std::nan,std::nanf,std::nanl (3) - Linux Manuals

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

NAME

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

Synopsis

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, 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

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.

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)