https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203
mauro russo <ing.russomauro at gmail dot com> changed:
What |Removed |Added
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CC| |ing.russomauro at gmail dot com
--- Comment #25 from mauro russo <ing.russomauro at gmail dot com> ---
Hello,
I was going to post a new potential bug (for gcc 14.2) and then found two
exist: PR 60212 and this one, too.
I will paste here below my intended message with the error description, but
note that in my description a missing warning happens also for trivial type
when the value-initialization is used.
I wasn't sure whether to post this message here or in PR 60212.
I found the case while studying differences about user-provided and
non-user-provided explicitly-defaulted default constructors.
In the following code:
struct X{
X() = default;
// int m;
};
//X::X() = default;
int main()
{
X x;
return 0;
}
gcc raises a warning about unused variable x,
but in the following other code (https://godbolt.org/z/36WKzbvP6)
struct X{
X(); // = default;
// int m;
};
X::X() = default;
int main()
{
X x;
return 0;
}
no warning is issued.
Well, in second case, the explictly-defaulted default constructor is
user-provided, which also leads it not to be trivial (and, consequently, the
type neither).
However, in both cases, no initialization of any base or non-static data member
is done, and nothing changes also if a data member "int m;" is added (with no
default member initializer).
I cannot figure out what motivation may lead to a different behaviour.
In particular, if the opposite behaviour would have happened, I could have
supposed the error to be related to the vacuous-initialization when
non-user-provided (first case).
Additionally, note that if 'x' is value-initialized ("X x{};"), then the
warning disappears in both cases (trivial or non-trivial), regardless of adding
or not an "int m;" data member, where the only theoretical difference (beyond
the 'trivial' and consequent 'vacuous-initialization') is that no
zero-initialization is performed as first step of the value-initialization (see
https://eel.is/c++draft/dcl.init.general#9.1), before the
default-initialization (that does nothing).
