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

[Mark A. Odell]

Ian Tuomi <ia*******@co.j yu.fi> wrote in
news:bm******** **@phys-news1.kolumbus. fi:

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.

You can't do what I think you really want in C, this will give you
something that can only hold a one or a zero:

struct MyBool
{
int boolean : 1;
};

struct MyBool flag;

flag.boolean = 1;

This still uses a full int though. If you really want to have a boolean
that uses one bit only then use an 8051 with a C compiler in non-standard
mode and declare your booleans with the 'bit' type.
--
- Mark ->
--

[Johan Aurér]

On Fri, 17 Oct 2003, Mark A. Odell wrote:

You can't do what I think you really want in C, this will give you
something that can only hold a one or a zero:

struct MyBool
{
int boolean : 1;
};

struct MyBool flag;

flag.boolean = 1;

Only works if the implementation treats int bitfields as unsigned.

--
au***@axis.com

[Irrwahn Grausewitz]

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

Unless you are writing code for a platform with extremely limited
resources you shouldn't bother at all.

Regards
--
Irrwahn
(ir*******@free net.de)

[Derk Gwen]

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

I generally use
typedef unsigned char bool;
enum {true=1,false=0 };
and don't worry about how tightly it's packed. I got 256Mbytes of real memory
and gigabytes of virtual.

If you have a number of booleans in one structure, you can pack them
one bit at a time,
struct {
int empty:1;
int nullable:1;
int productive:1;
int weight:7;
int leftrcr:1;
int rightrcr:1;
int embedding:1;
...
}
which can trade space for time.

--
Derk Gwen http://derkgwen.250free.com/html/index.html
I think that's kinda of personal; I don't think I should answer that.

[Tristan Miller]

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;

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.

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

--
_
_V.-o Tristan Miller [en,(fr,de,ia)] >< Space is limited
/ |`-' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-= <> In a haiku, so it's hard
(7_\\ http://www.nothingisreal.com/ >< To finish what you

[Noah Roberts]

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.

The problem is that in todays computers access to single bits isn't
really available. You work with entiry bytes or sometimes larger, use
and/or/xor, and compare with 0. Therefor there is no way to really do
this unless you have more than one boolean value you want to hold. If
that is the case you use bit manipulations to set and unset bits on
something like a u_char or whatever.

NR

[E. Robert Tisdale]

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
#define _STDBOOL_H 1
typedef int _Bool;
typedef _Bool bool
const bool false = 0;
const bool true = !false;
#endif _STDBOOL_H

[Christopher Benson-Manica]

E. Robert Tisdale <E.************ **@jpl.nasa.gov > spoke thus:

Don't use the stdbool.h header file.

What? Why not?

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Jeremy Yallop]

E. Robert Tisdale wrote:

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.

Do you mean "Use the stdbool.h header"?
If you don't have a stdbool.h header file, you can use

#ifndef _STDBOOL_H
#define _STDBOOL_H 1
typedef int _Bool;
typedef _Bool bool
Missing semicolon.
const bool false = 0;
const bool true = !false;
There are at least two serious problems with these definitions:

* The values of `false' and `true' cannot be used in constant
expressions.

* The header cannot be used in multiple source files. Using these
variables in more than one translation unit causes undefined
behaviour, due to multiple external definitions for `false' and
`true'.

Further, there doesn't seem to be a good reason for `true' and `false'
to be addressable.

Arguments could be made for using either an enum or macros, but const
variables are not the right way to do this. The standards people knew
what they were doing when they made `false' and `true' macros, you
know. In particular, they understood the difference between the way
`const' works in C and in C++.

Also, note that the _Bool defined here doesn't behave much like the
standard _Bool; I'd call it something else to avoid possible
confusion.
#endif _STDBOOL_H

The grammar doesn't allow tokens after #endif.

Jeremy.