Std::log,std::logf,std::logl (3) Linux Manual Page

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

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

std::log,std::logf,std::logl (3) Linux Manual Page