std::log,std::logf,std::logl(3)

NAME
std::log,std::logf,std::logl - std::log,std::logf,std::logl

Synopsis
   Defined in header <cmath>
   float log ( float arg );
   float logf( float arg ); (since C++11)
   double log ( double arg ); (1) (2)
   long double log ( long double arg );
   long double logl( long double arg ); (3) (since C++11)
   double log ( IntegralType arg ); (4) (since C++11)
   1-3) Computes the natural (base e) logarithm of arg.
   4) A set of overloads or a function template accepting an argument of any integral
   type. Equivalent to (2) (the argument is cast to double).

Parameters
   arg - value of floating-point or Integral type

Return value
   If no errors occur, the natural (base-e) logarithm of arg (ln(arg) or log
   e(arg)) is returned.
   If a domain error occurs, an implementation-defined value is returned (NaN where
   supported)
   If a pole error occurs, -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL is returned.

Error handling
   Errors are reported as specified in math_errhandling.
   Domain error occurs if arg is less than zero.
   Pole error may occur if arg is zero.
   If the implementation supports IEEE floating-point arithmetic (IEC 60559),
     * If the argument is ±0, -∞ is returned and FE_DIVBYZERO is raised.
     * If the argument is 1, +0 is returned
     * If the argument is negative, NaN is returned and FE_INVALID is raised.
     * If the argument is +∞, +∞ is returned
     * If the argument is NaN, NaN is returned

Example
// Run this code
 #include <iostream>
 #include <cmath>
 #include <cerrno>
 #include <cstring>
 #include <cfenv>
 // #pragma STDC FENV_ACCESS ON
 int main()
 {
     std::cout << "log(1) = " << std::log(1) << '\n'
               << "base-5 logarithm of 125 = " << std::log(125)/std::log(5) << '\n';
     // special values
     std::cout << "log(1) = " << std::log(1) << '\n'
               << "log(+Inf) = " << std::log(INFINITY) << '\n';
     // error handling
     errno = 0;
     std::feclearexcept(FE_ALL_EXCEPT);
     std::cout << "log(0) = " << std::log(0) << '\n';
     if (errno == ERANGE)
         std::cout << " errno == ERANGE: " << std::strerror(errno) << '\n';
     if (std::fetestexcept(FE_DIVBYZERO))
         std::cout << " FE_DIVBYZERO raised\n";
 }

Possible output:
 log(1) = 0
 base-5 logarithm of 125 = 3
 log(1) = 0
 log(+Inf) = inf
 log(0) = -inf
     errno == ERANGE: Numerical result out of range
     FE_DIVBYZERO raised

See also
   log10
   log10f computes common (base 10) logarithm (\({\small \log_{10}{x}
   log10l }\)log[10](x))
   (C++11) (function)
   (C++11)
   log2
   log2f base 2 logarithm of the given number (\({\small \log_{2}{x}
   log2l }\)log[2](x))
   (C++11) (function)
   (C++11)
   (C++11)
   log1p
   log1pf natural logarithm (to base e) of 1 plus the given number
   log1pl (\({\small \ln{(1+x)} }\)ln(1+x))
   (C++11) (function)
   (C++11)
   (C++11)
   exp
   expf returns e raised to the given power (\({\small e^x}\)e^x)
   expl (function)
   (C++11)
   (C++11)
                      complex natural logarithm with the branch cuts along the negative
   log(std::complex) real axis
                      (function template)
   log(std::valarray) applies the function std::log to each element of valarray
                      (function template)