log10, log10f, log10l - cppreference.com (original) (raw)

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.

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.

[edit] Parameters

arg	-	floating-point value

[edit] 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.

[edit] 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.

[edit] 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

[edit] 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

[edit] See also

| | computes natural (base-e) logarithm (\({\small \ln{x} }\)ln(x)) (function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | computes base-2 logarithm (\({\small \log_{2}{x} }\)log2(x)) (function) [edit] | | | computes natural (base-e) logarithm of 1 plus the given number (\({\small \ln{(1+x)} }\)ln(1+x)) (function) [edit] | | |