NAME

std::numeric_limits::quiet_NaN - std::numeric_limits::quiet_NaN

Synopsis

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)

// Run this code

#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: