<type_traits>

类模板
<type_traits>

std::is_union

template <class T> struct is_union;
Is union

Trait class that identifies whether T is a union type.

它继承自 integral_constant,其值为 true_typefalse_type

模板参数

T
一个类型。

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_union example
#include <iostream>
#include <type_traits>

union A { int i; float f; };        // named union
struct B {
  union { int foo; float bar; };    // anonymous member union
};

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

输出
is_union:
int: false
A: true
B: false


另见