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log10, log10f, log10l

Defined in header `<math.h>`
float log10f( float arg );	(1)	(since C99)
double log10( double arg );	(2)
long double log10l( long double arg );	(3)	(since C99)
Defined in header `<tgmath.h>`
#define log10( arg )	(4)	(since C99)

1-3) Computes the common (base-10) logarithm of arg.

4) Type-generic macro: If arg has type long double, log10l is called. Otherwise, if arg has integer type or the type double, log10 is called. Otherwise, log10f is called.

Parameters

arg

floating point value

Return value

If no errors occur, the common (base-10) logarithm of arg (log
10(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 <stdio.h>
#include <math.h>
#include <float.h>
#include <errno.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
int main(void)
{
    printf("log10(1000) = %f\n", log10(1000));
    printf("log10(0.001) = %f\n", log10(0.001));
    printf("base-5 logarithm of 125 = %f\n", log10(125)/log10(5));
    // special values
    printf("log10(1) = %f\n", log10(1));
    printf("log10(+Inf) = %f\n", log10(INFINITY));
    //error handling
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("log10(0) = %f\n", log10(0));
    if(errno == ERANGE) perror("    errno == ERANGE");
    if(fetestexcept(FE_DIVBYZERO)) puts("    FE_DIVBYZERO raised");
}

Possible output:

log10(1000) = 3.000000
log10(0.001) = -3.000000
base-5 logarithm of 125 = 3.000000
log10(1) = 0.000000
log10(+Inf) = inf
log10(0) = -inf
    errno == ERANGE: Numerical result out of range
    FE_DIVBYZERO raised

References

C11 standard (ISO/IEC 9899:2011):

7.12.6.8 The log10 functions (p: 245)
7.25 Type-generic math <tgmath.h> (p: 373-375)
F.10.3.8 The log10 functions (p: 522)

C99 standard (ISO/IEC 9899:1999):

7.12.6.8 The log10 functions (p: 225-226)
7.22 Type-generic math <tgmath.h> (p: 335-337)
F.9.3.8 The log10 functions (p: 459)

C89/C90 standard (ISO/IEC 9899:1990):

4.5.4.5 The log10 function