The function is defined in <cmath> header file.
[Mathematics] log2x = log2(x) [In C++ Programming]
log2() prototype [As of C++ 11 standard]
double log2(double x); float log2(float x); long double log2(long double x); double log2(T x); // For integral type
The log2() function takes a single argument and returns a value of type double, float or long double.
log2() Parameters
The log2() function takes a single mandatory argument in the range [0, ∞].
If the value is less than zero, log2() returns NaN (Not a Number).
log2() Return value
The log2() function returns the base-2 logarithm of a number.
| Parameter (x) | Return Value |
|---|---|
| x > 1 | Positive |
| x = 1 | Zero |
| 0 > x > 1 | Negative |
| x = 0 | -∞ (- infinity) |
| x < 0 | NaN (Not a Number) |
Example 1: How log2() function works in C++?
#include <iostream>
#include <cmath>
using namespace std;
int main ()
{
double x = 13.056, result;
result = log2(x);
cout << "log2(x) = " << result << endl;
x = -3.591;
result = log2(x);
cout << "log2(x) = " << result << endl;
return 0;
}
When you run the program, the output will be:
log2(x) = 3.70664 log2(x) = nan
Example 2: log2() function with integral type
#include <iostream>
#include <cmath>
using namespace std;
int main ()
{
double result;
int x = 2201;
result = log2(x);
cout << "log2(" << x << ") = " << result << endl;
return 0;
}
When you run the program, the output will be:
log2(2201) = 11.1039