https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118346
Bug ID: 118346
Summary: Access to member inherited from virtual base class
forbidden in GCC with temporary null pointer instance
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wangbopku15 at gmail dot com
Target Milestone: ---
The following code does not compile in GCC:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
struct A { int i; };
struct C : virtual public A { };
int main (){
auto res = ((C*)0)->i;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The diagnostic is:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>: In function 'int main()':
<source>:5:25: error: invalid access to non-static data member 'A::i' in
virtual base of NULL object
5 | auto res = ((C*)0)->i;
| ^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Actually, I'm not sure whether this should be valid, but the following code
appears to work in GCC:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
struct A { int i; };
struct C : virtual public A { };
int main (){
auto res = ((C*)0)->A::i;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
https://godbolt.org/z/rY9Yh6jrG
Also note that if the instance here is not a temporary variable, it works:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
struct A { int i; };
struct C : virtual public A { };
int main (){
auto no_temporary = (C*)0;
auto res = no_temporary->i;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
https://godbolt.org/z/Mj4ffoahE
MSVC, EDG, and Clang always accept it:
https://godbolt.org/z/aq6ojdPz7
