std::isnan
Defined in header <cmath> |
||
---|---|---|
bool isnan( float arg ); |
(1) | (since C++11) (constexpr since C++23) |
bool isnan( double arg ); |
(2) | (since C++11) (constexpr since C++23) |
bool isnan( long double arg ); |
(3) | (since C++11) (constexpr since C++23) |
bool isnan( IntegralType arg ); |
(4) | (since C++11) (constexpr since C++23) |
1-3) Determines if the given floating point number
arg
is a not-a-number (NaN) value.
4) A set of overloads or a function template accepting the
arg
argument of any
integral type. Equivalent to
(2) (the argument is cast to
double
).
Parameters
arg | - | floating point value |
Return value
true
if arg
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; }
Example
#include <iostream> #include <cmath> #include <cfloat> 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'; }
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
(C++11)(C++11)(C++11)
|
not-a-number (NaN) (function) |
(C++11)
|
categorizes the given floating-point value (function) |
(C++11)
|
checks if the given number has finite value (function) |
(C++11)
|
checks if the given number is infinite (function) |
(C++11)
|
checks if the given number is normal (function) |
(C++11)
|
checks if two floating-point values are unordered (function) |
C documentation for isnan |
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