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comp.lang.ruby

Bug in ruby printf/sprintf

paul.dlug@gmail.com

7/28/2006 7:28:00 PM

I have encountered what appears to be a bug in ruby's printf/sprintf

This code:

str = "test"
printf "|%010s|", str

Generates this output:
| test|

However in C and perl, the same code generates this output:
|000000test|

The latter output is correct according to the man pages, according to
the ruby doc for printf/sprintf the behavior should be the same.

Has anyone else encountered this? Is there something I'm missing here
or is there a workaround for it if it is a bug?


Thanks,
Paul
4 Answers

Tiberius

7/28/2006 7:36:00 PM

0

The equivalent C program under RedHat Linux 3 update 6 x86_64 produces
| test|

Also, I ran your ruby code in ruby 1.8.4 (2006-12-24) and it also
produces the same results as the C code does.



paul.dlug@gmail.com wrote:
> I have encountered what appears to be a bug in ruby's printf/sprintf
>
> This code:
>
> str = "test"
> printf "|%010s|", str
>
> Generates this output:
> | test|
>
> However in C and perl, the same code generates this output:
> |000000test|
>
> The latter output is correct according to the man pages, according to
> the ruby doc for printf/sprintf the behavior should be the same.
>
> Has anyone else encountered this? Is there something I'm missing here
> or is there a workaround for it if it is a bug?
>
>
> Thanks,
> Paul

paul.dlug@gmail.com

7/28/2006 7:44:00 PM

0


Tiberius wrote:
> The equivalent C program under RedHat Linux 3 update 6 x86_64 produces
> | test|
>
> Also, I ran your ruby code in ruby 1.8.4 (2006-12-24) and it also
> produces the same results as the C code does.

That's interesting. I just tried the same on linux (Gentoo) and you're
correct, printf in C behaves the same way there. In Mac OS X (10.4) and
FreeBSD (6.1) it does zero pad it as does perl on all platforms. I
wonder why I haven't hit this before and what the reason for the
difference is. Time to take a look at the doc's for the linux version.


--Paul

Yukihiro Matsumoto

7/29/2006 9:13:00 AM

0

Hi,]

In message "Re: Bug in ruby printf/sprintf"
on Sat, 29 Jul 2006 04:45:13 +0900, "paul.dlug@gmail.com" <paul.dlug@gmail.com> writes:

|That's interesting. I just tried the same on linux (Gentoo) and you're
|correct, printf in C behaves the same way there. In Mac OS X (10.4) and
|FreeBSD (6.1) it does zero pad it as does perl on all platforms. I
|wonder why I haven't hit this before and what the reason for the
|difference is. Time to take a look at the doc's for the linux version.

From Linux man page printf(3):

0 The value should be zero padded. For d, i, o, u, x,
X, a, A, e, E, f, F, g, and G conversions, the converted
value is padded on the left with zeros rather than
blanks. If the 0 and - flags both appear, the 0 flag is
ignored. If a precision is given with a numeric
conversion (d, i, o, u, x, and X), the 0 flag is
ignored. For other conversions, the behavior is
undefined.

It's behavior is undefined, so that some fills with zeros and others
just ignore. Don't use zero with %s specifier if you want portable
behavior.

matz.

Leslie Viljoen

7/29/2006 9:41:00 AM

0

On 7/29/06, Yukihiro Matsumoto <matz@ruby-lang.org> wrote:
> Hi,]
>
> In message "Re: Bug in ruby printf/sprintf"
> on Sat, 29 Jul 2006 04:45:13 +0900, "paul.dlug@gmail.com" <paul.dlug@gmail.com> writes:
>
> |That's interesting. I just tried the same on linux (Gentoo) and you're
> |correct, printf in C behaves the same way there. In Mac OS X (10.4) and
> |FreeBSD (6.1) it does zero pad it as does perl on all platforms. I
> |wonder why I haven't hit this before and what the reason for the
> |difference is. Time to take a look at the doc's for the linux version.
>
> From Linux man page printf(3):
>
> 0 The value should be zero padded. For d, i, o, u, x,
> X, a, A, e, E, f, F, g, and G conversions, the converted
> value is padded on the left with zeros rather than
> blanks. If the 0 and - flags both appear, the 0 flag is
> ignored. If a precision is given with a numeric
> conversion (d, i, o, u, x, and X), the 0 flag is
> ignored. For other conversions, the behavior is
> undefined.
>
> It's behavior is undefined, so that some fills with zeros and others
> just ignore. Don't use zero with %s specifier if you want portable
> behavior.

So here's portable:
print "|#{str.rjust(10, "0")}|"

Sorry to insult everyone's intelligence!