4. is_floating_point

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履歴 編集

class template
<type_traits>

std::is_floating_point(C++11)

namespace std {
  template <class T>
  struct is_floating_point;

  template <class T>
  inline constexpr bool is_floating_point_v = is_floating_point<T>::value; // C++17
}

概要

型Tが浮動小数点型かを調べる

効果

is_floating_pointは、型Tが浮動小数点型(cv修飾を許容する)であればtrue_typeから派生し、そうでなければfalse_typeから派生する。

例

#include <type_traits>

static_assert(std::is_floating_point<float>::value == true, "value == true, float is floating point");
static_assert(std::is_same<std::is_floating_point<float>::value_type, bool>::value, "value_type == bool");
static_assert(std::is_same<std::is_floating_point<float>::type, std::true_type>::value, "type == true_type");
static_assert(std::is_floating_point<float>() == true, "is_floating_point<float>() == true");

static_assert(std::is_floating_point<int>::value == false, "value == false, int is not floating point");
static_assert(std::is_same<std::is_floating_point<int>::value_type, bool>::value, "value_type == bool");
static_assert(std::is_same<std::is_floating_point<int>::type, std::false_type>::value, "type == false_type");
static_assert(std::is_floating_point<int>() == false, "is_floating_point<int>() == false");

static_assert(std::is_floating_point<double>::value == true, "double is floating point");
static_assert(std::is_floating_point<long double>::value == true, "long double is floating point");
static_assert(std::is_floating_point<const float>::value == true, "const float is floating point");
static_assert(std::is_floating_point<volatile double>::value == true, "volatile double is floating point");

static_assert(std::is_floating_point<unsigned>::value == false, "unsigned is not floating point");
static_assert(std::is_floating_point<float*>::value == false, "float* is not floating point");
static_assert(std::is_floating_point<double&>::value == false, "double& is not floating point");
static_assert(std::is_floating_point<long double[1]>::value == false, "long double[1] is not floating point");

int main(){}

出力

バージョン

言語

  • C++11

処理系

  • GCC: 4.3.4 ✅, 4.5.3 ✅, 4.6.1 ✅, 4.7.2 ✅
  • Visual C++: 2008 (std::tr1) ✅, 2010 ✅, 2012 ✅, 2013 ✅, 2015 ✅

備考

上の例でコンパイラによってはエラーになる。GCC 4.3.4, 4.5.3, Visual C++ 2010 は integral_constant が operator bool() を持っていないためエラーになる。

参照