https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95407
Bug ID: 95407
Summary: G++ allows access to base class members from a friend
of a derived class
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dragondreamer at live dot com
Target Milestone: ---
G++ (at least trunk, 10.1.0, 9.3, 9.2) successfully compiles the following
code:
// ===================================
#include <iostream>
struct test_base
{
protected:
static constexpr int value = 123;
};
template<typename Base>
struct ignored_friend_declaration
{
static void bug()
{
std::cout << Base::value;
}
};
struct test_child : test_base
{
using ignored_friend_declaration_t = ignored_friend_declaration<test_base>;
friend ignored_friend_declaration_t;
static void test()
{
ignored_friend_declaration_t::bug();
}
};
int main()
{
test_child::test();
}
// ===================================
According to http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1873,
access to Base::value should be disallowed. Clang produces the following error
message: <source>:14:28: error: 'value' is a protected member of 'test_base'.
See also https://bugs.llvm.org/show_bug.cgi?id=46036
