# Bug in ruby printf/sprintf **URL:** \ **Category:** Ruby\ **Created:** [July 28, 2006, 9:32pm UTC](https://www.ruby-forum.com/t/bug-in-ruby-printf-sprintf/100419 "2006-07-28T21:32:31Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [July 28, 2006, 9:32pm UTC](https://www.ruby-forum.com/t/bug-in-ruby-printf-sprintf/100419/1 "2006-07-28T21:32:31Z")
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 ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [July 28, 2006, 9:42pm UTC](https://www.ruby-forum.com/t/bug-in-ruby-printf-sprintf/100419/2 "2006-07-28T21:42:15Z")
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. ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [July 28, 2006, 9:49pm UTC](https://www.ruby-forum.com/t/bug-in-ruby-printf-sprintf/100419/3 "2006-07-28T21:49:18Z")
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 ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [July 29, 2006, 11:16am UTC](https://www.ruby-forum.com/t/bug-in-ruby-printf-sprintf/100419/4 "2006-07-29T11:16:14Z")
Hi,] In message “Re: Bug in ruby printf/sprintf” on Sat, 29 Jul 2006 04:45:13 +0900, “removed\_email\_address@domain.invalid” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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. ``` ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [July 29, 2006, 11:40am UTC](https://www.ruby-forum.com/t/bug-in-ruby-printf-sprintf/100419/5 "2006-07-29T11:40:50Z")
On 7/29/06, Yukihiro M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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!