Bug #13315: Single "%" at the end of `printf` format string appears in the result

• Status: Closed
• Assignee: Eregon (Benoit Daloze)
• Target version: -
• Backport: 2.2: WONTFIX, 2.3: WONTFIX, 2.4: UNKNOWN

[nobu (Nobuyoshi Nakada)]

Is this intentional?

printf("%") #=> "%"

printf in glibc does print nothing, gcc warns though.

#include <stdio.h>

int main(void)
{
  printf("%");
  return 0;
}

$ gcc fmt.c && ./a.out 
fmt.c: In function ‘main’:
fmt.c:5:10: warning: spurious trailing ‘%’ in format [-Wformat=]
   printf("%");
          ^

printf command of bash errs.

$ printf "%"
-bash: printf: `%': missing format character

[morishin (Shintaro Morikawa)]

I believe this is not intentional, so created a pull-request on GitHub.
https://github.com/ruby/ruby/pull/1560

This change makes ruby raise error for printf("%") though C just shows warning because this change will drop displayed "%" silently for developers if this shows just warning instead of raising error.

I updated rubyspec too.
https://github.com/ruby/spec/issues/401

[sorah (Sorah Fukumori)]

• Assignee set to matz (Yukihiro Matsumoto)

Matz, is this intentional?

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

[matz (Yukihiro Matsumoto)]

When I wrote the original code, it was intentional, but without any specific reason.
It's OK for me to raise an error for this case.

Matz.

[Eregon (Benoit Daloze)]

• Assignee changed from matz (Yukihiro Matsumoto) to Eregon (Benoit Daloze)

[Eregon (Benoit Daloze)]

• Status changed from Assigned to Closed

Applied in changeset trunk|r58890.

---

Raise ArgumentError if sprintf format string ends with %

• Add tests and specs. See ruby/spec#401.
  Patch by Yuta Iwama and Shintaro Morikawa.
  [ruby-core:80153] [Bug #13315] [Fix GH-1560]

[usa (Usaku NAKAMURA)]

• Backport changed from 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN to 2.2: WONTFIX, 2.3: WONTFIX, 2.4: UNKNOWN

[nobu (Nobuyoshi Nakada)]

• Related to Bug #20439: Invalid string format with n$ flag is ignored in some case added

[nobu (Nobuyoshi Nakada)]

• Related to Bug #20438: String format "%\n" and "%\0" does not raise format error added