std::numeric_limits<T>::signaling_NaN - cppreference.com
From cppreference.com
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(until C++11) | |
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(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
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std::numeric_limits<T>::signaling_NaN()
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/* non-specialized */
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T()
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bool
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false
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char
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0
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signed char
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0
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unsigned char
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0
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wchar_t
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0
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char8_t (since C++20)
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0
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char16_t (since C++11)
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0
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char32_t (since C++11)
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0
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short
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0
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unsigned short
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0
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int
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0
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unsigned int
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0
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long
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0
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unsigned long
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0
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long long (since C++11)
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0
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unsigned long long (since C++11)
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0
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float
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implementation-defined (may be FLT_SNAN) |
double
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implementation-defined (may be DBL_SNAN) |
long double
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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 <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
| identifies floating-point types that can represent the special value "signaling not-a-number" (NaN) (public static member constant) [edit] | |
| returns a quiet NaN value of the given floating-point type (public static member function) [edit] | |
| checks if the given number is NaN (function) [edit] |