std::is_trivially_copyable

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

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

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

The behavior of a program that adds specializations for is_trivially_copyable or 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 <iostream>
#include <type_traits>
 
struct A
{
    int m;
};
 
struct B
{
    B(B const&) {}
};
 
struct C
{
    virtual void foo();
};
 
struct D
{
    int m;
 
    D(D const&) = default; // -> trivially copyable
    D(int x): m(x+1) {}
};
 
int main()
{
    std::cout << std::boolalpha;
    std::cout << std::is_trivially_copyable<A>::value << '\n';
    std::cout << std::is_trivially_copyable<B>::value << '\n';
    std::cout << std::is_trivially_copyable<C>::value << '\n';
    std::cout << std::is_trivially_copyable<D>::value << '\n';
}

Output:

true
false
false
true

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