std::is_trivially_copyable

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

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

The only trivially copyable types are scalar types, trivially copyable classes, and arrays of such types/classes (possibly const-qualified, but not volatile-qualified).

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

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 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(). In general, a trivially copyable type is any type for which the underlying bytes can be copied to an array of char or unsigned char and into a new object of the same type, and the resulting object would have the same value as the original.

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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