Difference between revisions of "cpp/numeric/math/log10"

Revision as of 20:01, 17 October 2018

Parameters

Return value

If no errors occur, the common (base-10) logarithm of arg (log10(arg) or lg(arg)) 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.

Error handling

Errors are reported as specified in math_errhandling

Domain error occurs if arg is less than zero.

Pole error may occur if arg 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

Example

#include <iostream>
#include <cmath>
#include <cerrno>
#include <cstring>
#include <cfenv>
#pragma STDC FENV_ACCESS ON
int main()
{
    std::cout << "log10(1000) = " << std::log10(1000) << '\n'
              << "log10(0.001) = " << std::log10(0.001) << '\n'
              << "base-5 logarithm of 125 = " << std::log10(125)/std::log10(5) << '\n';
    // special values
    std::cout << "log10(1) = " << std::log10(1) << '\n'
              << "log10(+Inf) = " << std::log10(INFINITY) << '\n';
    // error handling 
    errno=0; std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "log10(0) = " << std::log10(0) << '\n';
    if(errno == ERANGE)
        std::cout << "    errno == ERANGE: " << std::strerror(errno) << '\n';
    if(std::fetestexcept(FE_DIVBYZERO))
        std::cout << "    FE_DIVBYZERO raised\n";
}

log10(1000) = 3
log10(0.001) = -3
base-5 logarithm of 125 = 3
log10(1) = 0
log10(+Inf) = inf
log10(0) = -inf
    errno == ERANGE: Numerical result out of range
    FE_DIVBYZERO raised

See also