NAME

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

Synopsis

Defined in header <cmath>
float nanf( const char* arg ); (1) (since C++11)
double nan( const char* arg ); (2) (since C++11)
long double nanl( const char* arg ); (3) (since C++11)

Converts the character string arg into the corresponding quiet NaN value, as if by
calling std::strtof, std::strtod, or std::strtold, respectively.

1) The call std::nanf("n-char-sequence"), where n-char-sequence is a sequence of
digits, ASCII letters, and underscores, is equivalent to the call
std::strtof("NAN(n-char-sequence)", (char**)nullptr);.
The call std::nanf("") is equivalent to the call std::strtof("NAN()",
(char**)nullptr);.
The call std::nanf("string"), where string is neither an n-char-sequence nor an
empty string, is equivalent to the call std::strtof("NAN", (char**)nullptr);.
2) Same as (1), but calls std::strtod instead of std::strtof.
3) Same as (1), but calls std::strtold instead of std::strtof.

Parameters

arg - narrow character string identifying the contents of a NaN

Return value

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

If the implementation supports IEEE floating-point arithmetic (IEC 60559), it also
supports quiet NaNs.

Error handling

This function is not subject to any of the error conditions specified in
math_errhandling.

Example

// Run this code

#include <iostream>
#include <cmath>
#include <cstdint>
#include <cstring>

int main()
{
double f1 = std::nan("1");
std::uint64_t f1n; std::memcpy(&f1n, &f1, sizeof f1);
std::cout << "nan(\"1\") = " << f1 << " (" << std::hex << f1n << ")\n";

double f2 = std::nan("2");
std::uint64_t f2n; std::memcpy(&f2n, &f2, sizeof f2);
std::cout << "nan(\"2\") = " << f2 << " (" << std::hex << f2n << ")\n";
}

Possible output:

nan("1") = nan (7ff0000000000001)
nan("2") = nan (7ff0000000000002)

See also

isnan checks if the given number is NaN
(C++11) (function)
NAN evaluates to a quiet NaN of type float
(C++11) (macro constant)
has_quiet_NaN identifies floating-point types that can represent the special
[static] value "quiet not-a-number" (NaN)
(public static member constant of std::numeric_limits<T>)
has_signaling_NaN identifies floating-point types that can represent the special
[static] value "signaling not-a-number" (NaN)
(public static member constant of std::numeric_limits<T>)
quiet_NaN returns a quiet NaN value of the given floating-point type
[static] (public static member function of std::numeric_limits<T>)
signaling_NaN returns a signaling NaN value of the given floating-point type
[static] (public static member function of std::numeric_limits<T>)