<type_traits>

類模板
<type_traits>

std::is_union

template <class T> struct is_union;
Is union

Trait class that identifies whether T is a union type.

它繼承自 integral_constant,其值為 true_typefalse_type

模板引數

T
一個型別。

成員型別

Inherited from integral_constant
成員型別定義
value_typebool
型別true_type 或 false_type

成員常量

Inherited from integral_constant
成員常量定義
trueorfalse

成員函式

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;
}

輸出
is_union:
int: false
A: true
B: false


另見