Dear Maintainer,

*** Reporter, please consider answering these questions, where appropriate ***

   * What led up to the situation?

I used %s conversion to print a string to a file
and %7[^] conversion to scan it back.

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

fscanf (tf, "%7[^]", b) == 01

   * What was the outcome of this action?

false

   * What outcome did you expect instead?

true

*** End of the template - remove these template lines ***

It is not clear whether the format string "%[\0a]" matches the input
string "a" or not.  I interpret the documentation as saying that once
the selector "%[ " has been opened, the format interpreter must find a
matching "]", therefore it must not interpret the embedded "\0" as the
end of the format string. However, trying to use such a format string
causes the compiler to report the warning "format contains NUL", which
suggests that using such a format string involves undefined behaviour.

Hi,

%7[^] is not a valid format string. Quoting the manual, section 12.14.5:

  To read in characters that belong to an arbitrary set of your choice,
  use the ‘%[’ conversion. You specify the set between the ‘[’ character
  and a following ‘]’ character, using the same syntax used in regular
  expressions for explicit sets of characters. As special cases:

  - A literal ‘]’ character can be specified as the first character of the set.

[...]

  - If a caret character ‘^’ immediately follows the initial ‘[’, then
    the set of allowed input characters is everything except the
    characters listed.

In your case, you want to match up to 7 characters, but given there is
no character or list of characters after the caret, it's not clear what
you want to achieve. If you want to match everything but a ‘[’, you
should use %7[^]] .

Regards,
Aurelien

Hi,

According to the C standard, \0 or the NUL character is the end of
string. Therefore the string passed to fscanf is simply "%[", which is
invalid.

As explained above, the compiler is right about that.

Regards
Aurelien

Hi,

This is the basic of the C language. It has nothing to do with the GNU
libc.

I disagree there. This documentation is about the GNU C library, not a
basic C course.

Regards
Aurelien

Hi,

We are here talking about *string* functions of the C standard. String
functions in this context are defined as NULL terminated. The beginning
of section 12.14 makes clear that the argument of the fscanf function is
a format *string*.

The argz functions do not operate on strings. They operate on *vector of
strings*. See section 5.15.

Indeed you are allow to use your own convention for a library, but But a
string is well defined in the C standard in the context of the string
functions.

Regards
Aurelien

Hi,

Your definition of "empty set" is quite vague. What you want is clearly
defined in the section 12.14.3, that is %7s or %7S.

I don't see how things can be improved further. But if you have a
wording suggestion, please submit one. Otherwise, I'll just close the
bug.

Regards
Aurelien