标准库头文件 <limits>

 

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技术规范

符号索引

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标准库头文件

语言支持
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <stdfloat> (C++23) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11) <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
概念
<concepts> (C++20)
诊断
<stdexcept> <stacktrace> (C++23)	<cassert>	<cerrno>	<system_error> (C++11)
内存管理
<memory>	<memory_resource> (C++17)	<scoped_allocator> (C++11)
元编程
<type_traits> (C++11)	<ratio> (C++11)
通用工具
<utility> <tuple> (C++11) <optional> (C++17) <variant> (C++17)	<any> (C++17) <debugging> (C++26) <expected> (C++23) <bitset>	<functional> <typeindex> (C++11) <execution> (C++17)	<charconv> (C++17) <format> (C++20) <bit> (C++20)
字符串
<string_view> (C++17) <string>	<cctype> <cwctype>	<cstring> <cwchar>	<cuchar> (C++11)
容器
<array> (C++11) <deque> <forward_list> (C++11) <list>	<vector> <map> <set> <unordered_map> (C++11)	<unordered_set> (C++11) <queue> <stack> <flat_map> (C++23)	<flat_set> (C++23) <span> (C++20) <mdspan> (C++23) <inplace_vector> (C++26)
迭代器
<iterator>
范围
<ranges> (C++20)	<generator> (C++23)
算法
<algorithm>	<numeric>
数值
<cfenv> (C++11) <complex>	<random> (C++11) <valarray>	<cmath> <linalg> (C++26)	<numbers> (C++20)
时间
<chrono> (C++11)	<ctime>
本地化
<locale>	<clocale>	<codecvt> (C++11/17/26*)	<text_encoding> (C++26)
输入/输出
<iosfwd> <iostream> <ios> <streambuf>	<istream> <ostream> <iomanip> <print> (C++23)	<sstream> <spanstream> (C++23) <fstream> <syncstream> (C++20)	<filesystem> (C++17) <cstdio> <cinttypes> (C++11) <strstream> (C++98/26*)
正则表达式
<regex> (C++11)
并发支持
<stop_token> (C++20) <thread> (C++11) <atomic> (C++11) <rcu> (C++26)	<stdatomic.h> (C++23) <mutex> (C++11) <shared_mutex> (C++14)	<condition_variable> (C++11)   <semaphore> (C++20) <latch> (C++20)	<barrier> (C++20) <future> (C++11) <hazard_pointer> (C++26)
C 兼容性
<cstdbool> (C++11/17/20*)   <ccomplex> (C++11/17/20*)	<ctgmath> (C++11/17/20*)	<cstdalign> (C++11/17/20*)	<ciso646> (直至 C++20)

 

此标头是 类型支持 库的一部分。

声明

numeric_limits	提供用于查询所有基本数值类型属性的接口 (类模板)
float_round_style	指示浮点舍入模式 (枚举)
float_denorm_style	指示浮点非规范化模式 (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 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 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

以下行为变更缺陷报告已追溯应用于先前发布的 C++ 标准。

DR	应用于	发布时的行为	正确行为
LWG 184	C++98	未提供特化 std::numeric_limits<bool> 的定义	已提供
LWG 559	C++98	cv 限定算术类型的 std::numeric_limits 特化 在概要中缺失	已添加