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

 

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Type traits
Type categories is_void (C++11) is_null_pointer (C++14)   is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11) is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11)   is_fundamental (C++11) is_arithmetic (C++11) is_reference (C++11) is_lvalue_reference (C++11) is_rvalue_reference (C++11) is_member_pointer (C++11) is_member_object_pointer (C++11) is_member_function_pointer (C++11) Type properties is_const (C++11) is_volatile (C++11) is_empty (C++11) is_polymorphic (C++11) is_final (C++14) is_abstract (C++11) is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (C++11) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11)(until C++20*) is_pod (C++11)(deprecated in C++20) is_signed (C++11) is_unsigned (C++11) is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17) Type trait constants integral_constantbool_constanttrue_typefalse_type (C++11)(C++17)(C++11)(C++11) Metafunctions conjunction (C++17) disjunction (C++17) negation (C++17)	Supported operations is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11) is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11) is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11) is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11) is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11) is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11) has_virtual_destructor (C++11) is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) Relationships and property queries is_same (C++11) is_convertibleis_nothrow_convertible (C++11)(C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)   is_corresponding_member (C++20) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) is_base_of (C++11) is_virtual_base_of (C++26) alignment_of (C++11) rank (C++11) extent (C++11) is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) Type modifications remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11) remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11) Type transformations aligned_storage (C++11)(deprecated in C++23) aligned_union (C++11)(deprecated in C++23) decay (C++11) remove_cvref (C++20) enable_if (C++11) void_t (C++17) conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) result_ofinvoke_result (C++11)(until C++20*)(C++17) type_identity (C++20)
Compile-time rational arithmetic
Compile-time integer sequences
integer_sequence (C++14)

 

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

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

Helper variable templates

template< class T > inline constexpr bool is_copy_constructible_v =     is_copy_constructible<T>::value;		(since C++17)
template< class T > inline constexpr bool is_trivially_copy_constructible_v =     is_trivially_copy_constructible<T>::value;		(since C++17)
template< class T > inline constexpr bool is_nothrow_copy_constructible_v =     is_nothrow_copy_constructible<T>::value;		(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

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)
operator() (C++14)	returns value (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&) {}; // cannot bind const, hence not a copy-constructible
};
static_assert(!std::is_copy_constructible_v<S4>);
 
int main() {}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2196	C++11	the behavior was unclear if const T& cannot be formed	the value produced is false in this case

See also

is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11)	checks if a type has a constructor for specific arguments (class template)
is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11)	checks if a type has a default constructor (class template)
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)	checks if a type can be constructed from an rvalue reference (class template)
copy_constructible (C++20)	specifies that an object of a type can be copy constructed and move constructed (concept)