std::isnan
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <cmath> | ||
| bool isnan( float arg ); | (since C++11) | |
| bool isnan( double arg ); | (since C++11) | |
| bool isnan( long double arg ); | (since C++11) | |
Determines if the given floating point number arg is not-a-number (NaN).
| Contents | 
[edit] Parameters
| arg | - | floating point value | 
[edit] Return value
true if arg is NaN, false otherwise
[edit] Notes
In C, isnan is a preprocessor macro, rather than a function.
[edit] See also
| (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 | |


