Re: [PATCH] Use C99-compliant scanf under _GNU_SOURCE with C99/C++11 and higher.

[Florian Weimer <fweimer at redhat dot com>]

* Zack Weinberg:

> +* An archaic GNU extension to scanf, under which '%as', '%aS', and '%a[...]'
> +  meant to scan a string and allocate space for it with malloc, is now
> +  restricted to programs compiled in C89 or C++98 mode with _GNU_SOURCE
> +  defined.  This extension conflicts with C99's use of '%a' to scan a
> +  hexadecimal floating-point number, which is now available to programs
> +  compiled as C99 or C++11 or higher, regardless of _GNU_SOURCE.
> +
> +  POSIX.1-2008 includes the feature of allocating a buffer for string input
> +  with malloc, using the modifier letter 'm' instead.  Programs using
> +  '%as', '%aS', or '%a[...]' with the old GNU meaning should change to
> +  '%ms', '%mS', or '%m[...]' respectively.  Programs that wish to use the
> +  C99 '%a' no longer need to avoid _GNU_SOURCE.
> +
> +  GCC's -Wformat warnings can detect most uses of this extension, as long
> +  as all functions that call vscanf, vfscanf, or vsscanf are annotated with
> +  __attribute__ ((format (scanf, ...))).

What's the state of GCC warnings?  Does GCC already anticipate this
change?

Thanks,
Florian