From cppreference.com
Defined in header
floatlog(floatnum);doublelog(doublenum);longdoublelog(longdoublenum); (1)(until C++23)/*floating-point-type*/log(/*floating-point-type*/num);(since C++23)
(constexpr since C++26)floatlogf(floatnum); (2)(since C++11)
(constexpr since C++26)longdoublelogl(longdoublenum); (3)(since C++11)
(constexpr since C++26)
(since C++26)
Defined in header
template</*math-floating-point*/V>constexpr/*deduced-simd-t*/<V>log(constV&v_num); (S) (since C++26)
(since C++11)
Defined in header
template<classInteger>doublelog(Integernum); (A)(constexpr since C++26)1-3) Computes the
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 treated as double.
(since C++11)Parameters
num - floating-point or integer value Return value
If no errors occur, the natural (base-e) logarithm of num (ln(num) or loge(num)) is returned.
If a domain error occurs, an implementation-defined value is returned (NaN where supported).
If a pole error occurs,
, -HUGE_VALF, or -HUGE_VALL is returned.
Error handling
Errors are reported as specified in
.
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
is raised.
If the argument is 1, +0 is returned.
If the argument is negative, NaN is returned and
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 ONintmain(){std::cout<<"log(1) = "<<std::log(1)<<'\n'<<"base-5 logarithm of 125 = "<<std::log(125)/std::log(5)<<'\n';// special valuesstd::cout<<"log(1) = "<<std::log(1)<<'\n'<<"log(+Inf) = "<<std::log(INFINITY)<<'\n';// error handlingerrno=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
(C++11)(C++11)
computes common (base 10) logarithm (log10(x))
(function)
(C++11)(C++11)(C++11)
base 2 logarithm of the given number (log2(x))
(function)
(C++11)(C++11)(C++11)
natural logarithm (to base e) of 1 plus the given number (ln(1+x))
(function)
(C++11)(C++11)
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
to each element of valarray
(function template)
for log