The std::is_trivially_default_constructible template of C++ STL is present in the <type_traits> header file. The std::is_trivially_default_constructible template of C++ STL is used to check whether T is trivially default constructible type or not. It return the boolean value true if T is trivially default constructible type, otherwise return false.
Header File:
#include<type_traits>
Template Class:
template< class T > struct is_default_constructible;
Syntax:
std::is_trivially_default_constructible<T>::value
Parameter: The template std::is_trivially_default_constructible accepts a single parameter T(Trait class) to check whether T is trivially default constructible type or not.
Return Value: The template std::is_trivially_default_constructible returns a boolean variable as shown below:
- True: If the type T is a trivially default constructible.
- False: If the type T is not a trivially default constructible.
Below is the program to demonstrate std::is_trivially_default_constructible in C++:
Program 1:
// C++ program to demonstrate // std::is_trivially_default_constructible #include <iostream> #include <type_traits> using namespace std;
// Declaration of classes class A {
}; class B {
B() {}
}; enum class C : int { x,
y,
z };
class D {
int v1;
double v2;
public :
D( int n)
: v1(n), v2()
{
}
D( int n, double f)
noexcept : v1(n), v2(f) {}
}; int main()
{ cout << boolalpha;
// Check if int is trivially
// default constructible or not
cout << "int: "
<< is_trivially_default_constructible< int >::value
<< endl;
// Check if class A is trivially
// default constructible or not
cout << "class A: "
<< is_trivially_default_constructible<A>::value
<< endl;
// Check if class B is trivially
// default constructible or not
cout << "class B: "
<< is_trivially_default_constructible<B>::value
<< endl;
// Check if enum class C is trivially
// default constructible or not
cout << "enum class C: "
<< is_trivially_default_constructible<C>::value
<< endl;
// Check if class D is trivially
// default constructible or not
std::cout << "class D: "
<< is_trivially_default_constructible<D>::value
<< endl;
return 0;
} |
int: true class A: true class B: false enum class C: true class D: false
Program 2:
// C++ program to demonstrate // std::is_trivially_default_constructible #include <iostream> #include <type_traits> using namespace std;
// Declare structures struct Ex1 {
Ex1() {}
Ex1(Ex1&&)
{
cout << "Throwing move constructor!" ;
}
Ex1( const Ex1&)
{
cout << "Throwing copy constructor!" ;
}
}; struct Ex2 {
Ex2() {}
Ex2(Ex2&&) noexcept
{
cout << "Non-throwing move constructor!" ;
}
Ex2( const Ex2&) noexcept
{
cout << "Non-throwing copy constructor!" ;
}
}; // Driver Code int main()
{ cout << boolalpha;
// Check if struct Ex1 is default
// constructible or not
cout << "Ex1 is default-constructible? "
<< is_trivially_default_constructible<Ex1>::value
<< '\n' ;
// Check if struct Ex1 is trivially
// defaultconstructible or not
cout << "Ex1 is trivially default-constructible? "
<< is_trivially_default_constructible<Ex1>::value
<< '\n' ;
// Check if struct Ex2 is trivially
// defaultconstructible or not
cout << "Ex2 is trivially default-constructible? "
<< is_trivially_default_constructible<Ex2>::value
<< '\n' ;
} |
Ex1 is default-constructible? false Ex1 is trivially default-constructible? false Ex2 is trivially default-constructible? false
Reference: http://www.cplusplus.com/reference/type_traits/is_trivially_default_constructible/