std::is_trivially_default_constructible in C++ with Example
Last Updated :
12 Jun, 2020
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:
#include <iostream>
#include <type_traits>
using namespace std;
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;
cout << "int: "
<< is_trivially_default_constructible< int >::value
<< endl;
cout << "class A: "
<< is_trivially_default_constructible<A>::value
<< endl;
cout << "class B: "
<< is_trivially_default_constructible<B>::value
<< endl;
cout << "enum class C: "
<< is_trivially_default_constructible<C>::value
<< endl;
std::cout << "class D: "
<< is_trivially_default_constructible<D>::value
<< endl;
return 0;
}
|
Output:
int: true
class A: true
class B: false
enum class C: true
class D: false
Program 2:
#include <iostream>
#include <type_traits>
using namespace std;
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!" ;
}
};
int main()
{
cout << boolalpha;
cout << "Ex1 is default-constructible? "
<< is_trivially_default_constructible<Ex1>::value
<< '\n' ;
cout << "Ex1 is trivially default-constructible? "
<< is_trivially_default_constructible<Ex1>::value
<< '\n' ;
cout << "Ex2 is trivially default-constructible? "
<< is_trivially_default_constructible<Ex2>::value
<< '\n' ;
}
|
Output:
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/
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