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| Basic types | |||||||||||||||||||||
| Fixed width integer types(C++11) | |||||||||||||||||||||
| Fixed width floating-point types(C++23) | |||||||||||||||||||||
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| Numeric limits | |||||||||||||||||||||
| C numeric limits interface | |||||||||||||||||||||
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| Static constants | ||||
(C++11) | ||||
| Static member functions | ||||
(C++11) | ||||
numeric_limits::quiet_NaN | ||||
| Helper types | ||||
static T quiet_NaN()throw(); | (until C++11) | |
staticconstexpr T quiet_NaN()noexcept; | (since C++11) | |
Returns the special value "quietnot-a-number", as represented by the floating-point typeT. Only meaningful ifstd::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 |
T | std::numeric_limits<T>::quiet_NaN() |
| /* non-specialized */ | T() |
| bool | false |
| char | 0 |
| signedchar | 0 |
| unsignedchar | 0 |
| wchar_t | 0 |
| char8_t(since C++20) | 0 |
| char16_t(since C++11) | 0 |
| char32_t(since C++11) | 0 |
| short | 0 |
| unsignedshort | 0 |
| int | 0 |
| unsignedint | 0 |
| long | 0 |
| unsignedlong | 0 |
| longlong(since C++11) | 0 |
| unsignedlonglong(since C++11) | 0 |
| float | implementation-defined (may beNAN) |
| double | implementation-defined |
| longdouble | implementation-defined |
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
Several ways to generate a NaN (the output string is compiler-specific):
#include <iostream>#include <limits>#include <cmath> int main(){std::cout<<std::numeric_limits<double>::quiet_NaN()<<' '// nan<<std::numeric_limits<double>::signaling_NaN()<<' '// nan<<std::acos(2)<<' '// nan<<std::tgamma(-1)<<' '// nan<<std::log(-1)<<' '// nan<<std::sqrt(-1)<<' '// -nan<<0/0.0<<'\n';// -nan std::cout<<"NaN == NaN? "<<std::boolalpha<<(std::numeric_limits<double>::quiet_NaN()==std::numeric_limits<double>::quiet_NaN())<<'\n';}
Possible output:
nan nan nan nan nan -nan -nanNaN == NaN? false
[static] | identifies floating-point types that can represent the special value "quiet not-a-number" (NaN) (public static member constant)[edit] |
[static] | returns a signaling NaN value of the given floating-point type (public static member function)[edit] |
(C++11)(C++11)(C++11) | not-a-number (NaN) (function)[edit] |
(C++11) | checks if the given number is NaN (function)[edit] |
