value of bit

[Lazyworm]

Hi there

given a primitive type variable, such as "char" or "int", how do i get
the value of each bit in the char? or, how do i get the binary form of
the variable?

Thanks a lot

Lazyworm

[Dann Corbit]

"Lazyworm" <la*********@gmail.comwrote in message
news:18**********************************@l64g2000 hse.googlegroups.com...

Hi there

given a primitive type variable, such as "char" or "int", how do i get
the value of each bit in the char? or, how do i get the binary form of
the variable?

20.8: How can I implement sets or arrays of bits?

A: Use arrays of char or int, with a few macros to access the
desired bit at the proper index. Here are some simple macros to
use with arrays of char:

#include <limits.h /* for CHAR_BIT */

#define BITMASK(b) (1 << ((b) % CHAR_BIT))
#define BITSLOT(b) ((b) / CHAR_BIT)
#define BITSET(a, b) ((a)[BITSLOT(b)] |= BITMASK(b))
#define BITTEST(a, b) ((a)[BITSLOT(b)] & BITMASK(b))

(If you don't have <limits.h>, try using 8 for CHAR_BIT.)

References: H&S Sec. 7.6.7 pp. 211-216.

** Posted from http://www.teranews.com **

[Walter Roberson]

In article <18**********************************@l64g2000hse. googlegroups.com>,
Lazyworm <la*********@gmail.comwrote:

>given a primitive type variable, such as "char" or "int", how do i get
the value of each bit in the char? or, how do i get the binary form of
the variable?

int somevariable = 123;
unsigned char varp = (unsigned char *)&somevariable;
Then varp[0] to varp[sizeof(somevariable)-1] are unsigned char
that can be used to access the individual bytes of the value.

Note the use of unsigned char, not of char. unsigned char is
guaranteed not to have any trap values or padding bits: provided
that the underlying data representation really is binary
(not, for example, trinary on some bizarre computer) then
unsigned char is the only type that you can use to be sure that you
can access the individual bits.

But be careful: varp[0] does not necessarily contain the
"most significant byte" of the value you wish to examine, and
it does not necessarily contain the "least significant byte" either:
varp[0] could end being something in the "middle" of how that
particular systems treats "int" values (seriously!). And there
can be padding bits in numeric values, and there can be padding
bits in structures that use bitfields, and there can be padding
bytes in structures -- so although you might be able to examine
the underlying bytes, it might not always be immediately clear what
those bytes *mean*.
--
"After all, what problems has intellectualism ever solved?"
-- Robert Gilman

[Willem]

Walter Roberson wrote:
) In article <18**********************************@l64g2000hse. googlegroups.com>,
) Lazyworm <la*********@gmail.comwrote:
)
)>given a primitive type variable, such as "char" or "int", how do i get
)>the value of each bit in the char? or, how do i get the binary form of
)>the variable?
)
) int somevariable = 123;
) unsigned char varp = (unsigned char *)&somevariable;
) Then varp[0] to varp[sizeof(somevariable)-1] are unsigned char
) that can be used to access the individual bytes of the value.

NB: The OP wanted bits, not bytes.

Furthermore, using shift and mask operations is much more portable, and
any compiler worth its salt will optimize it to similar performance anyway.
SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

[vippstar]

On Aug 11, 11:28 pm, "Dann Corbit" <[e-mail]:

"Lazyworm" <[e-mail] in message

[...] how do i get the binary form of the variable?

20.8: How can I implement sets or arrays of bits?

<snip rest>

Not the same question.

[pete]

Lazyworm wrote:

Hi there

given a primitive type variable, such as "char" or "int", how do i get
the value of each bit in the char? or, how do i get the binary form of
the variable?

/* BEGIN output from bitstr.c */

0.333333 = 00111110101010101010101010101011
0.666667 = 00111111001010101010101010101011
1.333333 = 00111111101010101010101010101011
2.666667 = 01000000001010101010101010101011
5.333333 = 01000000101010101010101010101011
10.666667 = 01000001001010101010101010101011
21.333334 = 01000001101010101010101010101011
42.666668 = 01000010001010101010101010101011

/* END output from bitstr.c */

/* BEGIN bitstr.c */

#include <limits.h>
#include <stdio.h>

#define STRING "%15f = %s\n"
#define E_TYPE float
#define INITIAL (1.0f / 3)
#define FINAL 50
#define INC(E) ((E) *= 2)

typedef E_TYPE e_type;

void bitstr(char *str, const void *obj, size_t n);

int main(void)
{
e_type e;
char ebits[CHAR_BIT * sizeof e + 1];

puts("\n/* BEGIN output from bitstr.c */\n");
for (e = INITIAL; FINAL >= e; INC(e)) {
bitstr(ebits, &e, sizeof e);
printf(STRING, e, ebits);
}
puts("\n/* END output from bitstr.c */");
return 0;
}

void bitstr(char *str, const void *obj, size_t n)
{
unsigned mask;
const unsigned char *const byte = obj;

while (n-- != 0) {
mask = ((unsigned char)-1 >1) + 1;
do {
*str++ = (char)(mask & byte[n] ? '1' : '0');
mask >>= 1;
} while (mask != 0);
}
*str = '\0';
}

