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

float       nanf( const char* arg );

double      nan( const char* arg );

long double nanl( const char* arg );

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

The call std::nan("n-char-sequence"), where n-char-sequence is a sequence of digits, Latin letters, and underscores, is equivalent to the call std::strtod("NAN(n-char-sequence)", (char**)nullptr);.

The call std::nan("") is equivalent to the call std::strtod("NAN()", (char**)nullptr);.

The call std::nan("string"), where string is neither an n-char-sequence nor an empty string, is equivalent to the call std::strtod("NAN", (char**)nullptr);.

Parameters

Return value

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

Example

#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";
}

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

See also