4. is_floating_point

    • Class / Function / Type

      std::

    • Header file

      <>

    • Other / All

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    class template
    <type_traits>

    std::is_floating_point

    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