static T signaling_NaN(); | (until C++11) | |
static constexpr T signaling_NaN(); | (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 |
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 | implementation-defined |
double | implementation-defined |
long double | implementation-defined |
Exceptions
(none) | (until C++11) |
noexcept specification: noexcept | (since C++11) |
Notes
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
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) |
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