Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::is_aggregate(3)	      C++ Standard Libary	  std::is_aggregate(3)

NAME
       std::is_aggregate - std::is_aggregate

Synopsis
	  Defined in header <type_traits>
	  template< class T >		   (since C++17)
	  struct is_aggregate;

	  Checks if T is an aggregate type. The	member constant	value is equal
       to true if T is
	  an aggregate type and	false otherwise.

	  The  behavior	is undefined if	std::remove_all_extents_t<T> is	an in-
       complete	type
	  other	than (possibly cv-qualified) void.

	  The behavior of a program that adds specializations for is_aggregate
       or
	  is_aggregate_v is undefined.

Template parameters
	  T - a	type to	check

	 Helper	variable template

	  template<		    class		  T		     >
       (since C++17)
	  inline constexpr bool	is_aggregate_v = is_aggregate<T>::value;

       Inherited from std::integral_constant

Member constants
	  value	   true	if T is	an aggregate type , 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>

Notes
	  Feature-test macro: __cpp_lib_is_aggregate

Example
       // Run this code

	#include <type_traits>
	#include <new>
	#include <utility>

	// constructs a	T at the uninitialized memory pointed to by p
	//  using  list-initialization for aggregates and non-list initializa-
       tion otherwise
	template<class T, class... Args>
	T* construct(T*	p, Args&&... args) {
	    if constexpr(std::is_aggregate_v<T>) {
		return	   ::new      (static_cast<void*>(p))	   T{std::for-
       ward<Args>(args)...};
	    }
	    else {
		return	    ::new      (static_cast<void*>(p))	   T(std::for-
       ward<Args>(args)...);
	    }
	}

	struct A { int x, y; };
	struct B { B(int, const	char*) { } };

	int main() {
	    std::aligned_union_t<1, A, B> storage;
	    [[maybe_unused]] A*	a =  construct(reinterpret_cast<A*>(&storage),
       1, 2);
	    [[maybe_unused]]  B* b = construct(reinterpret_cast<B*>(&storage),
       1, "hello");
	}

http://cppreference.com		  2022.07.31		  std::is_aggregate(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::is_aggregate&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help