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 (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 <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>
#include <stdio.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

C23 standard (ISO/IEC 9899:2024):

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

C17 standard (ISO/IEC 9899:2018):

7.12.6.8 The log10 functions (p: 179)
7.25 Type-generic math <tgmath.h> (p: 272-273)
F.10.3.8 The log10 functions (p: 380)

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