A static local variable causes the compiler to create permanent storage for it in much the same way that it does for a global variable.
#include <stdio.h>
#include <conio.h>
int count(int i);
int main(void)
{
do {
count(0);
} while(!kbhit());
printf("count called %d times", count(1));
return 0;
}
int count(int i)
{
static int c=0;
if(i) return c;
else c++;
return 0;
}Initialize static member field outside the class declaration
#include <iostream>
using std::cout;
using std::endl;
class Box {
public:
Box() {
cout << "Default constructor called" << endl;
++objectCount;
length = width = height = 1.0;
}
Box(double lvalue, double wvalue, double hvalue) :
length(lvalue), width(wvalue), height(hvalue) {
cout << "Box constructor called" << endl;
++objectCount;
}
double volume() const {
return length * width * height;
}
int getObjectCount() const {return objectCount;}
private:
static int objectCount;
double length;
double width;
double height;
};
int Box::objectCount = 0;
int main() {
cout << endl;
Box firstBox(17.0, 11.0, 5.0);
cout << "Object count is " << firstBox.getObjectCount() << endl;
Box boxes[5];
cout << "Object count is " << firstBox.getObjectCount() << endl;
cout << "Volume of first box = "
<< firstBox.volume()
<< endl;
const int count = sizeof boxes/sizeof boxes[0];
cout <<"The boxes array has " << count << " elements."
<< endl;
cout <<"Each element occupies " << sizeof boxes[0] << " bytes."
<< endl;
for(int i = 0 ; i < count ; i++)
cout << "Volume of boxes[" << i << "] = "
<< boxes[i].volume()
<< endl;
return 0;
}Box constructor called
Object count is 1
Default constructor called
Default constructor called
Default constructor called
Default constructor called
Default constructor called
Object count is 6
Volume of first box = 935
The boxes array has 5 elements.
Each element occupies 24 bytes.
Volume of boxes[0] = 1
Volume of boxes[1] = 1
Volume of boxes[2] = 1
Volume of boxes[3] = 1
Volume of boxes[4] = 1
Use static variable to compute a running average of numbers entered by the user
#include <iostream>
using namespace std;
int f(int i);
int main()
{
int num;
do {
cout << "Enter numbers (-1 to quit): ";
cin >> num;
if(num != -1)
cout << "average is: " << f(num) << "\n";
} while(num > -1);
return 0;
}
int f(int i)
{
static int sum = 0, count = 0;
sum = sum + i;
count++;
return sum / count;
}Enter numbers (-1 to quit): 1
average is: 1
Enter numbers (-1 to quit): 2
average is: 1
Enter numbers (-1 to quit): 3
average is: 2
Enter numbers (-1 to quit): 2
average is: 2
Enter numbers (-1 to quit): 1
average is: 1
Enter numbers (-1 to quit): 2
average is: 1
Enter numbers (-1 to quit): 3
average is: 2
Enter numbers (-1 to quit): -1
Using a static long variable
#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;
long next();
int main() {
for(int i = 0 ; i < 30 ; i++) {
cout << std::setw(12) << next ();
}
cout << endl;
return 0;
}
long next () {
static long last = 0;
last = last + 1;
return last;
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