[Bug c++/54361] New: Compiling for c++11 gives a warning on scanf() with %as format specifier

[Bug c++/54361] New: Compiling for c++11 gives a warning on scanf() with %as format specifier

[strikosn at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54361

             Bug #: 54361
           Summary: Compiling for c++11 gives a warning on scanf() with
                    %as format specifier
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: strikosn@gmail.com


Target: x86_64-unknown-linux-gnu
Configured with: /home/utils/src/gcc-4.7.0/configure
--prefix=/home/utils/gcc-4.7.0 --enable-languages=c,c++,objc,fortran
--with-gmp=/home/utils/gmp-5.0.2-static
--with-mpfr=/home/utils/mpfr-3.1.0-static --with-mpc=/home/utils/mpc-0.9-static
--with-as=/home/utils/binutils-2.21.1/bin/as
--with-ld=/home/utils/binutils-2.21.1/bin/ld
Thread model: posix
gcc version 4.7.0 (GCC)

Source code attached as c.cpp

$ g++ -std=c++11 -Wall -Werror c.cpp
c.cpp: In function 'int main()':
c.cpp:10:26: error: format '%a' expects argument of type 'float*', but argument
2 has type 'char**' [-Werror=format]
c.cpp:7:7: error: unused variable 'a' [-Werror=unused-variable]
cc1plus: all warnings being treated as errors

[Bug c++/54361] Compiling for c++11 gives a warning on scanf() with %as format specifier

[strikosn at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54361

--- Comment #1 from Nick Strikos <strikosn at gmail dot com> 2012-08-23 23:35:31 UTC ---
Created attachment 28075
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28075
Testcase

[Bug c++/54361] Compiling for c++11 gives a warning on scanf() with %as format specifier

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54361

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-08-23 23:54:24 UTC ---
The warning is correct, %as (the oldish GNU extension) clashes with ISO C99 a
modifier for hex floats, if you want to allocate memory, use %ms instead, which
is the standard way of doing the same.

[Bug c++/54361] Compiling for c++11 gives a warning on scanf() with %as format specifier

[strikosn at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54361

strikosn at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #3 from strikosn at gmail dot com 2012-08-24 00:04:39 UTC ---
Right, %ms is standardized and solves the problem. But the whole thing is
confusing because previously working C++ programs can no more compile with
-std=c++11 or -std=gnu++11, and this has nothing to do with the C++11 standard.

[Bug c++/54361] Compiling for c++11 gives a warning on scanf() with %as format specifier

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54361

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-08-24 08:02:39 UTC ---
It has a lot with C++11, if you read that standard, you'll see that for C
library stuff it refers to ISO C99 standard.  Therefore, using %as is really
invalid in C++11 programs.