Defined in header <cmath> | ||
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bool isnan( float arg ); | (1) | (since C++11) |
bool isnan( double arg ); | (2) | (since C++11) |
bool isnan( long double arg ); | (3) | (since C++11) |
bool isnan( IntegralType arg ); | (4) | (since C++11) |
arg is a not-a-number (NaN) value.arg argument of any integral type. Equivalent to (2) (the argument is cast to double). | arg | - | floating point value |
true if arg is a NaN, false otherwise.
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; }
#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
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(C++11)(C++11)(C++11) | not-a-number (NaN) (function) |
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(C++11) | categorizes the given floating point value (function) |
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(C++11) | checks if the given number has finite value (function) |
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(C++11) | checks if the given number is infinite (function) |
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(C++11) | checks if the given number is normal (function) |
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(C++11) | checks if two floating-point values are unordered (function) |
C documentation for isnan |
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