std::numeric_limits<T>::quiet_NaN
static T quiet_NaN() throw(); |
(until C++11) | |
static constexpr T quiet_NaN() noexcept; |
(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 |
char8_t (C++20) |
0 |
char16_t (C++11) |
0 |
char32_t (C++11) |
0 |
short |
0 |
unsigned short |
0 |
int |
0 |
unsigned int |
0 |
long |
0 |
unsigned long |
0 |
long long (C++11) |
0 |
unsigned long long (C++11) |
0 |
float |
implementation-defined (may be NAN ) |
double |
implementation-defined |
long double |
implementation-defined |
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).
#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 -nan NaN == 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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