What does static variable mean in C Programming?

What does static variable mean in C Programming?

What does static variable mean in c language with example in C Programming Language ?


 As we have seen, external variables have global scope across the entire program (provided extern declarations are used is files other than where the variable is defined), and a lifetime over the the entire program run. The storage class, static, similarly provides a lifetime over the entire program, however; it provides a way to limit the scope of such variables, Static storage class is declared with the keyword static as the class specifier when the variable is defined. These variables are automatically initialized to zero upon memory allocation just as external variables are. Static storage class can be specified for automatic as well as external variables.
Static automatic variables continue to exist even after the block in which they are defined terminates. Thus, the value of a static variable in a function is retained between repeated function calls to the same function. The scope of static automatic variables is identical to that of automatic variables, i.e. it is local to the block in which it is defined; however, the storage allocated becomes permanent for the duration of the program. Static variables may be initialized in their declarations; however, the initializers must be constant expressions, and initialization is done only once at compile time when memory is allocated for the static variable.

 A function-scope or block-scope variable that is declared as static is visible only within that scope. Furthermore, static variables only have a single instance. In the case of function- or block-scope variables, this means that the variable is not “automatic” and thus retains its value across function invocations.

In computer programming, a static variable is a variable that has been allocated statically—whose lifetime or "extent" extends across the entire run of the program. This is in contrast to the more ephemeral automatic variables (local variables are generally automatic), whose storage is allocated and deallocated on the call stack; and in contrast to objects whose storage is dynamically allocated in heap memory.

When the program (executable or library) is loaded into memory, static variables are stored in the data segment of the program's address space (if initialized), or the BSS segment (if uninitialized), and are stored in corresponding sections of object files prior to loading.

The static keyword is used in C and related languages both for static variables and other concepts.

Scope



In terms of scope and extent, static variables have extent the entire run of the program, but may have more limited scope. A basic distinction is between a static global variable, which has global scope and thus is in context throughout the program, and a static local variable, which has local scope. A static local variable is different from local variable. It is initialized only once no matter how many times that function in which it resides is called. It may be used as a count variable. A static variable may also have module scope or some variant, such as internal linkage in C, which is a form of file scope or module scope.

In object-oriented programming, there is also the concept of a static member variable, which is a "class variable" of a statically defined class – a member variable of a given class which is shared across all instances (objects), and is accessible as a member variable of these objects. Note however that a class variable of a dynamically defined class, in languages where classes can be defined at run time, is allocated when the class is defined and is not static.

Example

An example of static local variable in C:
#include <stdio.h>

void func() {
 static int x = 0; 
 /* x is initialized only once across five calls of func() and
   the variable will get incremented five 
   times after these calls. The final value of x will be 5. */
 x++;
 printf("%d\n", x); // outputs the value of x
}

int main() { //int argc, char *argv[] inside the main is optional in the particular program
 func(); // prints 1
 func(); // prints 2
 func(); // prints 3
 func(); // prints 4
 func(); // prints 5
        return 0;
}



    References



    Learn More :