class template
<type_traits>
std::is_trivially_default_constructible
template <class T> struct is_trivially_default_constructible;
Is trivially default constructible
Trait class that identifies whether T is a trivially default constructible type.
A trivially default constructible type is a type which can be trivially constructed without arguments or initialization values, either cv-qualified or not. This includes scalar types, trivially default constructible classes and arrays of such types.
A trivially default constructible class is a class (defined with class, struct or union) that:
- uses the implicitly defined default constructor.
- has no virtual members.
- has no non-static data members with brace- or equal- initializers.
- its base class and non-static data members (if any) are themselves also trivially default constructible types.
The is_trivially_default_constructible class inherits from integral_constant as being either true_type or false_type, depending on whether T is default constructible.
Template parameters
- T
- A complete type, or void (possible cv-qualified), or an array of unknown bound.
Member constants
Inherited from integral_constant:
| member constant | definition |
|---|
| value | either true or false |
Example
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// is_trivially_default_constructible example
#include <iostream>
#include <type_traits>
struct A { };
struct B { B(){} };
struct C { virtual void fn() {} };
int main() {
std::cout << std::boolalpha;
std::cout << "is_trivially_default_constructible:" << std::endl;
std::cout << "int: " << std::is_trivially_default_constructible<int>::value << std::endl;
std::cout << "A: " << std::is_trivially_default_constructible<A>::value << std::endl;
std::cout << "B: " << std::is_trivially_default_constructible<B>::value << std::endl;
std::cout << "C: " << std::is_trivially_default_constructible<C>::value << std::endl;
return 0;
}
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Output:
is_trivially_default_constructible:
int: true
A: true
B: false
C: false
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