C++ How to use logb() function and examples

C++ Library Function <cmath>

C ++The logb() function in uses FLT_RADIX as the base of the logarithm and returns the logarithm of |x|.

Generally, FLT_RADIX is2，so for positive values, logb() is equivalent tolog2().

The function is in<cmath>header file is defined.

logb() prototype [from C ++ 11Standard begins]

double logb(double x);
float logb(float x);
long double logb(long double x);
double logb(T x);　//For integer types

The logb() function has only one parameter and returns a value of type double, float, or long double.

logb() parameter

The ilogb() function takes one parameter, whose logb is calculated.

logb() return value

The logb() function uses FLT_RADIX as the base of the logarithm and returns the logarithm of |x|.

If x is zero, it may cause domain error, pole error, or no error, depending on the library implementation.

Example1：The logb() function in C ++How does it work?

#include <iostream>
#include <cmath>
using namespace std;
int　main　()
{
	double x =　121.056, result;
	result = logb(x);
	cout　<<　"logb("　<<　x　<<　")　=　"　<<　"log(|"　<<　x　<<　"|)　=　"<<　result　<<　endl;
	return　0;
}

When running the program, the output is:

logb(121.056)　=　log(|121.056|)　=　6

Example2：An integer type logb() function

#include <iostream>
#include <cmath>
using namespace std;
int　main　()
{
	double　result;
	int　x　=　-5;
	result　=　logb　(x);
	cout　<<　"logb("　<<　x　<<　")　=　"　<<　"log(|"　<<　x　<<　"|)　=　"<<　result　<<　endl;
	return　0;
}

When running the program, the output is:

logb(-5)　=　log(|-5|)　=　2

　 C++ Library Function <cmath>