std::numeric_limits::quiet_NaN
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                    < cpp | types | numeric limits
                    
                                                            
                    | static T quiet_NaN(); | (until C++11) | |
| static constexpr T quiet_NaN(); | (since C++11) | |
Returns the special value "quiet not-a-number", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_quiet_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.
| Contents | 
[edit] Return value
| T | std::numeric_limits<T>::quiet_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 | NAN or another implementation-defined NaN | 
| double | implementation-defined | 
| long double | implementation-defined | 
[edit] Exceptions
| (none) | (until C++11) | 
| noexcept specification:   noexcept | (since C++11) | 
[edit] Notes
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
[edit] Example
Several ways to generate a NaN (the output string is compiler-specific)
Run this code
#include <iostream> #include <limits> #include <cmath> int main() { std::cout << std::numeric_limits<double>::quiet_NaN() << ' ' << std::numeric_limits<double>::signaling_NaN() << ' ' << std::acos(2) << ' ' << std::tgamma(-1) << ' ' << std::log(-1) << ' ' << std::sqrt(-1) << ' ' << 0 / 0.0 << '\n'; std::cout << "NaN == NaN? " << std::boolalpha << ( std::numeric_limits<double>::quiet_NaN() == std::numeric_limits<double>::quiet_NaN() ) << '\n'; }
Output:
nan nan nan nan nan -nan -nan NaN == NaN? false
[edit] See also
| [static] | identifies floating-point types that can represent the special value "quiet not-a-number" (NaN) (public static member constant) | 
| [static] | returns a signaling NaN value of the given floating-point type (public static member function) | 


