NAME¶

std::is_copy_constructible,std::is_trivially_copy_constructible, - std::is_copy_constructible,std::is_trivially_copy_constructible,

Synopsis¶

Defined in header <type_traits>
template< class T > (1) (since C++11)
struct is_copy_constructible;
template< class T > (2) (since C++11)
struct is_trivially_copy_constructible;
template< class T > (3) (since C++11)
struct is_nothrow_copy_constructible;

The value of the member constant value
Type trait T is a referenceable type T is not a
referenceable type
(1) std::is_constructible<T, const T&>::value
(2) std::is_trivially_constructible<T, const false
T&>::value
(3) std::is_nothrow_constructible<T, const T&>::value

If T is not a complete type, (possibly cv-qualified) void, or an array of unknown
bound, the behavior is undefined.

If an instantiation of a template above depends, directly or indirectly, on an
incomplete type, and that instantiation could yield a different result if that type
were hypothetically completed, the behavior is undefined.

If the program adds specializations for any of the templates described on this page,
the behavior is undefined.

Member constants¶

value true if T is copy-constructible, false otherwise
[static] (public static member constant)

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (public member function)

Member types¶

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

Possible implementation¶

template<class T>
struct is_copy_constructible :
std::is_constructible<T, typename std::add_lvalue_reference<
typename std::add_const<T>::type>::type> {};

template<class T>
struct is_trivially_copy_constructible :
std::is_trivially_constructible<T, typename std::add_lvalue_reference<
typename std::add_const<T>::type>::type> {};

template<class T>
struct is_nothrow_copy_constructible :
std::is_nothrow_constructible<T, typename std::add_lvalue_reference<
typename std::add_const<T>::type>::type> {};

Notes¶

In many implementations, is_nothrow_copy_constructible also checks if the destructor
throws because it is effectively noexcept(T(arg)). Same applies to
is_trivially_copy_constructible, which, in these implementations, also requires that
the destructor is trivial: GCC bug 51452, LWG issue 2116.

Example¶

// Run this code

#include <string>
#include <type_traits>

struct S1
{
std::string str; // member has a non-trivial copy constructor
};
static_assert(std::is_copy_constructible_v<S1>);
static_assert(!std::is_trivially_copy_constructible_v<S1>);

struct S2
{
int n;
S2(const S2&) = default; // trivial and non-throwing
};
static_assert(std::is_trivially_copy_constructible_v<S2>);
static_assert(std::is_nothrow_copy_constructible_v<S2>);

struct S3
{
S3(const S3&) = delete; // explicitly deleted
};
static_assert(!std::is_copy_constructible_v<S3>);

struct S4
{
S4(S4&) {}; // can't bind const, hence not a copy-constructible
};
static_assert(!std::is_copy_constructible_v<S4>);

int main() {}

See also¶

is_constructible
is_trivially_constructible checks if a type has a constructor for specific
is_nothrow_constructible arguments
(C++11) (class template)
(C++11)
(C++11)
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible checks if a type has a default constructor
(C++11) (class template)
(C++11)
(C++11)
is_move_constructible
is_trivially_move_constructible checks if a type can be constructed from an
is_nothrow_move_constructible rvalue reference
(C++11) (class template)
(C++11)
(C++11)
copy_constructible specifies that an object of a type can be copy
(C++20) constructed and move constructed
(concept)