std::nan, std::nanf, std::nanl

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Defined in header <cmath>
float nanf( const char* arg );		(since C++11)
double nan( const char* arg );		(since C++11)
long double nanl( const char* arg );		(since C++11)

Converts the implementation-defined character string arg into the corresponding quiet NaN value. The call std::nan("string") is equivalent to the call std::strtod("NAN(string)", (char**)NULL);.

[edit] Parameters

arg

-

narrow character string identifying the contents of a NaN, or an empty string

[edit] Return value

The NaN value that corresponds to the identifying string arg or zero if the implemntation does not support quiet NaNs.

[edit] See also

isnan (C++11)	checks if the given number is NaN (function)
quiet_NaN [static]	returns the quiet NaN value of the given floating-point type (public static member function of std::numeric_limits)