C++标准模板（STL）- 类型支持 (数值极限，epsilon，round_error，infinity)
数值极限
提供查询所有基础数值类型的性质的接口
定义于头文件
template< class T > class numeric_limits;numeric_limits 类模板提供查询各种算术类型属性的标准化方式（例如 int 类型的最大可能值是 std::numeric_limits
返回 1.0 与给定类型的下个可表示值的差
std::numeric_limits::epsilon | static T epsilon() throw(); |
(C++11 前) | |
| static constexpr T epsilon() noexcept; |
(C++11 起) |
返回机器 epsilon ，即 1.0 与浮点类型 T 的下个可表示值的差。它仅若 std::numeric_limits
返回值
T |
std::numeric_limits |
| /* non-specialized */ | T() |
| bool | false |
| char | 0 |
| signed char | 0 |
| unsigned char | 0 |
| wchar_t | 0 |
| char8_t | 0 |
| char16_t | 0 |
| char32_t | 0 |
| short | 0 |
| unsigned short | 0 |
| int | 0 |
| unsigned int | 0 |
| long | 0 |
| unsigned long | 0 |
| long long | 0 |
| unsigned long long | 0 |
| float | FLT_EPSILON |
| double | DBL_EPSILON |
| long double | LDBL_EPSILON |
调用示例
#include
#include
#include
#include
#include
struct SName
{
};
//偏特化
struct SPartSpec
{
};
namespace std
{
template<>
struct numeric_limits
{
static _GLIBCXX_USE_CONSTEXPR bool is_specialized = true;
static _GLIBCXX_USE_CONSTEXPR bool is_signed = true;
static _GLIBCXX_USE_CONSTEXPR bool is_integer = true;
static _GLIBCXX_USE_CONSTEXPR bool is_exact = true;
static _GLIBCXX_USE_CONSTEXPR bool has_infinity = true;
static _GLIBCXX_USE_CONSTEXPR bool has_quiet_NaN = true;
static _GLIBCXX_USE_CONSTEXPR bool has_signaling_NaN = true;
static _GLIBCXX_USE_CONSTEXPR float_denorm_style has_denorm = denorm_present;
static _GLIBCXX_USE_CONSTEXPR bool has_denorm_loss = true;
static _GLIBCXX_USE_CONSTEXPR float_round_style round_style = round_toward_neg_infinity;
static _GLIBCXX_USE_CONSTEXPR bool is_iec559 = true;
static _GLIBCXX_USE_CONSTEXPR bool is_bounded = true;
static _GLIBCXX_USE_CONSTEXPR bool is_modulo = true;
static _GLIBCXX_USE_CONSTEXPR int digits = CHAR_BIT;
static _GLIBCXX_USE_CONSTEXPR int digits10 = CHAR_BIT;
static _GLIBCXX_USE_CONSTEXPR int max_digits10 = DECIMAL_DIG;
static _GLIBCXX_USE_CONSTEXPR int radix = FLT_RADIX;
static _GLIBCXX_USE_CONSTEXPR int min_exponent = FLT_MIN_EXP;
static _GLIBCXX_USE_CONSTEXPR int min_exponent10 = FLT_MIN_10_EXP;
static _GLIBCXX_USE_CONSTEXPR int max_exponent = FLT_MAX_EXP;
static _GLIBCXX_USE_CONSTEXPR int max_exponent10 = FLT_MAX_EXP;
static _GLIBCXX_USE_CONSTEXPR bool traps = true;
static _GLIBCXX_USE_CONSTEXPR bool tinyness_before = true;
static _GLIBCXX_CONSTEXPR int
min() _GLIBCXX_USE_NOEXCEPT { return CHAR_MIN ; }
static _GLIBCXX_CONSTEXPR int
lowest() _GLIBCXX_USE_NOEXCEPT { return CHAR_MIN ; }
static _GLIBCXX_CONSTEXPR int
max() _GLIBCXX_USE_NOEXCEPT { return CHAR_MAX ; }
static _GLIBCXX_CONSTEXPR int
epsilon() _GLIBCXX_USE_NOEXCEPT { return LDBL_EPSILON ; }
};
}
int main()
{
std::cout << std::boolalpha;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
//必须偏特化
// std::cout << "std::numeric_limits::epsilon(): "
// << std::numeric_limits::epsilon() << std::endl;
std::cout << "std::numeric_limits::epsilon(): "
