In this C++ tutorial, you will learn how to find logarithm of absolute value of given number using logb() function of cmath, with syntax and examples.
C++ logb()
C++ logb() returns logarithm of absolute value of given argument. FLT_RADIX is used as base for the logarithm calculation.
FLT_RADIX is 2 or greater, but generally 2. Please check this value before using logb() function.
Syntax
The syntax of C++ logb() is
logb(x)
where
| Parameter | Description |
|---|---|
| x | A double, float, long double, or any integral type value. |
Returns
The return value depends on the type of value passed for parameter x.
The return value of logb(x) is
- double if x is double or integral type.
- float if x is float.
- long double if x is long double.
The synopsis of logb() function is
double logb(double x); float logb(float x); long double logb(long double x); double logb(T x); // for integral type argument values
logb() is a function of cmath library. Include cmath library at the start of program, if using logb() function.
Example
In this example, we read a value from user into variable x, and find the logarithm value of |x| using logb() function.
C++ Program
#include <iostream>
#include<cmath>
using namespace std;
int main() {
double x;
cout << "Enter a number : ";
cin >> x;
double result = logb(x);
cout << "logb(" << x << ") : " << result << endl;
} Output
Enter a number : 16 logb(16) : 4 Program ended with exit code: 0
Enter a number : -16 logb(-16) : 4 Program ended with exit code: 0
Enter a number : 0 logb(0) : -inf Program ended with exit code: 0
Conclusion
In this C++ Tutorial, we learned the syntax of C++ logb(), and how to use this function to find the logarithm of absolute value of given number, with base value of FLT_RADIX, with the help of examples.