INFINITY
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  
<cmath>
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|   #define INFINITY /*implementation defined*/ 
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(since C++11) | |
If the implementation supports floating-point infinities, the macro INFINITY expands to constant expression of type float which evaluates to positive or unsigned infinity.
If the implementation does not support floating-point infinities, the macro INFINITY expands to a positive value that is guaranteed to overflow a float at compile time, and the use of this macro generates a compiler warning.
[edit] See also
|    (C++11) 
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   checks if the given number is infinite   (function)  | 
|    (C++11)(C++11) 
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   indicates the overflow value for float, double and long double respectively    (macro constant)  | 
|    [static] 
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   identifies floating-point types that can represent the special value "positive infinity"   (public static member constant of std::numeric_limits) 
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|    [static] 
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   returns the positive infinity value of the given floating-point type  (public static member function of std::numeric_limits) 
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C documentation for INFINITY
 
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