Floating point number to binary

[Gaurav Verma]

Hi,

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help me
out with it?

Thanks
Gaurav
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et

[osmium]

Gaurav Verma writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help me
out with it?

I don't think it is very clear what you are trying to do. For example, what
do you think the binary representation of a decimal point is? Are you
trying to learn something, as opposed to than actually *doing* something?
If so, what are you trying to learn?

[Brian Gough]

ve**********@gm ail.com (Gaurav Verma) writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help me
out with it?

If you want the underlying IEEE representation of a floating point
number you can use a union to access the individual bytes.

e.g. union { double d; struct { unsigned char byte[8]; } ieee ; } u;

--
Brian Gough

Network Theory Ltd,
Publishing "An Introduction to GCC" --- http://www.network-theory.co.uk/gcc/

[CBFalconer]

Brian Gough wrote:

ve**********@gm ail.com (Gaurav Verma) writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help
me out with it?

If you want the underlying IEEE representation of a floating point
number you can use a union to access the individual bytes.

e.g. union {double d; struct { unsigned char byte[8];} ieee ; } u;

No you can't, at least not portably. What you can do is set up a
pointer to the storage and access it via that.

#include <stdio.h>

int main(void)
{
double d;
unsigned char *p;
unsigned int i;

d = 123.4; /* or whatever */
p = (unsigned char *)(&d);
for (i = 0; i < sizeof(double); i++) {
printf("%2x ", p[i]);
/* do other things with p[i] */
}
putchar('\n');
return 0;
}

--
"This is a wonderful answer. It's off-topic, it's incorrect,
and it doesn't answer the question." -- Richard Heathfield

"I support the Red Sox and any team that beats the Yankees"

[Dan Pop]

In <41************ ***@yahoo.com> CBFalconer <cb********@yah oo.com> writes:

Brian Gough wrote:

ve**********@gm ail.com (Gaurav Verma) writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help
me out with it?
If you want the underlying IEEE representation of a floating point
number you can use a union to access the individual bytes.

e.g. union {double d; struct { unsigned char byte[8];} ieee ; } u;

No you can't, at least not portably.

Care to elaborate on the portability problems of:

union { double d; unsigned char bytes[sizeof(double)]; } u;

?
What you can do is set up a
pointer to the storage and access it via that.

Both aliasing methods are equally blessed by the C standard. And both
are plagued by byte order issues.

C99's %a printf conversion descriptor is the closest solution to the OP's
problem.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Currently looking for a job in the European Union

[Ben Pfaff]

Brian Gough <bj*@network-theory.co.uk> writes:

ve**********@gm ail.com (Gaurav Verma) writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help me
out with it?

If you want the underlying IEEE representation of a floating point
number you can use a union to access the individual bytes.

e.g. union { double d; struct { unsigned char byte[8]; } ieee ; } u;

There's no need to put the array in a structure:
union { double d; unsigned char ieee[8]; } u;
--
Ben Pfaff
email: bl*@cs.stanford .edu
web: http://benpfaff.org

[Ben Pfaff]

CBFalconer <cb********@yah oo.com> writes:

Brian Gough wrote:

ve**********@gm ail.com (Gaurav Verma) writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help
me out with it?

If you want the underlying IEEE representation of a floating point
number you can use a union to access the individual bytes.

e.g. union {double d; struct { unsigned char byte[8];} ieee ; } u;

No you can't, at least not portably. What you can do is set up a
pointer to the storage and access it via that.

Assuming IEEE representation is inherently not portable. I don't
think the above union will make the code less portable.
--
int main(void){char p[]="ABCDEFGHIJKLM NOPQRSTUVWXYZab cdefghijklmnopq rstuvwxyz.\
\n",*q="kl BIcNBFr.NKEzjwC IxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+= strchr(p,*q++)-p;if(i>=(int)si zeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}

[CBFalconer]

Dan Pop wrote:

CBFalconer <cb********@yah oo.com> writes:

Brian Gough wrote:
.... snip ...

If you want the underlying IEEE representation of a floating
point number you can use a union to access the individual bytes.

e.g. union {double d; struct {unsigned char byte[8];} ieee ;} u;

No you can't, at least not portably.

Care to elaborate on the portability problems of:

union { double d; unsigned char bytes[sizeof(double)]; } u;

As I understand it accessing a union member as other than the type
that was stored in it is either implementation or undefined.

--
"This is a wonderful answer. It's off-topic, it's incorrect,
and it doesn't answer the question." -- Richard Heathfield

"I support the Red Sox and any team that beats the Yankees"

[Old Wolf]

Brian Gough <bj*@network-theory.co.uk> wrote:

ve**********@gm ail.com (Gaurav Verma) writes:

I want to convert a floating point number (or a decimal number say
123.456) into binary notation using a C program. Can somebody help me
out with it?

If you want the underlying IEEE representation of a floating point
number you can use a union to access the individual bytes.

e.g. union { double d; struct { unsigned char byte[8]; } ieee ; } u;

This is undefined behaviour; to be portable you should go:
unsigned char *ptr = (unsigned char *)&d;
and then access the first (sizeof d) bytes of ptr.

Also note that the size of double is not required to be 8, and it is
not required to use IEEE format (although usually it is).

[Jack Klein]

On Thu, 16 Sep 2004 19:08:59 GMT, CBFalconer <cb********@yah oo.com>
wrote in comp.lang.c:

Dan Pop wrote:

CBFalconer <cb********@yah oo.com> writes:

Brian Gough wrote:
... snip ...
If you want the underlying IEEE representation of a floating
point number you can use a union to access the individual bytes.

e.g. union {double d; struct {unsigned char byte[8];} ieee ;} u;

No you can't, at least not portably.

Care to elaborate on the portability problems of:

union { double d; unsigned char bytes[sizeof(double)]; } u;

As I understand it accessing a union member as other than the type
that was stored in it is either implementation or undefined.

....except for unsigned char, which is the one and only bullet proof,
invulnerable type in C. Since unsigned char is the only type required
not to have trap representations , any object that your program has the
right to access, it may access as an array of unsigned chars without
invoking the ever dreaded UB.

See particularly paragraphs 4 and 5 of 6.2.6.1.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html