std::nan,st...f,std::nanl(3)

💖 NAME 💖

okay so this is the C++ Standard Library manual page — header literally says C++ Standard Libary, no cap — for std::nan, std::nanf, and std::nanl, a.k.a. std::nan,st...f,std::nanl(3) 💖

std::nan, std::nanf, std::nanl — yes bestie, the name line is that trio, and the description line is the exact same trio again: std::nan,std::nanf,std::nanl. Iconic repetition, honestly 💅

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✨ 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)

so what’s the tea? These convert the character string arg into the corresponding quiet NaN value, as if by calling std::strtof, std::strtod, or std::strtold, respectively. Lowkey magical ✨

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.

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🌸 Parameters 🌸

• arg — narrow character string identifying the contents of a NaN. That’s it, bestie 🫶

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🎀 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. Slay 💅

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🦋 Error handling 🦋

This function is not subject to any of the error conditions specified in math_errhandling. So no extra error-handling drama here, bestie. Periodt 💀

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🍓 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)

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🌈 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 value "quiet not-a-number" (NaN) [static] (public static member constant of std::numeric_limits<T>)
• has_signaling_NaN — identifies floating-point types that can represent the special value "signaling not-a-number" (NaN) [static] (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>)
• C documentation for nanf, nan, nanl

okay that’s the whole page, bestie 🫶 source/version/date tea: http://cppreference.com, 2024.06.10, std::nan,st...f,std::nanl(3). Mwah 💋