| (until C++11) | |||
| (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.
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 |
Exceptions
| (none) | (until C++11) |
noexcept specification: noexcept | (since C++11) |
Notes
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
Example
Several ways to generate a NaN (the output string is compiler-specific).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | #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:
1 2 | nan nan nan nan nan -nan -nanNaN == NaN? false |
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) |
| (C++11)(C++11)(C++11) | not-a-number (NaN) (function) |
| (C++11) | checks if the given number is NaN (function) |
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