[Bug c/60523] New: Warning flag for octal literals

["david at westcontrol dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60523

            Bug ID: 60523
           Summary: Warning flag for octal literals
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david at westcontrol dot com

It would be nice if there were a warning flag that triggered on octal literals. 

Octal literals are rarely used in modern C and C++ code, but can easily be
introduced by mistake - "int x = 050;" appears at first reading to set x to 50,
but in C and C++ the leading 0 means it is interpreted as octal and therefore
sets x to 40 (decimal).

As octal literals are seldom useful, and often confusing or accidental, they
are banned by coding standards like MISRA.  But as they are part of the
language defined by the C and C++ standards, and are used in some existing
code, they obviously cannot be removed.  As a compromise, I would like to
propose the introduction of a warning flags "-Woctal" which would produce a
diagnostic message when a literal is interpreted as an octal number.  Of
preference, this would be included in "-Wextra" (it probably should not be in
"-Wall", since octal literals are valid C and C++).