Bug in sprintf?

#1

All,

Why does this fail?

irb(main):009:0> sprintf("%d", ‘08’)
ArgumentError: invalid value for Integer: “08”
from (irb):9:in `sprintf’
from (irb):9

I assume it’s because the 08 is being as an octal number prior to being
changed to a decimal. 01 - 07 work fine, 09 breaks.

But I’m telling sprintf to interpret it as decimal, so why can’t I have
leading zeroes?

Please explain to me how this is expected behavior.

Thanks,
Wes

#2

Wes G. wrote:

I assume it’s because the 08 is being as an octal number prior to being
changed to a decimal. 01 - 07 work fine, 09 breaks.

Because 8 isn’t an octal number. 0-7 are octal.

#3

William C. wrote:

Wes G. wrote:

I assume it’s because the 08 is being as an octal number prior to being
changed to a decimal. 01 - 07 work fine, 09 breaks.

Because 8 isn’t an octal number. 0-7 are octal.

-slaps self- Think before you reply, William.

On second thought, this -does- seem wrong. It doesn’t matter if you
tell it to be decimal, octal or hex, it all comes up with an error on 08
and 09, and not 00 to 07.

#4

William C. wrote:

William C. wrote:

Wes G. wrote:

I assume it’s because the 08 is being as an octal number prior to being
changed to a decimal. 01 - 07 work fine, 09 breaks.

Because 8 isn’t an octal number. 0-7 are octal.

-slaps self- Think before you reply, William.

On second thought, this -does- seem wrong. It doesn’t matter if you
tell it to be decimal, octal or hex, it all comes up with an error on 08
and 09, and not 00 to 07.

Last time, I swear.
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/145509 Says
that it IS trying to be octal because the 0 in front means that. (Why
it means that, I don’t know.)

#5

removed_email_address@domain.invalid wrote:

On Sat, 19 Aug 2006, Wes G. wrote:

All,

Why does this fail?

irb(main):009:0> sprintf("%d", ‘08’)
ArgumentError: invalid value for Integer: “08”
from (irb):9:in `sprintf’
from (irb):9
[…]

But I’m telling sprintf to interpret it as decimal, so why can’t I have
leading zeroes?

Please explain to me how this is expected behavior.
[…]
because:
[…]
ruby uses ‘Integer(s)’ to convert strings to ints and
[…]
Kernel#Integer
[…]
If arg is a +String+, leading radix indicators (+0+, +0b+, and
+0x+) are honored.
[…]
so it’s expected, documented, and consistent with c.

It is not expected, nor documented, because the documentation of sprintf
says:
d | Convert argument as a decimal number.

…which is very explicit in that the argument will be interpreted as a
decimal number, not octal.

Greetings.

#6

On Sat, 19 Aug 2006, Wes G. wrote:

changed to a decimal. 01 - 07 work fine, 09 breaks.

But I’m telling sprintf to interpret it as decimal, so why can’t I have
leading zeroes?

Please explain to me how this is expected behavior.

Thanks,
Wes

because:

 harp:~ > cat a.c
 main(){ char s[42]; int r = sprintf (s, "%d", 07); printf ("%d: 

<%s>\n", r, s); }

 harp:~ > gcc a.c
 harp:~ > a.out
 1: <7>


 harp:~ > cat a.c
 main(){ char s[42]; int r = sprintf (s, "%d", 08); printf ("%d: 

<%s>\n", r, s); }

 harp:~ > gcc a.c
 a.c: In function `main':
 a.c:1: numeric constant contains digits beyond the radix

ruby uses ‘Integer(s)’ to convert strings to ints and

 harp:~ > ri Kernel.Integer
 --------------------------------------------------------- 

Kernel#Integer
Integer(arg) => integer
------------------------------------------------------------------------
Converts arg to a +Fixnum+ or +Bignum+. Numeric types are
converted directly (with floating point numbers being
truncated).
If arg is a +String+, leading radix indicators (+0+, +0b+,
and
+0x+) are honored. Others are converted using +to_int+ and
+to_i+.
This behavior is different from that of +String#to_i+.

