https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116469
--- Comment #3 from Arvid Jonasson <jonassonarvid02 at gmail dot com> ---
Modified Example 2 with non-aggregate types:
------------------------------------------------------------------------------
#include <iostream>
#include <utility>
#include <vector>
template<unsigned int N>
struct Inner {
Inner() {}
unsigned char arr[N];
};
struct Outer1 {
template<unsigned int N>
class Outer {
int dummy;
Inner<N> inner;
public:
Inner<N>& getInner() { return inner; }
};
};
struct Outer2 {
template<unsigned int N>
class Outer {
Inner<N> inner;
public:
Inner<N>& getInner() { return inner; }
};
};
struct Outer3 {
template<unsigned int N>
class Outer {
Inner<N> inner;
int dummy;
public:
Inner<N>& getInner() { return inner; }
};
};
template<typename T, unsigned int N>
bool isZeroInit() {
for(int i = 0; i < 2; i++) {
typename T::template Outer<N> outer{};
for(auto &c : outer.getInner().arr) {
if(c != 0) {
return false;
}
c = 1;
}
}
return true;
}
template <typename T, unsigned int N>
auto checkZeroInit(std::vector<bool> v, std::integer_sequence<unsigned int, N>)
{
if constexpr (N != 0)
v.push_back(isZeroInit<T, N>());
return v;
}
template <typename T, unsigned int N, unsigned int... M>
auto checkZeroInit(std::vector<bool> v, std::integer_sequence<unsigned int, N,
M...>) {
if constexpr (N != 0)
v.push_back(isZeroInit<T, N>());
return checkZeroInit<T>(std::move(v), std::integer_sequence<unsigned int,
M...>{});
}
int main() {
auto v = checkZeroInit<Outer1>(std::vector<bool>{},
std::make_integer_sequence<unsigned int, 300>{});
std::cout << "Outer1: ";
for(auto b : v)
std::cout << b;
std::cout << std::endl;
v = checkZeroInit<Outer2>(std::vector<bool>{},
std::make_integer_sequence<unsigned int, 300>{});
std::cout << "Outer2: ";
for(auto b : v)
std::cout << b;
std::cout << std::endl;
v = checkZeroInit<Outer3>(std::vector<bool>{},
std::make_integer_sequence<unsigned int, 300>{});
std::cout << "Outer3: ";
for(auto b : v)
std::cout << b;
std::cout << std::endl;
return 0;
}
------------------------------------------------------------------------------
Output:
arvidjonasson@Arvids-MacBook-Air ~/testZeroInit
% g++-14 -O3 -std=c++17 -Wall -Wextra example2.cpp -o example2.out
--[ lots of -Wmaybe-uninitialized warnings ]--
inlined from 'int main()' at example2.cpp:83:30:
example2.cpp:46:18: warning:
'outer.Outer3::Outer<17>::inner.Inner<17>::arr[16]' may be used uninitialized
[-Wmaybe-uninitialized]
46 | if(c != 0) {
| ~~^~~~
example2.cpp: In function 'int main()':
example2.cpp:44:39: note: 'outer' declared here
44 | typename T::template Outer<N> outer{};
|
arvidjonasson@Arvids-MacBook-Air ~/testZeroInit
% ./example2.out
Outer1:
11010000000000000110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011101110111011111111111111111111111111111111111111111111111
Outer2:
11111111111111101000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Outer3:
11111111111111111000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000011111111111111111111111111111111111111111111111
------------------------------------------------------------------------------
Expected behaviour:
Program should output all 1's since all objects should be zero initialized.
Actual behaviour:
Program doesn't output all 1's since all objects are not zero initialized.
