std:: is_trivially_copyable

std::is_trivially_copyable is a UnaryTypeTrait .

If T is a trivially copyable type, provides the member constant value equal to true . For any other type, value is false .

If std:: remove_all_extents_t < T > is an incomplete type and not (possibly cv-qualified) void , the behavior is undefined.

If the program adds specializations for std::is_trivially_copyable or std::is_trivially_copyable_v , the behavior is undefined.

Template parameters

Helper variable template

Notes

Objects of trivially-copyable types that are not potentially-overlapping subobjects are the only C++ objects that may be safely copied with std::memcpy or serialized to/from binary files with std::ofstream::write() / std::ifstream::read() .

Example

#include <type_traits>
 
struct A { int m; };
static_assert(std::is_trivially_copyable_v<A> == true);
 
struct B { B(B const&) {} };
static_assert(std::is_trivially_copyable_v<B> == false);
 
struct C { virtual void foo(); };
static_assert(std::is_trivially_copyable_v<C> == false);
 
struct D
{
    int m;
 
    D(D const&) = default; // -> trivially copyable
    D(int x) : m(x + 1) {}
};
static_assert(std::is_trivially_copyable_v<D> == true);
 
int main() {}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also