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std::isnan(3)		      C++ Standard Libary		 std::isnan(3)

NAME
       std::isnan - std::isnan

Synopsis
	  Defined in header <cmath>
	  bool isnan( float num	);
								       (since
       C++11)
	  bool	isnan( double num );					(until
       C++23)

	  bool isnan( long double num );
	  constexpr bool isnan(	/* floating-point-type */ num  (1)	(since
       C++23)
	  );
	  Additional overloads
	  Defined in header <cmath>
	  template<  class Integer >				    (A)	(since
       C++11)
	  bool isnan( Integer num );				       (const-
       expr since C++23)

	  1) Determines	if the given floating point number num is a not-a-num-
       ber (NaN) value.
	  The library provides overloads for all cv-unqualified	floating-point
       types as	the
	  type of the parameter	num.
	  (since C++23)
	  A) Additional	overloads are provided for all	integer	 types,	 which
       are treated as
	  double.

Parameters
	  num -	floating-point or integer value

Return value
	  true if num is a NaN,	false otherwise.

Notes
	  There	 are  many  different  NaN values with different sign bits and
       payloads, see
	  std::nan and std::numeric_limits::quiet_NaN.

	  NaN values never compare equal to themselves or to other NaN values.
       Copying a NaN
	  is not required, by IEEE-754,	to  preserve  its  bit	representation
       (sign and payload),
	  though most implementation do.

	  Another  way	to test	if a floating-point value is NaN is to compare
       it with itself:
	  bool is_nan(double x)	{ return x != x; }.

	  GCC and Clang	support	a -ffinite-math	option	(additionally  implied
       by -ffast-math),
	  which	 allows	 the respective	compiler to assume the nonexistence of
       special IEEE-754
	  floating point values	such as	NaN, infinity, or  negative  zero.  In
       other words,
	  std::isnan is	assumed	to always return false under this option.

	  The  additional overloads are	not required to	be provided exactly as
       (A). They only
	  need to be sufficient	to ensure that for their argument num of inte-
       ger type,
	  std::isnan(num) has the same effect  as  std::isnan(static_cast<dou-
       ble>(num)).

Example
       // Run this code

	#include <cfloat>
	#include <cmath>
	#include <iostream>

	int main()
	{
	    std::cout << std::boolalpha
		      << "isnan(NaN) = " << std::isnan(NAN) << '\n'
		      << "isnan(Inf) = " << std::isnan(INFINITY) << '\n'
		      << "isnan(0.0) = " << std::isnan(0.0) << '\n'
		      <<  "isnan(DBL_MIN/2.0) =	" << std::isnan(DBL_MIN	/ 2.0)
       << '\n'
		      << "isnan(0.0 / 0.0)   = " << std::isnan(0.0 /  0.0)  <<
       '\n'
		      <<  "isnan(Inf - Inf)   =	" << std::isnan(INFINITY - IN-
       FINITY) << '\n';
	}

Output:
	isnan(NaN) = true
	isnan(Inf) = false
	isnan(0.0) = false
	isnan(DBL_MIN/2.0) = false
	isnan(0.0 / 0.0)   = true
	isnan(Inf - Inf)   = true

See also
	  nan
	  nanf
	  nanl	      not-a-number (NaN)
	  (C++11)     (function)
	  (C++11)
	  (C++11)
	  fpclassify  categorizes the given floating-point value
	  (C++11)     (function)
	  isfinite    checks if	the given number has finite value
	  (C++11)     (function)
	  isinf	      checks if	the given number is infinite
	  (C++11)     (function)
	  isnormal    checks if	the given number is normal
	  (C++11)     (function)
	  isunordered checks if	two floating-point values are unordered
	  (C++11)     (function)
	  C documentation for
	  isnan

http://cppreference.com		  2024.06.10			 std::isnan(3)

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