<< std::numeric_limits::epsilon() << std::endl;
return 0;
} 输出
返回给定浮点类型的最大舍入误差
std::numeric_limits::round_error | static T round_error() throw(); |
(C++11 前) | |
| static constexpr T round_error() noexcept; |
(C++11 起) |
返回以 ULP （最后位置单位）表示的最大可能舍入错误，其为 ISO 10967 定义，可以从 0.5 （舍入到最近位）变化到 1.0 （舍入到零或无穷大）。它仅若 std::numeric_limits
返回值
T |
std::numeric_limits |
| /* non-specialized */ | T() |
| bool | false |
| char | 0 |
| signed char | 0 |
| unsigned char | 0 |
| wchar_t | 0 |
| char8_t | 0 |
| char16_t | 0 |
| char32_t | 0 |
| short | 0 |
| unsigned short | 0 |
| int | 0 |
| unsigned int | 0 |
| long | 0 |
| unsigned long | 0 |
| long long | 0 |
| unsigned long long | 0 |
| float | 0.5F |
| double | 0.5 |
| long double | 0.5L |
调用示例
#include
#include
#include
#include
#include
struct SName
{
};
//偏特化
struct SPartSpec
{
};
namespace std
{
template<>
struct numeric_limits
{
static _GLIBCXX_USE_CONSTEXPR bool is_specialized = true;
static _GLIBCXX_USE_CONSTEXPR bool is_signed = true;
static _GLIBCXX_USE_CONSTEXPR bool is_integer = true;
static _GLIBCXX_USE_CONSTEXPR bool is_exact = true;
static _GLIBCXX_USE_CONSTEXPR bool has_infinity = true;
static _GLIBCXX_USE_CONSTEXPR bool has_quiet_NaN = true;
static _GLIBCXX_USE_CONSTEXPR bool has_signaling_NaN = true;
static _GLIBCXX_USE_CONSTEXPR float_denorm_style has_denorm = denorm_present;
static _GLIBCXX_USE_CONSTEXPR bool has_denorm_loss = true;
static _GLIBCXX_USE_CONSTEXPR float_round_style round_style = round_toward_neg_infinity;
static _GLIBCXX_USE_CONSTEXPR bool is_iec559 = true;
static _GLIBCXX_USE_CONSTEXPR bool is_bounded = true;
static _GLIBCXX_USE_CONSTEXPR bool is_modulo = true;
static _GLIBCXX_USE_CONSTEXPR int digits = CHAR_BIT;
static _GLIBCXX_USE_CONSTEXPR int digits10 = CHAR_BIT;
static _GLIBCXX_USE_CONSTEXPR int max_digits10 = DECIMAL_DIG;
static _GLIBCXX_USE_CONSTEXPR int radix = FLT_RADIX;
static _GLIBCXX_USE_CONSTEXPR int min_exponent = FLT_MIN_EXP;
static _GLIBCXX_USE_CONSTEXPR int min_exponent10 = FLT_MIN_10_EXP;
static _GLIBCXX_USE_CONSTEXPR int max_exponent = FLT_MAX_EXP;
static _GLIBCXX_USE_CONSTEXPR int max_exponent10 = FLT_MAX_EXP;
static _GLIBCXX_USE_CONSTEXPR bool traps = true;
static _GLIBCXX_USE_CONSTEXPR bool tinyness_before = true;
static _GLIBCXX_CONSTEXPR int
min() _GLIBCXX_USE_NOEXCEPT { return CHAR_MIN ; }
static _GLIBCXX_CONSTEXPR int
lowest() _GLIBCXX_USE_NOEXCEPT { return CHAR_MIN ; }
static _GLIBCXX_CONSTEXPR int
max() _GLIBCXX_USE_NOEXCEPT { return CHAR_MAX ; }
static _GLIBCXX_CONSTEXPR int
epsilon() _GLIBCXX_USE_NOEXCEPT { return LDBL_EPSILON ; }
static _GLIBCXX_CONSTEXPR double
round_error() _GLIBCXX_USE_NOEXCEPT { return 0.5F ; }
};
}
int main()
{
std::cout << std::boolalpha;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
//必须偏特化
// std::cout << "std::numeric_limits::round_error(): "
// << std::numeric_limits::round_error() << std::endl;
std::cout << "std::numeric_limits::round_error(): "
<< std::numeric_limits::round_error() << std::endl;
return 0;
