std::is_trivially_copyable
Defined in header <type_traits>
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template< class T > struct is_trivially_copyable; |
(since C++11) | |
std::is_trivially_copyable
is a UnaryTypeTrait.
If T
is a trivially copyable type, provides the member constant value
equal to true. For any other type, value
is false.
If std::remove_all_extents_t<T> is an incomplete type and not (possibly cv-qualified) void, the behavior is undefined.
If the program adds specializations for std::is_trivially_copyable
or std::is_trivially_copyable_v
, the behavior is undefined.
Contents |
[edit] Template parameters
T | - | a type to check |
[edit] Helper variable template
template< class T > constexpr bool is_trivially_copyable_v = is_trivially_copyable<T>::value; |
(since C++17) | |
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) |
operator() (C++14) |
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 that are not potentially-overlapping subobjects 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().
[edit] Example
#include <type_traits> struct A { int m; }; static_assert(std::is_trivially_copyable_v<A> == true); struct B { B(B const&) {} }; static_assert(std::is_trivially_copyable_v<B> == false); struct C { virtual void foo(); }; static_assert(std::is_trivially_copyable_v<C> == false); struct D { int m; D(D const&) = default; // -> trivially copyable D(int x) : m(x + 1) {} }; static_assert(std::is_trivially_copyable_v<D> == true); int main() {}
[edit] 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 2015 | C++11 | T could be an array of incompleteclass type with unknown bound |
the behavior is undefined in this case |
[edit] See also
(C++11)(deprecated in C++26) |
checks if a type is trivial (class template) |