std::is_trivially_copyable

template< class T >
struct is_trivially_copyable;

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).

A trivially copyable class is a class that.

1. Has no non-trivial copy constructors (this also requires no virtual functions or virtual bases)
2. Has no non-trivial move constructors
3. Has no non-trivial copy assignment operators
4. Has no non-trivial move assignment operators
5. Has a trivial destructor

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

Template parameters

Helper variable template

template< class T >
constexpr bool is_trivially_copyable_v = is_trivially_copyable<T>::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

#include <iostream>
#include <type_traits>
 
struct A {
    int m;
};
 
struct B {
    B(const B&) {}
};
 
struct C {
    virtual void foo();
};
 
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';
}

true
false
false

See also