#include <math.h>float log1pf(float num);double log1p(double num); long double log1pl(long double num);
log1p( ), log1pf( ), and log1pl( ) were added by C99.
The log1p( ) family of functions returns the natural logarithm for num + 1. A domain error occurs if num is negative. If num is –1, a range error is possible.
A related function is log( ).