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.
T
std::numeric_limits<T>::signaling_NaN() /* non-specialized */ T() bool false char â0â signed char â0â unsigned char â0â wchar_t â0â char8_t (since C++20) â0â char16_t (since C++11) â0â char32_t (since C++11) â0â short â0â unsigned short â0â int â0â unsigned int â0â long â0â unsigned long â0â long long (since C++11) â0â unsigned long long (since C++11) â0â float implementation-defined (may be FLT_SNAN) double implementation-defined (may be DBL_SNAN) long double implementation-defined (may be LDBL_SNAN) [edit] 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.
[edit] ExampleDemonstrates the use of a signaling NaN to raise a floating-point exception:
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[edit] See also identifies floating-point types that can represent the special value "signaling not-a-number" (NaN)
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