std::log, std::logf, std::logl

Since C++26

Header: <cmath>

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)

# Declarations

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 );

(since C++11) (constexpr since C++26)

long double logl( long double num );

(since C++11) (constexpr since C++26)

SIMD overload (since C++26)

template< /*math-floating-point*/ V >
constexpr /*deduced-simd-t*/<V>
log ( const V& v_num );

(since C++26)

Additional overloads (since C++11)

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

(constexpr since C++26)

# Parameters

# Return value

If no errors occur, the natural (base-e) logarithm of num (ln(num) or loge(num)) 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(num)).

# Example

#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 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";
}

# See also