Bytes & Offsets

[flatdog]

I have read the post explaining bits, numbers and hexadecimal and have a (very) basic question. If you take the offset for Autopilot altitude lock (07D0) it is documented as 4 bytes (and is therefore a DWORD?). As far as I can gather the offset on holds two values: 0 for off and 1 for on so why does it need 4 bytes or 32 bits to accomplish this. A link to further reading on this subject would be most welcome.

Thank you,

Philip

[Pete Dowson]

I have read the post explaining bits, numbers and hexadecimal and have a (very) basic question. If you take the offset for Autopilot altitude lock (07D0) it is documented as 4 bytes (and is therefore a DWORD?). As far as I can gather the offset on holds two values: 0 for off and 1 for on so why does it need 4 bytes or 32 bits to accomplish this.

It doesn't. A single byte or even a single bit in a byte (along with 7 other switches) would have been more economical on space. But evidently Microsoft felt they had no need to be economical. It is probably a bit faster too to have everything in 32-bit variables when using a 32-bit machine. Also, if you are lazy when writing code in C or C++ (or most others too), then by default variables will take up the word-size specific to the compiler and target machine -- 32-bit compilers will compile "BOOL" (a boolean value, TRUE or FALSE, 1 or 0) into a 32-bit value and 64-bit compilers will use a 64-bit ("QWORD" or quad-word) value.

Regards

Pete