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std::is_trivially_copyable

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

If T is a trivially copyable 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 cv-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

目次

Inherited from std::integral_constant

Member constants

value
[静的]
true T is a trivially copyable type もし、そうでなければfalse
Original:
true if T is a trivially copyable type , false otherwise
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(公共の静的メンバ定数)

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operator bool
boolにオブジェクトは、value返しに変換します
Original:
converts the object to bool, returns value
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(パブリックメンバ関数)

Member types

タイプ
Original:
Type
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Definition
value_type bool
type std::integral_constant<bool, value>

[編集] ノート

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.

[編集]

#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