std::numeric_limits<T>::signaling_NaN
| static T signaling_NaN() throw(); |
(until C++11) | |
| static constexpr T signaling_NaN() noexcept; |
(since C++11) | |
Returns the special value "signaling not-a-number", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_signaling_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.
Return value
T
|
std::numeric_limits<T>::signaling_NaN() |
| /* non-specialized */ | T()
|
| bool | false |
| char | 0 |
| signed char | 0 |
| unsigned char | 0 |
| wchar_t | 0 |
| char8_t (C++20) | 0 |
| char16_t (C++11) | 0 |
| char32_t (C++11) | 0 |
| short | 0 |
| unsigned short | 0 |
| int | 0 |
| unsigned int | 0 |
| long | 0 |
| unsigned long | 0 |
| long long (C++11) | 0 |
| unsigned long long (C++11) | 0 |
| float | implementation-defined (may be FLT_SNAN) |
| double | implementation-defined (may be DBL_SNAN) |
| long double | implementation-defined (may be LDBL_SNAN) |
Notes
A NaN never compares equal to itself. Copying a NaN is not required, by IEEE-754, to preserve its bit representation (sign and payload), though most implementation do.
When a signaling NaN is used as an argument to an arithmetic expression, the appropriate floating-point exception may be raised and the NaN is "quieted", that is, the expression returns a quiet NaN.
Example
Demonstrates the use of a signaling NaN to raise a floating-point exception
#include <iostream> #include <limits> #include <cfenv> #pragma STDC_FENV_ACCESS on void show_fe_exceptions() { int n = std::fetestexcept(FE_ALL_EXCEPT); if(n & FE_INVALID) std::cout << "FE_INVALID is raised\n"; else if(n == 0) std::cout << "no exceptions are raised\n"; std::feclearexcept(FE_ALL_EXCEPT); } int main() { double snan = std::numeric_limits<double>::signaling_NaN(); std::cout << "After sNaN was obtained "; show_fe_exceptions(); double qnan = snan * 2.0; std::cout << "After sNaN was multiplied by 2 "; show_fe_exceptions(); double qnan2 = qnan * 2.0; std::cout << "After the quieted NaN was multiplied by 2 "; show_fe_exceptions(); std::cout << "The result is " << qnan2 << '\n'; }
Output:
After sNaN was obtained no exceptions are raised After sNaN was multiplied by 2 FE_INVALID is raised After the quieted NaN was multiplied by 2 no exceptions are raised The result is nan
See also
| [static] |
identifies floating-point types that can represent the special value "signaling not-a-number" (NaN) (public static member constant) |
| [static] |
returns a quiet NaN value of the given floating-point type (public static member function) |
| (C++11) |
checks if the given number is NaN (function) |