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Showing content from http://en.cppreference.com/w/cpp/language/../numeric/math/log.html below:

std::log, std::logf, std::logl - cppreference.com

(1) float       log ( float num );

double      log ( double num );

long double log ( long 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)

long double logl( long double num );

(3) (since C++11)
(constexpr since C++26) template< /*math-floating-point*/ V >

constexpr /*deduced-simd-t*/<V>

            log ( const V& v_num ); (S) (since C++26)

template< class Integer >
double      log ( Integer num );

(A) (constexpr since C++26) 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 treated as double.

(since C++11) [edit] Parameters num - floating-point or integer value [edit] 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_VAL, -HUGE_VALF, or -HUGE_VALL is returned.

[edit] 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),

[edit] 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)).

[edit] Example

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
[edit] See also computes common (base 10) logarithm (\({\small\log_{10}{x}}\)log10(x))
(function) [edit] base 2 logarithm of the given number (\({\small\log_{2}{x}}\)log2(x))
(function) [edit] natural logarithm (to base e) of 1 plus the given number (\({\small\ln{(1+x)}}\)ln(1+x))
(function) [edit] returns e 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 function std::log to each element of valarray
(function template) [edit]

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