<type_traits>

类模板
<type_traits>

std::is_trivial

template <class T> struct is_trivial;
Is trivial type

Trait class that identifies whether T is a trivial type.

A trivial type is a type whose storage is contiguous (trivially copyable) and which only supports static default initialization (trivially default constructible), either cv-qualified or not. It includes scalar types, trivial classes and arrays of any such types.

A trivial class is a class (defined with, structor联合体) that is both trivially default constructible and trivially copyable, which implies that
  • uses the implicitly defined default, copy and move constructors, copy and move assignments, and destructor.
  • 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 trivial types.

is_trivialinherits from integral_constant as being either true_type or false_type, depending on whetherTis a trivial type.

模板参数

T
一个完整类型,或者void(possible cv-qualified), or an array of unknown bound of a complete element type.

成员类型

Inherited from integral_constant
成员类型定义
value_typebool
类型true_type 或 false_type

成员常量

Inherited from integral_constant
成员常量定义
trueorfalse

成员函数

Inherited from integral_constant

示例

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// is_trivial example
#include <iostream>
#include <type_traits>

class A {};
class B { B() {} };
class C : B {};
class D { virtual void fn() {} };

int main() {
  std::cout << std::boolalpha;
  std::cout << "is_trivial:" << std::endl;
  std::cout << "int: " << std::is_trivial<int>::value << std::endl;
  std::cout << "A: " << std::is_trivial<A>::value << std::endl;
  std::cout << "B: " << std::is_trivial<B>::value << std::endl;
  std::cout << "C: " << std::is_trivial<C>::value << std::endl;
  std::cout << "D: " << std::is_trivial<D>::value << std::endl;
  return 0;
}

输出
is_trivial:
int: true
A: true
B: false
C: false
D: false


另见