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@node Language facilities
@chapter Language facilities
@menu
* Alternative tokens:: Alternative spellings of common operators.
* Booleans:: Proper booleans in the C programming language.
@end menu
@node Alternative tokens
@section Alternative tokens
@hfindex iso646.h
@cpindex Alternative tokens
@cpindex Tokens, alternative
The @sc{ISO}@tie{}C90 standard was amended in 1995 to
include alternative spellings of common operators,
referred to as C alternative tokens.
@table @code
@item and
@fnindex and
@code{&&}
@item and_eq
@fnindex and_eq
@code{&=}
@item bitand
@fnindex bitand
@code{&}
@item bitor
@fnindex bitor
@code{|}
@item compl
@fnindex compl
@code{~}
@item not
@fnindex not
@code{!}
@item not_eq
@fnindex not_eq
@code{!=}
@item or
@fnindex or
@code{||}
@item or_eq
@fnindex or_eq
@code{|=}
@item xor
@fnindex xor
@code{^}
@item xor_eq
@fnindex xor_eq
@code{^=}
@end table
These alternative spellings are implemented as a
group of macro constants, and are made available
by including the header file @file{<iso646.h>}.
They were added because a concern that the standard
names are difficult to type on some keyboard-layouts.
Use of these alternative tokens are discouraged,
they lessen the readability of your code. If it is
difficult to type some characters without yout
keyboard-layout, it is better to change keyboard-layout.
@node Booleans
@section Booleans
@hfindex stdbool.h
@cpindex Booleans
@tpindex bool
@tpindex _Bool
@lvindex true
@lvindex false
@lvindex __bool_true_false_are_defined
The @sc{ISO}@tie{}C99 standard added the keyword
@code{_Bool}, as well as a set macro definitions
that are made available by including the header
file @file{<stdbool.h>}.
@table @code
@item bool
Expands to @code{_Bool}, an integer data
type. Any non-zero value (any true value)
is stored as 1, to avoid integer overflows,
that may occur when using @code{int}, and
not using @code{!!} when casting to @code{int}.
@item true
Has the value 1, and represents a true value.
@item false
Has the value 0, and represents a false value.
@item __bool_true_false_are_defined
Will be defined if the other three macros
are define. So, it will will be defined if
the header file is included.
@end table
The macros @code{bool}, @code{true}, and @code{false}
may be removed and become built-in the future; or at
least, the right to undefined them may be removed.
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