static T quiet_NaN() throw(); | (until C++11) | |
static constexpr T quiet_NaN() noexcept; | (since C++11) |
Returns the special value "quiet not-a-number", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_quiet_NaN == true. In IEEE 754, the most common binary representation of floating-point numbers, any value with all bits of the exponent set and at least one bit of the fraction set represents a NaN. It is implementation-defined which values of the fraction represent quiet or signaling NaNs, and whether the sign bit is meaningful.
T | std::numeric_limits<T>::quiet_NaN() |
|---|---|
| /* non-specialized */ | T() |
| bool | false |
| char | 0 |
| signed char | 0 |
| unsigned char | 0 |
| wchar_t | 0 |
| char8_t (since C++20) | 0 |
| char16_t (since C++11) | 0 |
| char32_t (since C++11) | 0 |
| short | 0 |
| unsigned short | 0 |
| int | 0 |
| unsigned int | 0 |
| long | 0 |
| unsigned long | 0 |
| long long (since C++11) | 0 |
| unsigned long long (since C++11) | 0 |
| float | implementation-defined (may be NAN) |
| double | implementation-defined |
| long double | implementation-defined |
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
Several ways to generate a NaN (the output string is compiler-specific):
#include <iostream>
#include <limits>
#include <cmath>
int main()
{
std::cout << std::numeric_limits<double>::quiet_NaN() << ' ' // nan
<< std::numeric_limits<double>::signaling_NaN() << ' ' // nan
<< std::acos(2) << ' ' // nan
<< std::tgamma(-1) << ' ' // nan
<< std::log(-1) << ' ' // nan
<< std::sqrt(-1) << ' ' // -nan
<< 0 / 0.0 << '\n'; // -nan
std::cout << "NaN == NaN? " << std::boolalpha
<< ( std::numeric_limits<double>::quiet_NaN() ==
std::numeric_limits<double>::quiet_NaN() ) << '\n';
}Possible output:
nan nan nan nan nan -nan -nan NaN == NaN? false
|
[static] | identifies floating-point types that can represent the special value "quiet not-a-number" (NaN) (public static member constant) |
|
[static] | returns a signaling NaN value of the given floating-point type (public static member function) |
|
(C++11)(C++11)(C++11) | not-a-number (NaN) (function) |
|
(C++11) | checks if the given number is NaN (function) |
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