} 输出
返回给定类型的正无穷大值
std::numeric_limits::infinity | static T infinity() throw(); |
(C++11 前) | |
| static constexpr T infinity() noexcept; |
(C++11 起) |
返回浮点类型 T 所表示的特殊值“正无穷大”。仅若 std::numeric_limits
返回值
T |
std::numeric_limits |
| /* non-specialized */ | T() |
| bool | false |
| char | 0 |
| signed char | 0 |
| unsigned char | 0 |
| wchar_t | 0 |
| char8_t | 0 |
| char16_t | 0 |
| char32_t | 0 |
| short | 0 |
| unsigned short | 0 |
| int | 0 |
| unsigned int | 0 |
| long | 0 |
| unsigned long | 0 |
| long long | 0 |
| unsigned long long | 0 |
| float | HUGE_VALF |
| double | HUGE_VAL |
| long double | HUGE_VALL |
调用示例
#include
#include
#include
#include
#include
#include
struct SName
{
};
//偏特化
struct SPartSpec
{
};
namespace std
{
template<>
struct numeric_limits
{
static _GLIBCXX_USE_CONSTEXPR bool is_specialized = true;
static _GLIBCXX_USE_CONSTEXPR bool is_signed = true;
static _GLIBCXX_USE_CONSTEXPR bool is_integer = true;
static _GLIBCXX_USE_CONSTEXPR bool is_exact = true;
static _GLIBCXX_USE_CONSTEXPR bool has_infinity = true;
static _GLIBCXX_USE_CONSTEXPR bool has_quiet_NaN = true;
static _GLIBCXX_USE_CONSTEXPR bool has_signaling_NaN = true;
static _GLIBCXX_USE_CONSTEXPR float_denorm_style has_denorm = denorm_present;
static _GLIBCXX_USE_CONSTEXPR bool has_denorm_loss = true;
static _GLIBCXX_USE_CONSTEXPR float_round_style round_style = round_toward_neg_infinity;
static _GLIBCXX_USE_CONSTEXPR bool is_iec559 = true;
static _GLIBCXX_USE_CONSTEXPR bool is_bounded = true;
static _GLIBCXX_USE_CONSTEXPR bool is_modulo = true;
static _GLIBCXX_USE_CONSTEXPR int digits = CHAR_BIT;
static _GLIBCXX_USE_CONSTEXPR int digits10 = CHAR_BIT;
static _GLIBCXX_USE_CONSTEXPR int max_digits10 = DECIMAL_DIG;
static _GLIBCXX_USE_CONSTEXPR int radix = FLT_RADIX;
static _GLIBCXX_USE_CONSTEXPR int min_exponent = FLT_MIN_EXP;
static _GLIBCXX_USE_CONSTEXPR int min_exponent10 = FLT_MIN_10_EXP;
static _GLIBCXX_USE_CONSTEXPR int max_exponent = FLT_MAX_EXP;
static _GLIBCXX_USE_CONSTEXPR int max_exponent10 = FLT_MAX_EXP;
static _GLIBCXX_USE_CONSTEXPR bool traps = true;
static _GLIBCXX_USE_CONSTEXPR bool tinyness_before = true;
static _GLIBCXX_CONSTEXPR int
min() _GLIBCXX_USE_NOEXCEPT { return CHAR_MIN ; }
static _GLIBCXX_CONSTEXPR int
lowest() _GLIBCXX_USE_NOEXCEPT { return CHAR_MIN ; }
static _GLIBCXX_CONSTEXPR int
max() _GLIBCXX_USE_NOEXCEPT { return CHAR_MAX ; }
static _GLIBCXX_CONSTEXPR int
epsilon() _GLIBCXX_USE_NOEXCEPT { return LDBL_EPSILON ; }
static _GLIBCXX_CONSTEXPR double
round_error() _GLIBCXX_USE_NOEXCEPT { return 0.5F ; }
static _GLIBCXX_CONSTEXPR double
infinity() _GLIBCXX_USE_NOEXCEPT { return HUGE_VAL ; }
};
}
int main()
{
std::cout << std::boolalpha;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
//必须偏特化
// std::cout << "std::numeric_limits::infinity(): "
// << std::numeric_limits::infinity() << std::endl;
std::cout << "std::numeric_limits::infinity(): "
<< std::numeric_limits::infinity() << std::endl;
return 0;
} 输出
