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Standard library header <limits>

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C++
Standard library headers

此头文件是 类型支持 库的组成部分。

目录

声明

提供查询所有基础数值类型属性的接口
(类模板)
表示浮点数舍入模式
(枚举)
表示浮点数非规范化模式
(枚举)

概要 

namespace std {
    enum float_round_style;
    enum float_denorm_style;
    template<class T> class numeric_limits;
    template<class T> class numeric_limits<const T>;
    template<class T> class numeric_limits<volatile T>;
    template<class T> class numeric_limits<const volatile T>;
    template<> class numeric_limits<bool>;
    template<> class numeric_limits<char>;
    template<> class numeric_limits<signed char>;
    template<> class numeric_limits<unsigned char>;
    template<> class numeric_limits<char8_t>;
    template<> class numeric_limits<char16_t>;
    template<> class numeric_limits<char32_t>;
    template<> class numeric_limits<wchar_t>;
    template<> class numeric_limits<short>;
    template<> class numeric_limits<int>;
    template<> class numeric_limits<long>;
    template<> class numeric_limits<long long>;
    template<> class numeric_limits<unsigned short>;
    template<> class numeric_limits<unsigned int>;
    template<> class numeric_limits<unsigned long>;
    template<> class numeric_limits<unsigned long long>;
    template<> class numeric_limits<float>;
    template<> class numeric_limits<double>;
    template<> class numeric_limits<long double>;
}

枚举类型 std::float_round_style 

namespace std {
    enum float_round_style {
        round_indeterminate       = -1,
        round_toward_zero         =  0,
        round_to_nearest          =  1,
        round_toward_infinity     =  2,
        round_toward_neg_infinity =  3,
    };
}

枚举类型 std::float_denorm_style 

namespace std {
    enum float_denorm_style {
        denorm_indeterminate = -1,
        denorm_absent        =  0,
        denorm_present       =  1
    };
}

类模板 std::numeric_limits 

template<class T> class numeric_limits {
public:
    static constexpr bool is_specialized = false;
    static constexpr T min() noexcept { return T(); }
    static constexpr T max() noexcept { return T(); }
    static constexpr T lowest() noexcept { return T(); }
    static constexpr int digits = 0;
    static constexpr int digits10 = 0;
    static constexpr int max_digits10 = 0;
    static constexpr bool is_signed = false;
    static constexpr bool is_integer = false;
    static constexpr bool is_exact = false;
    static constexpr int radix = 0;
    static constexpr T epsilon() noexcept { return T(); }
    static constexpr T round_error() noexcept { return T(); }
    static constexpr int min_exponent = 0;
    static constexpr int min_exponent10 = 0;
    static constexpr int max_exponent = 0;
    static constexpr int max_exponent10 = 0;
    static constexpr bool has_infinity = false;
    static constexpr bool has_quiet_NaN = false;
    static constexpr bool has_signaling_NaN = false;
    static constexpr float_denorm_style has_denorm = denorm_absent;
    static constexpr bool has_denorm_loss = false;
    static constexpr T infinity() noexcept { return T(); }
    static constexpr T quiet_NaN() noexcept { return T(); }
    static constexpr T signaling_NaN() noexcept { return T(); }
    static constexpr T denorm_min() noexcept { return T(); }
    static constexpr bool is_iec559 = false;
    static constexpr bool is_bounded = false;
    static constexpr bool is_modulo = false;
    static constexpr bool traps = false;
    static constexpr bool tinyness_before = false;
    static constexpr float_round_style round_style = round_toward_zero;
};

特化 std:: numeric_limits < bool > 

template<> class numeric_limits<bool> {
public:
    static constexpr bool is_specialized = true;
    static constexpr bool min() noexcept { return false; }
    static constexpr bool max() noexcept { return true; }
    static constexpr bool lowest() noexcept { return false; }
    static constexpr int digits = 1;
    static constexpr int digits10 = 0;
    static constexpr int max_digits10 = 0;
    static constexpr bool is_signed = false;
    static constexpr bool is_integer = true;
    static constexpr bool is_exact = true;
    static constexpr int radix = 2;
    static constexpr bool epsilon() noexcept { return 0; }
    static constexpr bool round_error() noexcept { return 0; }
    static constexpr int min_exponent = 0;
    static constexpr int min_exponent10 = 0;
    static constexpr int max_exponent = 0;
    static constexpr int max_exponent10 = 0;
    static constexpr bool has_infinity = false;
    static constexpr bool has_quiet_NaN = false;
    static constexpr bool has_signaling_NaN = false;
    static constexpr float_denorm_style has_denorm = denorm_absent;
    static constexpr bool has_denorm_loss = false;
    static constexpr bool infinity() noexcept { return 0; }
    static constexpr bool quiet_NaN() noexcept { return 0; }
    static constexpr bool signaling_NaN() noexcept { return 0; }
    static constexpr bool denorm_min() noexcept { return 0; }
    static constexpr bool is_iec559 = false;
    static constexpr bool is_bounded = true;
    static constexpr bool is_modulo = false;
    static constexpr bool traps = false;
    static constexpr bool tinyness_before = false;
    static constexpr float_round_style round_style = round_toward_zero;
};

缺陷报告

下列行为变更缺陷报告被追溯应用于先前发布的 C++ 标准。

缺陷报告 适用范围 发布时行为 正确行为
LWG 184 C++98 未提供特化版本 std:: numeric_limits < bool > 的定义 已提供
LWG 559 C++98 在概要说明中缺少 cv 限定
算术类型的 std::numeric_limits 特化 		已添加