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

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< cpp‎ | numeric‎ | math

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

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

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