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
side.
-hpa
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