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std::is_trivially_copyable

From cppreference.com
< cpp‎ | types
 
 
 
Type support
Type properties
(C++11)
(C++11)
(C++11)
(C++14)
(C++11)
is_trivially_copyable
(C++11)
(C++11)
Type trait constants
Metafunctions
(C++17)
Supported operations
Relationships and property queries
(C++11)
(C++11)
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Type modifications
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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.

Contents

[edit] Template parameters

T - a type to check

[edit] 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>

[edit] 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.

[edit] 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';
}

Output:

true
false
false

[edit] See also

checks if a type is trivial
(class template) [edit]
variable template alias of std::is_trivially_copyable::value
(variable template) [edit]