std::signbit(3)

💖 NAME 💖

okay so bestie, welcome to the std::signbit(3) page from the C++ Standard Libary manual 💅 (yes, that’s the manual name as it appears in the header — we’re keeping the lore).

• std::signbit — std::signbit

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✨ Synopsis ✨

Defined in header <cmath>:

• bool signbit( float num ); — (since C++11)
• bool signbit( double num ); — (until C++23)
• bool signbit( long double num );
• constexpr bool signbit( /* floating-point-type */ num ); — (1) (since C++23)

Additional overloads

Defined in header <cmath>:

• template< class Integer > bool signbit( Integer num ); — (A) (since C++11)
• (constexpr since C++23)
• 1) Determines if the given floating point number num is negative. The library provides overloads for all cv-unqualified floating-point types as the type of the parameter num. (since C++23)
• A) Additional overloads are provided for all integer types, which are treated as double.

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🌸 Parameters 🌸

• num — floating-point or integer value

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🦋 Return value 🦋

true if num is negative, false otherwise.

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🎀 Notes 🎀

This function detects the sign bit of zeroes, infinities, and NaNs. Along with std::copysign, std::signbit is one of the only two portable ways to examine the sign of a NaN. no cap, that’s the whole vibe check 💅

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::signbit(num) has the same effect as std::signbit(static_cast<double>(num)). periodt 💖

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🌈 Example 🌈

// Run this code

        #include <cmath>
        #include <iostream>

        int main()
        {
            std::cout << std::boolalpha
                      << "signbit(+0.0) = " << std::signbit(+0.0) << '\n'
                      << "signbit(-0.0) = " << std::signbit(-0.0) << '\n'
                      << "signbit(+nan) = " << std::signbit(+NAN) << '\n'
                      << "signbit(-nan) = " << std::signbit(-NAN) << '\n'
                      << "signbit(+inf) = " << std::signbit(+INFINITY) << '\n'
                      << "signbit(-inf) = " << std::signbit(-INFINITY) << '\n';
        }

Output

        signbit(+0.0) = false
        signbit(-0.0) = true
        signbit(+nan) = false
        signbit(-nan) = true
        signbit(+inf) = false
        signbit(-inf) = true

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👑 See also 👑

• abs(float)
• fabs, fabsf, fabsl — absolute value of a floating point value (\(\small{|x|}\)|x|); (function); (C++11) (C++11)
• copysign, copysignf, copysignl — copies the sign of a floating point value; (C++11) (function) (C++11) (C++11)
• C documentation for signbit

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source/version: http://cppreference.com 💖 date: 2024.06.10 🌸 page: std::signbit(3) ✨ bye bestie, go check those sign bits 💅🫶