std::log – cppreference.com

std::log

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definiert in Header <cmath>
float log( float arg );
double log( double arg );
long double log( long double arg );
double log( Integral arg );
 (seit C++11)

Computes the natural (base e) logarithm of arg.

Parameter

arg -
Floating-Point-Wert
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floating point value
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Rückgabewert

natural logarithm of arg.

Domain-Fehler tritt auf, wenn arg negativ ist. NAN wird in diesem Fall wieder .
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Domain error occurs if arg is negative. NAN is returned in that case.
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Bereichs-Fehler tritt auf, wenn arg ist 0. -HUGE_VAL wird in diesem Fall wieder .
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Range error occurs if arg is 0. -HUGE_VAL is returned in that case.
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Beispiel

The following code computes the binary (base 2) logarithm with help of natural logarithm. 

#include <cmath>
#include <iostream>
 
int main()
{
    double base = 2.0;
    double arg  = 256.0;
    double result = std::log(arg) / std::log(base);
 
    std::cout << result << '\n';
}

Output: 

8

Siehe auch