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std::is_trivially_copyable

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< cpp‎ | types
 
 
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is_trivially_copyable
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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.

Contents

[edit] Template parameters

T - a type to check

[edit] 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>

[edit] 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().

[edit] Example

#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

[edit] See also

checks if a type is trivial
(class template) [edit]