         Integer(123.999)    #=> 123
         Integer("0x1a")     #=> 26
         Integer(Time.new)   #=> 1049896590


 harp:~ > ruby -e'  Integer "07"  '

 harp:~ > ruby -e'  Integer "08"  '
 -e:1:in `Integer': invalid value for Integer: "08" (ArgumentError)
         from -e:1

so it’s expected, documented, and consistent with c.

a good pattern to use is:

harp:~ > ruby -e’ atoi = lambda{|s| Integer(s) rescue
%r/(\d+)/.match(s)[1].to_i rescue raise ArgumentError, s};
p(atoi[“08”]); p(atoi[“fubar”]) ’
8
-e:1: fubar (ArgumentError)
from -e:1

because simply falling back on to_i yields

harp:~ > ruby -e’ atoi = lambda{|s| Integer(s) rescue s.to_i};
p(atoi[“08”]); p(atoi[“fubar”]) ’
8
0

regards.

-a

#7

Thanks for the comprehensive response.

Well, I can’t really argue with the C implementation, of course…

BUT

it feels like if I declare my intent to interpret the sprintf input as a
decimal number with %d (there’s a %o if I wanted octal), that is
should allow for leading zeroes.

My intent in writing sprintf("%d", ‘08’) is to say take the string 08
and turn it into the number 8.

It isn’t to say here’s an octal number, please convert it to decimal for
me. If I think the string is octal, I’ll use %o for that.

So in the spirit of what the user expects, I still think this smells
bad.

Feel free to convince me otherwise.

Thanks again,
Wes

#8

What Carlos said :wink:

#9

On 8/18/06, Wes G. removed_email_address@domain.invalid wrote:

My intent in writing sprintf("%d", ‘08’) is to say take the string 08
Thanks again,
Wes

As I see it, there are two separate things: WHAT number you want to
print, and HOW you want it print.

The latter one is specified by the format string.
The former one is specified by argument.

Think of sprintf("%d", 0x1234) or sprintf("%x", 123).

And it happens to be that ‘08’ is in this case the same as 08 and that
is invalid octal number. QED. :wink:

Jano

#10

Carlos wrote:

It is not expected, nor documented, because the documentation of sprintf
says:
d | Convert argument as a decimal number.

…which is very explicit in that the argument will be interpreted as a
decimal number, not octal.

I disagree on that. %d tells sprintf to expect an Integer as the
corresponding argument. Being given a String instead it tries to convert
it by calling Kernel#Integer. This fails for the reasons already
metioned.

Greetings, Matthias

#11

Carlos removed_email_address@domain.invalid writes:

…which is very explicit in that the argument will be interpreted as
a decimal number, not octal.

I think that the problem here is that ruby is performing two
conversions, and the sprintf documentation only mentions one of them.

When you use ‘%d’ in a sprintf(), ruby does a conversion of the
argument to an Integer using Kernel#Integer and then does the
conversion of the Integer to a portion of the output string as
documented.

Similarly, when you use %f in a sprintf(), ruby does a conversion of
the argument using Kernel#float and then does the conversion from
Float to part of the output string as documented.

So, we have:

sprintf("%d",‘08’) ==> ArgumentError
sprintf("%d",‘8’) ==> “8”
sprintf("%d",‘08’.to_i) ==> “8”
sprintf("%f",‘08’) ==> “8.000000”

I think that if you’re hitting this quirk in actual code, your code
needs so .to_i dropped in a few places. I’m actually surprised ruby
does those String=>Integer conversions at all.

#12

I’ll buy that. I did know that my input was a String so I am implicitly
asking for a conversion to occur.

Thanks for the discussion - it helps a lot.

Wes

#13

On Aug 18, 2006, at 8:00 PM, Daniel M. wrote:

When you use ‘%d’ in a sprintf(), ruby does a conversion of the
argument to an Integer using Kernel#Integer and then does the
conversion of the Integer to a portion of the output string as
documented.

