类模板
<type_traits>
std::is_trivially_default_constructible
template <class T> struct is_trivially_default_constructible;
Is trivially default constructible
用于识别Tis 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类, structor联合体定义）
- uses the implicitly defined default constructor.
- 没有虚成员。
- 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.
要放回的字符的is_trivially_default_constructible类继承自integral_constant，其值为true_type或false_type，取决于T是否可默认构造。
模板参数
- T
- 一个完整类型，或者void（可能带 cv 限定），或者一个未知边界的数组。
示例
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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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输出
is_trivially_default_constructible:
int: true
A: true
B: false
C: false
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