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std::numeri...gnaling_NaN(3) C++ Standard Libary std::numeri...gnaling_NaN(3) NAME std::numeric_limits::signaling_NaN - std::numeric_limits::signaling_NaN Synopsis 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_lim- its<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>::signal- ing_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 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 im- plementation do. When a signaling NaN is used as an argument to an arithmetic expres- sion, 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: // Run this code #include <cfenv> #include <iostream> #include <limits> #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 has_signaling_NaN identifies floating-point types that can represent the special [static] value "signaling not-a-number" (NaN) (public static member constant) quiet_NaN returns a quiet NaN value of the given floating- point type [static] (public static member function) isnan checks if the given number is NaN (C++11) (function) http://cppreference.com 2024.06.10 std::numeri...gnaling_NaN(3)
NAME | Synopsis | Return value | Notes | Example | Output: | See also
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