Isnan
Defined in header <cmath>
.
Description
Determines if the given floating point number num
is a not-a-number (NaN
) value.
The library provides overloads for all cv-unqualified floating-point types as the type of the parameter num
(od C++23).
Additional Overloads are provided for all integer types, which are treated as double.
Declarations
- C++23
- C++11
// 1)
constexpr bool isnan( /* floating-point-type */ num );
// 2)
template< class Integer >
constexpr bool isnan( Integer num );
// 1)
bool isnan( float num );
// 2)
bool isnan( double num );
// 3)
bool isnan( long double num );
// 4)
template< class Integer >
bool isnan( Integer num );
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; }
.
The additional overloads are not required to be provided exactly as Additional Overloads.
They only need to be sufficient to ensure that for their argument num of integer type,
std::isnan(num)
has the same effect as std::isnan(static_cast<double>(num))
.
Examples
#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 - INFINITY) << '\n';
}
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