std::is_trivially_copyable - cppreference.com (original) (raw)

| | | | | ---------------------------------------------------- | | ------------- | | 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

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Notes
  • 3.5 Example
  • 3.6 Defect reports
  • 3.7 See also

[edit] Template parameters

[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

| | true if T is a trivially copyable type, false otherwise (public static member constant) | | ------------------------------------------------------------------------------------------ |

Member functions

| | converts the object to bool, returns value (public member function) | | ---------------------------------------------------------------------- | | | returns value (public member function) |

Member types

[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   struct A { int m; }; static_assert(std::is_trivially_copyable_v == true);   struct B { B(B const&) {} }; static_assert(std::is_trivially_copyable_v == false);   struct C { virtual void foo(); }; static_assert(std::is_trivially_copyable_v == false);   struct D { int m;   D(D const&) = default; // -> trivially copyable D(int x) : m(x + 1) {} }; static_assert(std::is_trivially_copyable_v == true);   int main() {}

[edit] Defect reports

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

[edit] See also