log

 

C

Language

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

 

Common mathematical functions

Functions
Basic operations
abs labs llabs imaxabs (C99) fabs div ldiv lldiv imaxdiv (C99) fmod	remainder (C99) remquo (C99) fma (C99) fmax (C99) fmin (C99) fdim (C99) nan nanf nanl (C99) (C99) (C99)
Exponential functions
exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
Power functions
sqrt cbrt (C99)	hypot (C99) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C99) acosh (C99) atanh (C99)
Error and gamma functions
erf (C99) erfc (C99)	lgamma (C99) tgamma (C99)
Nearest integer floating point operations
ceil floor round lround llround (C99) (C99) (C99)	trunc (C99) nearbyint (C99) rint lrint llrint (C99) (C99) (C99)
Floating point manipulation functions
ldexp scalbn scalbln (C99) (C99) ilogb (C99) logb (C99)	frexp modf nextafter nexttoward (C99) (C99) copysign (C99)
Classification
fpclassify (C99)
isfinite (C99)
isinf (C99)
isnan (C99)
isnormal (C99)
signbit (C99)
Macro constants
HUGE_VALF HUGE_VAL HUGE_VALL (C99) (C99)	FP_NORMAL FP_SUBNORMAL FP_ZERO FP_INFINITE FP_NAN (C99) (C99) (C99) (C99) (C99)

 

Defined in header <math.h>
float       logf( float arg );		(since C99)
double      log( double arg );
long double logl( long double arg );		(since C99)

Computes the natural (base e) logarithm of arg.

Parameters

arg

-

floating point value

Return value

Natural logarithm of arg.

Domain error occurs if arg is negative. NAN is returned in that case.

Range error occurs if arg is ​0​. -HUGE_VAL is returned in that case.

See also

exp	returns e raised to the given power (ex) (function)
log10	computes common (base 10) logarithm (log10(x)) (function)
pow	raises a number to the given power (xy) (function)
C++ documentation for log