Static Variables
Static variables in a Function: When a variable is declared as static, space for it gets allocated for the lifetime of the program. Even if the function is called multiple times, space for the static variable is allocated only once and the value of the variable in the previous call gets carried through the next function call. This is useful for implementing coroutines in C/C++ or any other application where the previous state of function needs to be stored.
C++
// C++ program to demonstrate// the use of static Static// variables in a Function#include <iostream>#include <string>using namespace std;void demo(){ // static variable static int count = 0; cout << count << " "; // value is updated and // will be carried to next // function calls count++;}int main(){ for (int i = 0; i < 5; i++) demo(); return 0;} |
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You can see in the above program that the variable count is declared static. So, its value is carried through the function calls. The variable count is not getting initialized every time the function is called. As a side note, Java doesn’t allow static local variables in functions.
Static variables in a class: As the variables declared as static are initialized only once as they are allocated space in separate static storage so, the static variables in a class are shared by the objects. There can not be multiple copies of the same static variables for different objects. Also because of this reason static variables can not be initialized using constructors.
C++
// C++ program to demonstrate static// variables inside a class#include <iostream>using namespace std;class GfG {public: static int i; GfG(){ // Do nothing };};int main(){ GfG obj1; GfG obj2; obj1.i = 2; obj2.i = 3; // prints value of i cout << obj1.i << " " << obj2.i;} |
Output
undefined reference to `GfG::i' collect2: error: ld returned 1 exit status
You can see in the above program that we have tried to create multiple copies of the static variable i for multiple objects. But this didn’t happen. So, a static variable inside a class should be initialized explicitly by the user using the class name and scope resolution operator outside the class as shown below:
C++
// C++ program to demonstrate static// variables inside a class#include <iostream>using namespace std;class GfG {public: static int i; GfG(){ // Do nothing };};int GfG::i = 1;int main(){ GfG obj; // prints value of i cout << obj.i;} |
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Static Keyword in C++
Prerequisite: Static variables in C
The static keyword has different meanings when used with different types. We can use static keywords with:
- Static Variables: Variables in a function, Variables in a class
- Static Members of Class: Class objects and Functions in a class Let us now look at each one of these uses of static in detail.