Defined in header <type_traits> | ||
---|---|---|
template< class T > struct is_trivially_copyable; | (since C++11) |
If T
is a TriviallyCopyable type, provides the member constant value
equal true
. For any other type, value
is false
.
The only trivially copyable types are scalar types, trivially copyable classes, and arrays of such types/classes (possibly const-qualified, but not volatile-qualified).
The behavior is undefined if std::remove_all_extents_t<T>
is an incomplete type and not (possibly cv-qualified) void
.
T | - | a type to check |
template< class T > inline constexpr bool is_trivially_copyable_v = is_trivially_copyable<T>::value; | (since C++17) |
value
[static] | true if T is a trivially copyable type , false otherwise (public static member constant) |
operator bool | converts the object to bool , returns value (public member function) |
operator()
(C++14) | returns value (public member function) |
Type | Definition |
---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
Objects of trivially-copyable types 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()
.
In general, for any trivially copyable type T
and an object obj1
of T
, the underlying bytes of obj1
can be copied (e.g. by means of std::memcpy
or std::memmove
) into an array of char
, unsigned char
or std::byte
or into obj2
, a distinct object of T
. Neither obj1
nor obj2
may be a potentially-overlapping subobject.
If the underlying bytes of obj1
is copied into such an array, and then the resulting content is copied back into obj1
, obj1
will hold its original value. If the underlying bytes of obj1
are copied into obj2
, obj2
will hold obj1
's value.
#include <iostream> #include <type_traits> struct A { int m; }; struct B { B(B const&) {} }; struct C { virtual void foo(); }; struct D { int m; D(D const&) = default; // -> trivially copyable D(int x): m(x+1) {} }; int main() { std::cout << std::boolalpha; std::cout << std::is_trivially_copyable<A>::value << '\n'; std::cout << std::is_trivially_copyable<B>::value << '\n'; std::cout << std::is_trivially_copyable<C>::value << '\n'; std::cout << std::is_trivially_copyable<D>::value << '\n'; }
Output:
true false false true
(C++11) | checks if a type is trivial (class template) |
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