*)dwLength; pLength[0] will equal the low byte (assuming an intel machine) What do you need this for?

Michael Dunn

It works, but not the same way as my code in my earlier post. Yours forces big-endian order. Which isn't wrong per se, it's just something to be aware of. Don't try to write that byte array out to a file and read it back in as a DWORD, for example. --Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | 1ClickPicGrabber | CP SearchBar v2.0.2 | C++ Forum FAQ Strange things are afoot at the U+004B U+20DD

softwero

Hi DWORD dwData=0x65A6;//any value BYTE arrDest[4]; memcpy(arrDest,&dwData,sizeof(DWORD)); :)

Priyank Bolia

I have one more method, but not good. union { DWORD dwNumber; BYTE byArry[4]; } http://www.priyank.in/

David Crow

Priyank Bolia wrote: ...but not good Why? This is the method I've used in years past. I find it easier to read than a bunch of pointers ands casts.

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Priyank Bolia

I just write that thinking that people like it or not. I still use it in imaging programs, where image documents are large size and memory and speed are a constraint. It saves memory and helps out small programmers from the pointers nightmare, and the main point is it will save precious time as compare to for loops and memcpy operations etc. http://www.priyank.in/