[lkml]   [2002]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: RFC: booleans and the kernel
Followup to:  <>
By author: Oliver Xymoron <>
In newsgroup:
> > It doesn't fix "if ( x = true)". If would
> > just make it more legit to use "if (x)".
> It's been legit and idiomatic since day 1, if not sooner.

The main reasons for bool is:

a) The ability to save space. No need to waste a 32- or 64-bit word
to hold a single bit. If you're on an architecture that has flags
or predicates you may be able to carry a boolean in such a value
instead of in a full register.

b) Compatibility with other languages, including but not limited to
C++ (there is a standard under development for inter-language linking,
incidentally.) C++, of course, needs bool for overloading reasons.

c) The ability to cast to bool and get an unambiguous true or false:

b = (bool)a;

This replaces the idiomatic but occationally confusing

b = !!a;

d) Similarly, you can avoid doing booleanization multiple times:

/* Highly artificial example */
int foo(bool a)
return a ? 55 : 47;

... could be implemented by the compiler as 47 + (a << 3), or
depending on your ABI convention, perhaps a caller calling
foo(x < 4) could be implemented as foo(x-4) without needing to
convert it into an integer of exactly 1 and 0.

Given the way C currently does it, you pretty much have do
booleanize both in the caller and the callee to be on the safe


<> at work, <> in private!
"Unix gives you enough rope to shoot yourself in the foot." <>
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:15    [W:0.189 / U:3.840 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site