Defined in header
<cmath> | ||
---|---|---|
float log( float arg ); | (1) | |
double log( double arg ); | (2) | |
long double log( long double arg ); | (3) | |
double log( Integral arg ); | (4) | (since C++11) |
arg
.double
).arg | - | value of floating-point or Integral type |
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.
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),
FE_DIVBYZERO
is raised. FE_INVALID
is raised. #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
computes common (base 10) logarithm (log10(x)) (function) |
|
(C++11)
| base 2 logarithm of the given number (log2(x)) (function) |
(C++11)
| natural logarithm (to base e) of 1 plus the given number (ln(1+x)) (function) |
returns e raised to the given power (ex) (function) |
|
complex natural logarithm with the branch cuts along the negative real axis (function template) |
|
applies the function std::log to each element of valarray (function template) |
|
C documentation for log |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/numeric/math/log