How did you figure that out? I started at sprintf.c and browsed a bit
around from rb_f_sprintf on, but I think I was in the wrong path. Or
is it the call to rb_str_to_inum equivalent to Kernel#Integer?

– fxn

#14

Wes G. wrote:

My intent in writing sprintf("%d", ‘08’) is to say take the string 08
and turn it into the number 8.

It isn’t to say here’s an octal number, please convert it to decimal for
me. If I think the string is octal, I’ll use %o for that.

So in the spirit of what the user expects, I still think this smells
bad.

Feel free to convince me otherwise.

Consider it this way:

The format character (%d) is a way to know how the values collected
will be displayed. The values, in this case arguments to %d, are not
intrepreted (necessarily) at the same time as the format characters and
therefor are seperate entities. Taking any [legal] value and passing it
to %d will result in a decimal number printed out.
However, the parsing aspect is entirely different. There is no format
that says: ‘this is how to interpret me’ - other than the syntax.
If you take that away you create ambiguities. If the syntax is longer
how to distinguish a value, it must be explicitly tied to a format
string/character.

Imagine the confusion when you try to
#define FORTY_TWO_HEX %x 2a
#define FORTY_TWO_OCT %o 52
#define FORTY_TOW_DEC %d 42
(Since the two are now linked, you need the format characters. Or
should it be %x 42, %o 42 … you get the idea)

instead of
#define FORTY_TWO_HEX 0x2a
#define FORTY_TWO_OCT 052
#define FORTY_TWO_DEC 42

While it may be easy/convenient to suggest allowing a format character
determine a value, it breaks when not in a specific setting.

#15

Wes G. wrote:

it feels like if I declare my intent to interpret the sprintf input as a
decimal number with %d (there’s a %o if I wanted octal), that is
should allow for leading zeroes.

Declare your intent by doing ‘08’.to_i(10) instead. In fact, declare
your intent in the first place that way.

Expecting sprintf to be automagical the way you expect out of two
incompatible, but perfectly valid interpretations isn’t much to rely on.
Code everything explicitly and you’ll get predictable results.

I’ll join the club of people wondering why the String->Integer coercion
is happening in the first place.

David V.

#16

Carlos wrote:

says:
d | Convert argument as a decimal number.

…which is very explicit in that the argument will be interpreted as a
decimal number, not octal.

The string of characters is interpreted as a decimal number IF IT IS
one. Since you started it with a zero, it’s octal.

Hal

#17

William C. wrote:

Last time, I swear.
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/145509 Says
that it IS trying to be octal because the 0 in front means that. (Why
it means that, I don’t know.)

This comes from C, and is at least 30 years old.

The zero looks like an O, which stands for Octal.

Be glad it’s not Pascal, where 377B is an octal
number (because B looks like an 8).

Hal

#18

Wes G. wrote:

My intent in writing sprintf("%d", ‘08’) is to say take the string 08
and turn it into the number 8.

It isn’t to say here’s an octal number, please convert it to decimal for
me. If I think the string is octal, I’ll use %o for that.

So in the spirit of what the user expects, I still think this smells
bad.

Feel free to convince me otherwise.

I see your point. But most things in Ruby that are stolen from C
behave JUST like the C counterparts. In fact, in many cases they
are just wrappers.

So I can understand why you don’t like it. But my understanding
is that you should blame C.

Hal

#19

Wes G. wrote:

I’ll buy that. I did know that my input was a String so I am implicitly
asking for a conversion to occur.

Thanks for the discussion - it helps a lot.

Actually I failed to take that into account, so what I said
was half nonsense. :slight_smile:

Hal

#20

Carlos wrote:

For that conversion, #to_i could have been used as well, and then ‘09’ would
be interpreted as decimal 9. Why should I expect my string to be passed
through Integer() before formatting? That is not documented.

Why would you pass a string to something that expects a number
anyway?

Hal