# 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 an UnaryTypeTrait.

If `T` is a trivially copyable type, the base characteristic is std::true_type. For any other type, the base characteristic is std::false_type.

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

The behavior of a program that adds specializations for `std::is_trivially_copyable` or `std::is_trivially_copyable_v` (since C++17) is undefined.

### Template parameters

T | - | a type to check

### Helper variable template

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

## 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>

### 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 class type with unknown bound | the behavior is undefined in this case

### See also

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

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