Is it ok to have a boolean field in that uses values 0 for False and -1 for True?

[Michael Brown]

Hi,

Stupid Question:
I have a boolean field in an Access table that uses values 0 for False and -1 for True

Is this normal? Shouldn't it be 0 and 1?

I know this isn't really the right place for a question like this but I really like this site!

Thanks,
- MB

[RuralGuy]

0 and -1 is exactly right!

[Michael Brown]

Thanks Doomguy!

It seemed weird to me because everywhere I looked online made reference to 0 and 1 as the values, couldn't find anything about -1.

[Rabbit]

Here's why. The Access boolean data type is actually 2 bytes. So it is basically an integer. And VBA doesn't have an unsigned version of integers. So in binary, true is "1000000000000000" while false is "0000000000000000". In signed variables, the leftmost bit, signifies the sign. In the case of signed integers, that leftmost 1 means it's a negative number. And the rest of the zeroes means it's the first negative number, ie -1.

In most other implementations, a boolean is a byte with true being "00000001" and false being "00000000".

[RuralGuy]

Actually any non zero value would work for a false in VBA unless you use the Boolean NOT. Then the -1 makes all kinds of sense since the bits are 1's it negates quite nicely.

[Rabbit]

When evaluating true or false that is the case. But when assigning true or false, it's a constant that it assigns.