Boolean Values

[Ian Tuomi]

How can I define a boolean value in c? (an value that can only be either
1 or 0) I feel bad for the memory loss when declaring ints for variables
that do not need that much memory.
--
Ian Tuomi
Jyväskylä, Finland

"Very funny scotty, now beam down my clothes."

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NOTE: Remove NOSPAM from address

[Goran Larsson]

In article <3F************ **@jpl.nasa.gov >,
E. Robert Tisdale <E.************ **@jpl.nasa.gov > wrote:

Don't use the stdbool.h header file.
You have to motivate that recommendation.
If you don't have a stdbool.h header file, you can use
What should I do if I have a stdbool.h file? You just told us
not to use it.
#ifndef _STDBOOL_H
#define _STDBOOL_H 1
You are invading the implementations namespace by using a name
that starts with an underscore followed by an upper case character.
See paragraph 7.1.3 in the ANSI/ISO/IEC 9899-1999 standard.
typedef int _Bool;
Once more are you threading on someone elses property.
typedef _Bool bool
const bool false = 0;
const bool true = !false;

Using ``!false'' has no advantages over using ``1'', only disadvantages.

--
Göran Larsson http://www.mitt-eget.com/

[Keith Thompson]

Ian Tuomi <ia*******@co.j yu.fi> writes:

How can I define a boolean value in c? (an value that can only be either
1 or 0) I feel bad for the memory loss when declaring ints for variables
that do not need that much memory.

Read section 9 of the C FAQ, <http://www.eskimo.com/~scs/C-faq/top.html>.

Don't worry too much about using up extra memory. On many systems,
using a variable smaller than a word will cost you more in extra code
size than you save in data size.

--
Keith Thompson (The_Other_Keit h) ks*@cts.com <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://www.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"

[Ian Tuomi]

Keith Thompson wrote:

Read section 9 of the C FAQ, <http://www.eskimo.com/~scs/C-faq/top.html>.
I looked there but it did not say how to save the memory. It only listed
the #define's for TRUE and FALSE.
Don't worry too much about using up extra memory. On many systems,
using a variable smaller than a word will cost you more in extra code
size than you save in data size.

Ok, I just felt bad for all the memory going to waste but I guess that
is irrelevant taking into consideration the current state of computers.
Thanks Everyone.

--
Ian Tuomi
Jyväskylä, Finland

"Very funny scotty, now beam down my clothes."

NOTE: Remove NOSPAM from address

[Jack Klein]

On Fri, 17 Oct 2003 18:59:52 +0200, Tristan Miller
<ps********@not hingisreal.com> wrote in comp.lang.c:

Greetings.

In article <bm**********@p hys-news1.kolumbus. fi>, Ian Tuomi wrote:

How can I define a boolean value in c? (an value that can only be either
1 or 0) I feel bad for the memory loss when declaring ints for variables
that do not need that much memory.
According to the latest C standard, which your compiler may, may not, or may
only partially support:

#include <stdbool.h>

_Bool foo;

Actually, no header is required to use _Bool, which is a built-in
type. <stdbool.h> only defines the macros bool (as a synonym for
_Bool), and the values true and false.
Note that using the new boolean type doesn't guarantee that the compiler is
actually going to set aside just one bit of memory for the variable. In
fact, it probably won't. In practice, the low-level machine code
operations required to test individual bits are typically slower than those
used to compare whole words anyway. So even if you could squeeze your
boolean variables down to a single bit in size, you'd be trading off
execution speed.
Actually _Bool can't use individual bytes, it is an unsigned integer
type. You can have arrays of _Bool and take the address of a _Bool.
Like any other object in C, sizeof(_Bool) must be >= 1, so a _Bool
must occupy at least as much memory as one of the character types.
If you're worried about memory and speed optimizations, concentrate on
choosing efficient algorithms. Microoptimizati ons such as you propose are
generally a waste of the programmer's time for all but the most constrained
execution environments.

Regards,
Tristan

--
Jack Klein
Home: http://JK-Technology.Com
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[Jack Klein]

On Fri, 17 Oct 2003 12:01:46 -0700, "E. Robert Tisdale"
<E.************ **@jpl.nasa.gov > wrote in comp.lang.c:

Ian Tuomi wrote:

How can I define a boolean value in C?
(a value that can only be either 1 or 0)
Don't use the stdbool.h header file.
If you don't have a stdbool.h header file, you can use

#ifndef _STDBOOL_H

Illegal invasion of namespace reserved for the implementation.
#define _STDBOOL_H 1
typedef int _Bool;
Guaranteed syntax error on any compiler that supports the standard C
type _Bool, because _Bool is a built-in type and a keyword. The
header <stdbool.h> is not needed to use the _Bool type on a conforming
compiler.
typedef _Bool bool
const bool false = 0;
const bool true = !false;
#endif _STDBOOL_H

Of course, in many, many ways, this does not act at all like the
standard C type _Bool.

The standard _Bool type is an unsigned type and works like this:

#include <stdbool.h> /* for macros true and false */

_Bool b1 = true;

--b1; /* b1 is now false */
--b1; /* b1 is now true */
--b1; /* b1 is now false again! */

....try that with your lame typedef.

--
Jack Klein
Home: http://JK-Technology.Com
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[Keith Thompson]

Jack Klein <ja*******@spam cop.net> writes:
[...]

Actually _Bool can't use individual bytes, it is an unsigned integer
type. You can have arrays of _Bool and take the address of a _Bool.
Like any other object in C, sizeof(_Bool) must be >= 1, so a _Bool
must occupy at least as much memory as one of the character types.

Typo alert: _Bool can't use individual *bits*.

--
Keith Thompson (The_Other_Keit h) ks*@cts.com <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://www.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"

[Kevin Bracey]

In message <v0************ *************** *****@4ax.com>
Jack Klein <ja*******@spam cop.net> wrote:

Actually _Bool can't use individual bits, it is an unsigned integer
type. You can have arrays of _Bool and take the address of a _Bool.
Like any other object in C, sizeof(_Bool) must be >= 1, so a _Bool
must occupy at least as much memory as one of the character types.

That's only true when you're actually manipulating them in memory. If you had
a _Bool variable that never had its address taken, a smart
compiler would be able to store it in a single bit of memory or of a CPU
register.

And a calling standard could specify that functions returning _Bool actually
returned the result in a CPU's Zero flag, rather than in a general purpose
register - a potentially significant space and speed optimisation.

_Bool allows a number of cunning tricks like that. It just doesn't allow
arrays of bools to be packed bits, which is a shame.

--
Kevin Bracey, Principal Software Engineer
Tematic Ltd Tel: [phone]
182-190 Newmarket Road Fax: [phone]
Cambridge, CB5 8HE, United Kingdom WWW: http://www.tematic.com/