std::is_trivially_copyable

 

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type_info type_index (C++11)	bad_typeid bad_cast

 

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

If T is a Template:concept 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 > 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(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';
}

Output:

true
false
false

See also

is_trivial (C++11)	checks if a type is trivial (class template)
std::experimental::is_trivially_copyable_v (library fundamentals TS)	variable template alias of std::is_trivially_copyable::value (variable template)