std::log

 

C++

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Common mathematical functions

Functions
Basic operations
abs(int) labs llabs imaxabs (C++11) abs(float) fabs div ldiv lldiv imaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nan nanf nanl (C++11) (C++11) (C++11)
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erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
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ceil floor round lround llround (C++11) (C++11) (C++11)	trunc (C++11) nearbyint (C++11) rint lrint llrint (C++11) (C++11) (C++11)
Floating point manipulation functions
ldexp scalbn scalbln (C++11) (C++11) ilogb (C++11) logb (C++11)	frexp modf nextafter nexttoward (C++11) (C++11) copysign (C++11)
Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Macro constants
HUGE_VALF HUGE_VAL HUGE_VALL (C++11) (C++11) INFINITY (C++11) NAN (C++11) math_errhandling MATH_ERRNO MATH_ERREXCEPT (C++11)	FP_NORMAL FP_SUBNORMAL FP_ZERO FP_INFINITE FP_NAN (C++11) (C++11) (C++11) (C++11) (C++11)

 

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.

run this code

#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)