std::is_copy_constructible, std::is_trivially_copy_constructible, std::is_nothrow_copy_constructible

From Cppreference

Defined in header `<type_traits>`

template< class T > struct is_copy_constructible;	(1)	(C++11 feature)

template< class T > struct is_trivially_copy_constructible;	(2)	(C++11 feature)

template< class T > struct is_nothrow_copy_constructible;	(3)	(C++11 feature)

1) If the constructor expression T(arg); is well-formed for arg of type const T& (that is, T is a scalar or reference or a class with an accessible copy constructor), provides the member constant value equal true. For any other type, value is false.

2) same as 1), but the copy constructor expression does not call any operation that is not trivial.

3) same as 1), but the copy constructor expression is noexcept.

Inherited from std::integral_constant

Member constants


`value`	true if `T` is copy-constructible , 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] Equivalent definition

template<class T>
struct is_copy_constructible :
    std::is_constructible<T, const typename std::add_lvalue_reference<T>::type> {};
 
template<class T>
struct is_trivially_copy_constructible :
    std::is_trivially_constructible<T, const typename std::add_lvalue_reference<T>::type> {};
 
template<class T>
struct is_nothrow_copy_constructible :
    std::is_nothrow_constructible<T, const typename std::add_lvalue_reference<T>::type> {};

[edit] Example

#include <iostream>
#include <type_traits>
 
struct Ex1 {
    std::string str; // member has a non-trivial copy ctor
};
struct Ex2 {
    int n;
    Ex2(const Ex2&) = default; // trivial and non-throwing
};
 
int main() {
    std::cout << std::boolalpha << "Ex1 is copy-constructible? "
              << std::is_copy_constructible<Ex1>::value << '\n'
              << "Ex1 is trivially copy-constructible? "
              << std::is_trivially_copy_constructible<Ex1>::value << '\n'
              << "Ex2 is trivially copy-constructible? "
              << std::is_trivially_copy_constructible<Ex2>::value << '\n'
              << "Ex2 is nothrow copy-constructible? "
              << std::is_nothrow_copy_constructible<Ex2>::value << '\n';
}

Output:

Ex1 is copy-constructible? true
Ex1 is trivially copy-constructible? false
Ex2 is trivially copy-constructible? true
Ex2 is nothrow copy-constructible? true

[edit] See also

is_constructible is_trivially_constructible is_nothrow_constructible (C++11)
(C++11)
(C++11)

checks if a type has a constructor for specific arguments
(class template)

is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11)
(C++11)
(C++11)

checks if a type has a default constructor
(class template)

is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11)
(C++11)
(C++11)

checks if a type has a move constructor
(class template)