std::log

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Defined in header <cmath>
float       log( float arg );
double      log( double arg );
long double log( long double arg );
double      log( Integral arg );		(since C++11)

Computes the natural (base e) logarithm of arg.

Parameters

arg

-

floating point value

Return value

natural logarithm of arg.

Domain error occurs if arg is negative. NAN is returned in that case.

Range error occurs if arg is ​0​. -HUGE_VAL is returned in that case.

Example

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

See also

exp	returns e raised to the given power (ex) (function)
log10	computes common (base 10) logarithm (log10(x)) (function)
pow	raises a number to the given power (xy) (function)
log(std::complex)	complex natural logarithm with the branch cuts along the negative real axis (function template)
log(std::valarray)	applies the function std::log to each element of valarray (function template)