https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107361
Bug ID: 107361
Summary: Why does -Wclass-memaccess require trivial types,
instead of trivially-copyable types?
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: carlosgalvezp at gmail dot com
Target Milestone: ---
I find -Wclass-memaccess warns on this kind of code:
#include <cstring>
struct Foo
{
int x{};
char y{};
int z{};
};
int main()
{
Foo a;
std::memset(&a, 0, sizeof(a));
}
All because Foo has default member initializers, making it a non-trivial type.
It's still trivially-copyable, which is the requirement for std::memset.
Therefore I ask: why is the warning stricter than it needs to be?
Making sure structs are initialized is defensive programming, and consistent
with coding guidelines that require classes to initialize their data members.
Also, there are cases where we cannot use the C++ initialization (Foo a = {};).
For example, this class has implicit padding, and the C++ initialization will
not initialize that. This is a problem for serializer/deserializer type of code
(copying/reading uninitialized padding bytes, valgrind will complain).