/* END bitstr.c */
--
pete

[vippstar]

On Aug 12, 12:48 am, pete <[e-mail]:
<snip>

#define STRING "%15f = %s\n"
#define E_TYPE float
#define INITIAL (1.0f / 3)
#define FINAL 50
#define INC(E) ((E) *= 2)

typedef E_TYPE e_type;

<snip>

Aren't identifiers starting with E reserved? Or that's only if you
include <errno.h>?

[Keith Thompson]

"Dann Corbit" <dc*****@connx.comwrites:

"Lazyworm" <la*********@gmail.comwrote in message
news:18**********************************@l64g2000 hse.googlegroups.com...

>Hi there

given a primitive type variable, such as "char" or "int", how do i get
the value of each bit in the char? or, how do i get the binary form of
the variable?

20.8: How can I implement sets or arrays of bits?

A: Use arrays of char or int, with a few macros to access the
desired bit at the proper index. Here are some simple macros to
use with arrays of char:

#include <limits.h /* for CHAR_BIT */

#define BITMASK(b) (1 << ((b) % CHAR_BIT))
#define BITSLOT(b) ((b) / CHAR_BIT)
#define BITSET(a, b) ((a)[BITSLOT(b)] |= BITMASK(b))
#define BITTEST(a, b) ((a)[BITSLOT(b)] & BITMASK(b))

(If you don't have <limits.h>, try using 8 for CHAR_BIT.)

References: H&S Sec. 7.6.7 pp. 211-216.

Note that the "If you don't have <limits.h>" clause is very unlikely
to apply these days.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Dann Corbit]

<vi******@gmail.comwrote in message
news:fa**********************************@8g2000hs e.googlegroups.com...

On Aug 11, 11:28 pm, "Dann Corbit" <[e-mail]:

>"Lazyworm" <[e-mail] in message

[...] how do i get the binary form of the variable?

20.8: How can I implement sets or arrays of bits?

<snip rest>

Not the same question.

It answers the question exactly, if you bother to examine the source code.

** Posted from http://www.teranews.com **

[Keith Thompson]

vi******@gmail.com writes:

On Aug 12, 12:48 am, pete <[e-mail]:
<snip>

>#define STRING "%15f = %s\n"
#define E_TYPE float
#define INITIAL (1.0f / 3)
#define FINAL 50
#define INC(E) ((E) *= 2)

typedef E_TYPE e_type;

<snip>

Aren't identifiers starting with E reserved? Or that's only if you
include <errno.h>?

Only identifiers starting with E followed by either a digit or an
uppercase letter. E and E_TYPE are ok.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Jack Klein]

On Mon, 11 Aug 2008 21:37:07 +0000 (UTC), ro******@ibd.nrc-cnrc.gc.ca
(Walter Roberson) wrote in comp.lang.c:

In article <sl********************@snail.stack.nl>,
Willem <wi****@stack.nlwrote:

Walter Roberson wrote:
) In article <18**********************************@l64g2000hse. googlegroups.com>,
) Lazyworm <la*********@gmail.comwrote:

)>given a primitive type variable, such as "char" or "int", how do i get
)>the value of each bit in the char? or, how do i get the binary form of
)>the variable?

) int somevariable = 123;
) unsigned char varp = (unsigned char *)&somevariable;
) Then varp[0] to varp[sizeof(somevariable)-1] are unsigned char
) that can be used to access the individual bytes of the value.

NB: The OP wanted bits, not bytes.

The original pointer wanted "the binary form of the variable".

But if the OP already has a char or an int, as he says he has, he
already has "the binary form of the variable".

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++
http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

[vippstar]

On Aug 12, 4:35 am, Keith Thompson <[e-mail]:

[e-mail] writes:

On Aug 12, 12:48 am, pete <[e-mail]:
<snip>

#define STRING "%15f = %s\n"
#define E_TYPE float
#define INITIAL (1.0f / 3)
#define FINAL 50
#define INC(E) ((E) *= 2)

typedef E_TYPE e_type;

<snip>

Aren't identifiers starting with E reserved? Or that's only if you
include <errno.h>?

Only identifiers starting with E followed by either a digit or an
uppercase letter. E and E_TYPE are ok.

Ah, thanks. :)