c99 [ flag... ] file... –lm [ library... ] #include <math.h> double log10(double x);
float log10f(float x);
long double log10l(long double x);
These functions compute the base 10 logarithm of x, log10(x).
Upon successful completion, log10() returns the base 10 logarithm of x.
If x is ±0, a pole error occurs and log10(), log10f(), and log10l() return −HUGE_VAL, −HUGE_VALF, and −HUGE_VALL, respectively.
For finite values of x that are less than 0, or if x is −Inf, a domain error occurs and a NaN is returned.
If x is NaN, a NaN is returned.
If x is 1, +0 is returned.
If x is +Inf, x is returned.
For exceptional cases, matherr(3M) tabulates the values to be returned by log10() as specified by SVID3 and XPG3.
These functions will fail if:
The finite value of x is negative, or x is -Inf.
If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception is raised.
The log10() function sets errno to EDOM if the value of x is negative.
The value of x is 0.
If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the divide-by-zero floating-point exception is raised.
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.
An application can also set errno to 0 before calling log10(). On return, if errno is non-zero, an error has occurred. The log10f() and log10l() functions do not set errno.
See attributes(5) for descriptions of the following attributes:
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feclearexcept(3M), fetestexcept(3M), isnan(3M), log(3M), math.h (3HEAD), matherr(3M), pow(3M), attributes(5), standards(5)