std::numeric_limits::quiet_NaN
static T quiet_NaN(); | ? | (until C++11) |
|---|---|---|
static constexpr T quiet_NaN(); | ? | (since C++11) |
返回特殊值“静默”。无号“，由浮点类型表示。T.只有在以下情况下才有意义std::numeric_limits<T>::has_quiet_NaN==true在ieee 754中，浮点数最常见的二进制表示形式，指数集的所有位数和分数集的至少一位的任何值都代表NaN。它是实现-定义的分数的值代表安静或信令的nans，以及符号位是否有意义。
返回值
T | std::numeric_limits<T>::quiet_NaN() |
|---|---|
/* non-specialized */ | T(); |
bool | false |
char | ?0? |
signed char | ?0? |
unsigned char | ?0? |
wchar_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 | NAN or another implementation-defined NaN |
double | implementation-defined |
long double | implementation-defined |
例外
(none) | (until C++11) |
|---|---|
noexcept specification: noexcept | (since C++11) |
注记
NaN从来都比不上它自己。复制NAN可能不会保留其位表示形式。
例
生成NaN%28输出字符串的几种方法是编译器特有的%29。
二次
#include <iostream>
#include <limits>
#include <cmath>
int main()
{
std::cout << std::numeric_limits<double>::quiet_NaN() << ' '
<< std::numeric_limits<double>::signaling_NaN() << ' '
<< std::acos(2) << ' '
<< std::tgamma(-1) << ' '
<< std::log(-1) << ' '
<< std::sqrt(-1) << ' '
<< 0 / 0.0 << '\n';
std::cout << "NaN == NaN? " << std::boolalpha
<< ( std::numeric_limits<double>::quiet_NaN()
== std::numeric_limits<double>::quiet_NaN() ) << '\n';
}二次
产出：
二次
nan nan nan nan nan -nan -nan
NaN == NaN? false二次
另见
has_quiet_NaN static | identifies floating-point types that can represent the special value "quiet not-a-number" (NaN) (public static member constant) |
|---|---|
signaling_NaN static | returns a signaling NaN value of the given floating-point type (public static member function) |
nannanfnanl (C++11)(C++11)(C++11) | not-a-number (NaN) (function) |
isnan (C++11) | checks if the given number is NaN (function) |
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