std::log, std::logf, std::logl - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| (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) |
| SIMD overload (since C++26) | ||
| Defined in header | ||
| template< /*math-floating-point*/ V > constexpr /*deduced-simd-t*/<V> log ( const V& v_num ); | (S) | (since C++26) |
| Additional overloads (since C++11) | ||
| Defined in header | ||
| 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),
- 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.
[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
| log10log10flog10l(C++11)(C++11) | computes common (base 10) logarithm (\({\small\log_{10}{x}}\)log10(x)) (function) [edit] |
|---|---|
| log2log2flog2l(C++11)(C++11)(C++11) | base 2 logarithm of the given number (\({\small\log_{2}{x}}\)log2(x)) (function) [edit] |
| log1plog1pflog1pl(C++11)(C++11)(C++11) | natural logarithm (to base e) of 1 plus the given number (\({\small\ln{(1+x)}}\)ln(1+x)) (function) [edit] |
| expexpfexpl(C++11)(C++11) | returns e raised to the given power (\({\small e^x}\)ex) (function) [edit] |
| log(std::complex) | complex natural logarithm with the branch cuts along the negative real axis (function template) [edit] |
| log(std::valarray) | applies the function std::log to each element of valarray (function template) [edit] |
| C documentation for log |