Re: Passing member variable as parameter to the base class constructor: warning expected but not seen

[Ronny Meeus <ronny.meeus@gmail.com>]

Op wo 22 jun. 2022 om 13:51 schreef Jonathan Wakely <jwakely.gcc@gmail.com>:
>
> On Wed, 22 Jun 2022 at 12:30, Ronny Meeus via Gcc-help
> <gcc-help@gcc.gnu.org> wrote:
> >
> > Hello
> >
> > I have a small test program (see below) that uses a member variable
> > (a) of a derived class (A) as a parameter when calling the constructor
> > of the base class (A_base).
> > In fact this is "wrong" code since the base class constructor is
> > called with an un-initialized variable as input.
> >
> > I would expect that the compiler generates a warning/error for this
> > since the behavior completely depends on the contents of the memory
> > where the object was allocated from.
> > In the example code I use a placement new to actually show that the
> > value seen in the constructor of the base class is the value I used to
> > fill the memory with.
> >
> > I tried it with different gcc versions but none of these are
> > generating a warning/error for this while other tools like coverity or
> > sonarqube just report the issue ...
> > Is it expected that there is no warning generated or do I need to pass
> > extra compiler options to generate this warning?
> >
> > I compile the program like this:
> > $ g++ -Wall -Wextra -std=gnu++11 /tmp/a.cc
>
> You didn't say which version of GCC you're using, but GCC 12 warns
> about this now:
>
> w.C: In constructor 'A::A()':
> w.C:16:17: warning: member 'A::a' is used uninitialized [-Wuninitialized]
>   16 |     A(): A_base(a) {
>      |                 ^
>
> Older versions do not warn.

Thanks for the feedback.
For completeness I tested with:
10.3.0
7.3.0
4.8.5
 (I know it are rather old versions but we work on embedded targets)

Best regards,
Ronny