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# std::is_trivially_copyable

From cppreference.com
< cpp‎ | types

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 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

## 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)

### 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

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

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