RetroSearch Browse

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../types/is_default_constructible.html below:

std::is_default_constructible, std::is_trivially_default_constructible, std::is_nothrow_default_constructible - cppreference.com

template< class T > struct is_default_constructible;

(1) (since C++11)

template< class T > struct is_trivially_default_constructible;

(2) (since C++11)

template< class T > struct is_nothrow_default_constructible;

(3) (since C++11)

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.

[edit] Helper variable templates template< class T > inline constexpr bool is_default_constructible_v = is_default_constructible<T>::value; (since C++17) template< class T > inline constexpr bool is_trivially_default_constructible_v = is_trivially_default_constructible<T>::value; (since C++17) template< class T > inline constexpr bool is_nothrow_default_constructible_v = is_nothrow_default_constructible<T>::value; (since C++17) Inherited from std::integral_constant Member constants true if T is default-constructible, 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] Possible implementation [edit] Notes

In many implementations, std::is_nothrow_default_constructible also checks if the destructor throws because it is effectively noexcept(T()). Same applies to std::is_trivially_default_constructible, which, in these implementations, also requires that the destructor is trivial: GCC bug 51452, LWG issue 2116.

std::is_default_constructible<T> does not test that T x; would compile; it attempts direct-initialization with an empty argument list (see std::is_constructible). Thus, std::is_default_constructible_v<const int> and std::is_default_constructible_v<const int[10]> are true.

[edit] Example

#include <string>
#include <type_traits>
 
struct S1
{
    std::string str; // member has a non-trivial default constructor
};
static_assert(std::is_default_constructible_v<S1> == true);
static_assert(std::is_trivially_default_constructible_v<S1> == false);
 
struct S2
{
    int n;
    S2() = default; // trivial and non-throwing
};
static_assert(std::is_trivially_default_constructible_v<S2> == true);
static_assert(std::is_nothrow_default_constructible_v<S2> == true);
 
int main() {}

[edit] See also

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4