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

[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.