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| Nearest integer floating point operations | |||||||||||||||||||||||||||||||||||||||||
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| Floating point manipulation functions | |||||||||||||||||||||||||||||||||||||||||
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Defined in header <cmath> | ||
| (1) | ||
float log(float num); double log(double num); | (until C++23) | |
/*floating-point-type*/ log(/*floating-point-type*/ num); | (since C++23) (constexpr since C++26) | |
float logf(float num); | (2) | (since C++11) (constexpr since C++26) |
longdouble logl(longdouble num); | (3) | (since C++11) (constexpr since C++26) |
SIMD overload(since C++26) | ||
Defined in header <simd> | ||
template</*math-floating-point*/ V> constexpr/*deduced-simd-t*/<V> | (S) | (since C++26) |
Additional overloads(since C++11) | ||
Defined in header <cmath> | ||
template<class Integer> double log( Integer num); | (A) | (constexpr since C++26) |
std::log for all cv-unqualified floating-point types as the type of the parameter.(since C++23)S) The SIMD overload performs an element-wise std::log onv_num.
| (since C++26) |
A) Additional overloads are provided for all integer types, which are treated asdouble. | (since C++11) |
Contents |
| num | - | floating-point or integer value |
If no errors occur, the natural (base-e) logarithm ofnum (ln(num) orloge(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.
Errors are reported as specified inmath_errhandling.
Domain error occurs ifnum is less than zero.
Pole error may occur ifnum is zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
The additional overloads are not required to be provided exactly as(A). They only need to be sufficient to ensure that for their argumentnum of integer type,std::log(num) has the same effect asstd::log(static_cast<double>(num)).
#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 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) = 0base-5 logarithm of 125 = 3log(1) = 0log(+Inf) = inflog(0) = -inf errno == ERANGE: Numerical result out of range FE_DIVBYZERO raised
(C++11)(C++11) | computes common (base10) logarithm (\({\small\log_{10}{x}}\)log10(x)) (function)[edit] |
(C++11)(C++11)(C++11) | base2 logarithm of the given number (\({\small\log_{2}{x}}\)log2(x)) (function)[edit] |
(C++11)(C++11)(C++11) | natural logarithm (to basee) of1 plus the given number (\({\small\ln{(1+x)}}\)ln(1+x)) (function)[edit] |
(C++11)(C++11) | returnse raised to the given power (\({\small e^x}\)ex) (function)[edit] |
| complex natural logarithm with the branch cuts along the negative real axis (function template)[edit] | |
| applies the functionstd::log to each element of valarray (function template)[edit] | |
C documentation forlog | |
