The log10() function computes the base 10 logarithm of x, log₁₀(x). The value of x must be positive.

Upon successful completion, log10() returns the base 10 logarithm of x.

If x is NaN, NaN is returned. If x is less than 0, -HUGE_VAL or NaN is returned, and errno is set to EDOM. If x is 0, -HUGE_VAL is returned and errno may be set to ERANGE.

For exceptional cases, matherr(3M) tabulates the values to be returned as dictated by Standards other than XPG4.

The log10() function will fail if:

EDOM

The value of x is negative.

The log10() function may fail if:

ERANGE

The value of x is 0.

No other errors will occur.

An application wishing to check for error situations should set errno to 0 before calling log10(). If errno is non-zero on return, or the return value is NaN, an error has occurred.

See attributes(5) for descriptions of the following attributes:

isnan(3M), log(3M), matherr(3M), pow(3M), attributes(5), standards(5)