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std::is_trivially_copyable

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

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.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

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

Inherited from std::integral_constant

Member constants

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

Member functions

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

Member types

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

[edit] 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().

[edit] 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() {}

[edit] 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
class type with unknown bound 		the behavior is
undefined in this case

[edit] See also

(C++11)
 checks if a type is trivial
(class template) [edit]
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