Re: Lives there a boolean integer?

Subject: Re: Lives there a boolean integer?
From: "Sandy Harris" <sharris -at- dkl -dot- com>
To: TECHWR-L <techwr-l -at- lists -dot- raycomm -dot- com>
Date: Mon, 06 Mar 2000 14:21:02 -0500

"Mark L. Levinson" wrote:
>
> I'd like to hear from people who are familiar with
> C and with Perl.

I know C well, but don't use Perl.

> I'm documenting a number of functions
> that return the integer 1 to indicate success and the
> integer 0 to indicate failure. Because these are the
> only two values ever returned, I'm being encouraged
> to refer to them as boolean values, and I'm
> being told that there's no real confusion involved
> because neither C nor Perl supports a true boolean
> data type.

C doesn't, not in the sense that Pascal or other more strongly
typed languages do.

> Should I stand on the principle that an integer
> is not boolean?

I'd use the term Boolean, but be quite careful with it.

If your function returns are being used in C flow control contexts:

if( myfunction() )
....
else
....
or
while( myfunction() )
or
for( i = 0 ; myfunction() ; i++ )

Then zero is treated as false and /any non-0 value/ is true. You can
combine these with Boolean operators, ! for not, && for AND, || for OR.
eg. with:

if( functionA() || functionB() )
x = 1 ;
else
x = 2 ;

x is set to one if either function returns non-zero.
(And functionB() isn't even called if A returns non-zero, but that's
off-topic.)

That's one type of Boolean operator in C, but there's another and it
is very different.

C also has bitwise Boolean operations: ^, &, | and ~ for XOR, AND, OR
and NOT respectively, which operate on individual bits of an integer's
binary represenation. so, with four-bit integers, if:

a = 1001
b = 1100
then
~a = 0110
~b = 0011
a&b = 1000
a|b = 1101
a^b = 0101

As long as you carefully avoid confusing the two classes of Boolean
operations (use the word "bitwise" whenever you talk about the 2nd!),
you should be fine.




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