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 num );
   double log ( double num ); (until C++23)
   long double log ( long double num );
   /* floating-point-type */ (since C++23)
               log ( /* floating-point-type */ num ); (constexpr since C++26)
   float logf( float num ); (1) (2) (since C++11)
                        (constexpr since C++26)
   long double logl( long double num ); (3) (since C++11)
                        (constexpr since C++26)
   Additional overloads (since C++11)
   Defined in header <cmath>
   template< class Integer > (A) (constexpr since C++26)
   double log ( Integer num );
   1-3) Computes the natural (base e) logarithm of num.
   The library provides overloads of std::log for all cv-unqualified floating-point
   types as the type of the parameter.
   (since C++23)
   A) Additional overloads are provided for all integer types, which are (since C++11)
   treated as double.

Parameters
   num - floating-point or integer value

Return value
   If no errors occur, the natural (base-e) logarithm of num (ln(num) or log
   e(num)) 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 num is less than zero.
   Pole error may occur if num 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.

Notes
   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::log(num) has the same effect as std::log(static_cast<double>(num)).

Example
// Run this code
 #include <cerrno>
 #include <cfenv>
 #include <cmath>
 #include <cstring>
 #include <iostream>
 // #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
   log10l (\({\small\log_{10}{x}}\)log[10](x))
   (C++11) (function)
   (C++11)
   log2
   log2f base 2 logarithm of the given number
   log2l (\({\small\log_{2}{x}}\)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)
   C documentation for
   log