how to get 0.000001 with printf?

[Mandar Mitra]

Hello,

I'd like to print floating point numbers without trailing zeros.
I tried using %g, but now small numbers are printed in the %e
style ("Style e is used if the exponent from its conversion is
less than -4"). Is there some way to control this number (-4)?
I.e. can I get printf to print something like 0.0000001, but no
trailing zeros? Or should I do this by hand?

Thanks,
Mandar.

[Mark McIntyre]

On 27 Oct 2005 23:52:48 -0700, in comp.lang.c , "Mandar Mitra"
<ma**********@g mail.com> wrote:

Hello,

I'd like to print floating point numbers without trailing zeros.

I presume you mean you want 0.0100000 to print as "0.01" and
0.00001000 to print as "0.00001".

You need to roll your own code. You'd first of all have to work out
how many of the decimals were significant, then create a format string
via sprintf, then printf the number.
Working out how many decimals are significant is quite interesting.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >

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[Jordan Abel]

On 2005-10-28, Mark McIntyre <ma**********@s pamcop.net> wrote:

On 27 Oct 2005 23:52:48 -0700, in comp.lang.c , "Mandar Mitra"
<ma**********@g mail.com> wrote:

Hello,

I'd like to print floating point numbers without trailing zeros.

I presume you mean you want 0.0100000 to print as "0.01" and
0.00001000 to print as "0.00001".

You need to roll your own code. You'd first of all have to work out
how many of the decimals were significant, then create a format string
via sprintf, then printf the number.
Working out how many decimals are significant is quite interesting.

Probably the easiest way would be to simply truncate it to a given
amount, say, {FLT,DBL,LDBL}_ DIG and then cut off trailing zeros from
there.

A more exact, but slower, way, would be to try each amount of digits
in turn and see if the result of such compares equal to the
original.

[William Hughes]

Mandar Mitra wrote:

Hello,

I'd like to print floating point numbers without trailing zeros.

Right. You want to print .20000 as .2 but print
..19999 as .19999. This is a pretty stuipid thing to do,
so there is no built in way of doing it.
You need to do it by hand. Here's one way

-save the sign and convert to absolute value

-save the integer part of the numbers and
reduce them to less than 1.

- Round off your numbers to your desired maximum
number of digits.

- sprintf the number into a buffer, specifiying
the maximum number of digits

- remove trailing zeros (or replace with blanks
if your want constant field width)

- sprintf the integer parts, then strcat the fractional
parts (starting at the second character to lose
the zero)

-add the sign back to the front, (and pad with blanks
at the front if you want constant field width)
Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

-William Hughes

[Jordan Abel]

On 2005-10-29, William Hughes <wp*******@hotm ail.com> wrote:

Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

I can't think of any situation where they could mean different
things to C - and C itself does not provide for a way to easily
track significant figures.

[Kenny McCormack]

In article <sl************ *******@random. yi.org>,
Jordan Abel <jm****@purdue. edu> wrote:

On 2005-10-29, William Hughes <wp*******@hotm ail.com> wrote:

Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

I can't think of any situation where they could mean different
things to C - and C itself does not provide for a way to easily
track significant figures.

Ask yourself who *reads* the output of programs.

Hint: It isn't a C program (nor is it the C standard)

[Jordan Abel]

On 2005-10-29, Kenny McCormack <ga*****@yin.in teraccess.com> wrote:

In article <sl************ *******@random. yi.org>,
Jordan Abel <jm****@purdue. edu> wrote:

On 2005-10-29, William Hughes <wp*******@hotm ail.com> wrote:

Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

I can't think of any situation where they could mean different
things to C - and C itself does not provide for a way to easily
track significant figures.

Ask yourself who *reads* the output of programs.

Hint: It isn't a C program (nor is it the C standard)

The format requested in this thread is analogous to the "general
number" format in programs such as Microsoft Excel. That it exists
and is the default tells me that there are certainly some situations
in which the _humans_ reading the output of the program will not
have a problem with supression of trailing zeros.

[Mark McIntyre]

On Sat, 29 Oct 2005 15:38:15 GMT, in comp.lang.c ,
ga*****@yin.int eraccess.com (Kenny McCormack) wrote:

In article <sl************ *******@random. yi.org>,
Jordan Abel <jm****@purdue. edu> wrote:

On 2005-10-29, William Hughes <wp*******@hotm ail.com> wrote:

Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

I can't think of any situation where they could mean different
things to C - and C itself does not provide for a way to easily
track significant figures.

Ask yourself who *reads* the output of programs.

Well, fundamentally .2, .20 and .200 cannnot actually mean different
things, so the difference is nothing more than cosmetic. What were you
thinking of?

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >

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[Kenny McCormack]

In article <r1************ *************** *****@4ax.com>,
Mark McIntyre <ma**********@s pamcop.net> wrote:

On Sat, 29 Oct 2005 15:38:15 GMT, in comp.lang.c ,
ga*****@yin.in teraccess.com (Kenny McCormack) wrote:

In article <sl************ *******@random. yi.org>,
Jordan Abel <jm****@purdue. edu> wrote:

On 2005-10-29, William Hughes <wp*******@hotm ail.com> wrote:
Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

I can't think of any situation where they could mean different
things to C - and C itself does not provide for a way to easily
track significant figures.

Ask yourself who *reads* the output of programs.

Well, fundamentally .2, .20 and .200 cannnot actually mean different
things, so the difference is nothing more than cosmetic. What were you
thinking of?

They mean very different things, as I am sure you are well aware.

[Keith Thompson]

Mark McIntyre <ma**********@s pamcop.net> writes:

On Sat, 29 Oct 2005 15:38:15 GMT, in comp.lang.c ,
ga*****@yin.int eraccess.com (Kenny McCormack) wrote:

In article <sl************ *******@random. yi.org>,
Jordan Abel <jm****@purdue. edu> wrote:

On 2005-10-29, William Hughes <wp*******@hotm ail.com> wrote:
Normally, .2, .20, .200 mean different things, so supressing
the trailing zeros usually a BAD THING.

I can't think of any situation where they could mean different
things to C - and C itself does not provide for a way to easily
track significant figures.

Ask yourself who *reads* the output of programs.

Well, fundamentally .2, .20 and .200 cannnot actually mean different
things, so the difference is nothing more than cosmetic. What were you
thinking of?

They certainly can mean different things. Depending on the context,
they can imply different levels of precision. ".2" can (sometimes)
mean anything from 0.15 to 0.25, whereas ".200" can mean anything from
0.1995 to 0.2005 (I'm ignoring the question of whether the endpoints
are included in the range).

Given:

double x = 0.2;
double y = 0.234;

"0.2" can be the result of printing either x or y; "0.200" cannot.

It's also valid to consider .2 and .200 both to represent the same
exact real value (one that's not representable in binary
floating-point). The interpretation depends on the context.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.