NAME¶

std::is_trivially_copyable - std::is_trivially_copyable

Synopsis¶

Defined in header <type_traits>
template< class T > (since C++11)
struct 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¶

T - a type to check

Helper variable template

template< class T >
inline constexpr bool is_trivially_copyable_v = (since C++17)
is_trivially_copyable<T>::value;

Inherited from std::integral_constant

Member constants¶

value true if T is a trivially copyable type, false otherwise
[static] (public static member constant)

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (public member function)

Member types¶

Type Definition
value_type bool
type std::integral_constant<bool, value>

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¶

// Run this code

#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.

DR Applied to Behavior as published Correct behavior
LWG 2015 C++11 T could be an array of incomplete the behavior is
class type with unknown bound undefined in this case

See also¶

is_trivial checks if a type is trivial
(C++11) (class template)