In computer programming, static variables data value persists for the life of the running process and typically have a broader scope than other variables. Their values may be set at run-time or may change subtly during program execution. The terminology is C and C++ based, but also used in many derived programming languages, in languages with different heritage the same concept may instead be called global variables.
Computer programs may store constants in constant variables or in static variables, depending on the available features of the programming language. For example, a program that uses an approximation of pi might be easier to write, read, and maintain with a variable called "PI" instead of multiple occurrences of "3.14159"
In the C programming language, static is used with global variables and functions to set their scope to the containing file. In local variables, static is used to store the variable in the statically allocated memory instead of the automatically allocated memory. While the language does not dictate the implementation of either type of memory, statically allocated memory is typically reserved in data segment of the program at compile time, while the automatically allocated memory is normally implemented as a transient call stack.
For local variables
Most programming languages include the feature of subroutines. Variables local to subroutines (local variables) are usually created and destroyed within the subroutine itself (so-called automatic variables). Some languages, however, (e.g., the C programming language) allow subroutines to retain the value of variables between calls, so that the function can preserve its state if necessary. For example, a static variable can record the number of times its subroutine has been executed. Doing so is otherwise possible using global variables or external storage, like a file on disk.
For class variables
Object-oriented programming languages use classes and objects. In this case, a class variable means a variable that is not associated with instances of the class. There is exactly one copy of the variable that is shared among methods of all instances no matter how many or how few instances exist. In C++, class variables are known as static data members.
In this sample, count applies to the class while url applies to each instance. Note that the count variable must be initialized outside the class.