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Difference between revisions of "cpp/numeric/math/signbit"

From cppreference.com
< cpp‎ | numeric‎ | math
 
m (→‎Example: +nan)
 
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{{cpp/title|signbit}}
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{{cpp/numeric/math/unary_is|signbit
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{{cpp/numeric/math/sidebar}}
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|description= Determines if the given floating point number {{c|num}} is negative.
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{{ddcl list begin}}
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|condition=is negative
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{{ddcl list header | cmath}}
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|note=
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{{ddcl list item | notes={{mark c++0x feature}} |
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This function detects the sign bit of zeroes, infinities, and NaNs. Along with {{lc|std::copysign}}, {{tt|std::signbit}} is one of the only two portable ways to examine the sign of a NaN.
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int signbit( float arg );
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}}
 
}}
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{{ddcl list item | notes={{mark c++0x feature}} |
 
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int signbit( double arg );
 
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}}
 
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{{ddcl list item | notes={{mark c++0x feature}} |
 
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int signbit( long double arg );
 
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}}
 
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{{ddcl list end}}
 
  
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===Example===
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{{example
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|code=
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#include <cmath>
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#include <iostream>
  
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Determines if the given floating point number {{tt|arg}} is negative.
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int main()
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{
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<!-- ======== -->
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    std::cout << std::boolalpha
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{{params}}
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              << "signbit(+0.0) = " << std::signbit(+0.0) << '\n'
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{{param list begin}}
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              << "signbit(-0.0) = " << std::signbit(-0.0) << '\n'
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{{param list item | arg | floating point value}}
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              << "signbit(+nan) = " << std::signbit(+NAN) << '\n'
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{{param list end}}
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              << "signbit(-nan) = " << std::signbit(-NAN) << '\n'
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              << "signbit(+inf) = " << std::signbit(+INFINITY) << '\n'
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<!-- ======== -->
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              << "signbit(-inf) = " << std::signbit(-INFINITY) << '\n';
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{{returns}}
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}
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|output=
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nonzero value if {{tt|arg}} is negative, {{cpp|0}} otherwise
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signbit(+0.0) = false
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signbit(-0.0) = true
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signbit(+nan) = false
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signbit(-nan) = true
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signbit(+inf) = false
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signbit(-inf) = true
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}}
  
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<!-- ======== -->
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===See also===
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{{see also}}
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{{dsc begin}}
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{{dsc inc|cpp/numeric/math/dsc fabs}}
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{{dsc inc|cpp/numeric/math/dsc copysign}}
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{{dsc see c|c/numeric/math/signbit}}
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{{dsc end}}
  
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{{dcl list begin}}
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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{{dcl list template | cpp/numeric/math/dcl list fabs}}
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{{dcl list template | cpp/numeric/math/dcl list copysign}}
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{{dcl list end}}
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Latest revision as of 14:46, 21 March 2023

 
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Defined in header <cmath>
(1)
bool signbit( float num );

bool signbit( double num );

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

Contents

[edit] Parameters

num - floating-point or integer value

[edit] Return value

true if num is negative, false otherwise.

[edit] 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.

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)).

[edit] 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

[edit] See also

(C++11)(C++11)
 absolute value of a floating point value (|x|)
(function) [edit]
(C++11)(C++11)(C++11)
 copies the sign of a floating point value
(function) [edit]
C documentation for signbit
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