c - static variables -

January 15, 2015

can explain when static variables should used , why?

there 2 distinct uses of static keyword in c:

static declarations in function's scope
static declarations outside of function's scope

(mostly) evil: static variables in function

a static variable in function used "memory" state.

basically, variable initialized default value first time call it, , retains previous value in future calls.

it potentially useful if need remember such state, use of such statics frowned upon because pretty global variables in disguise: consume memory until termination of process once.

so, in general, making localized functions evil / bad.

example:

#include <stdio.h>   void  ping() {   static int counter = 0;    return (++counter); }  int   main(int ac, char **av) {   print("%d\n", ping()); // outputs 1   print("%d\n", ping()); // outputs 2   return (0); }

output:

1 2

(mostly) good: static variables outside of function's scope

you can use static outside of function on variable or function (which, after all, sort of variable , points memory address).

what limit use of variable file containing it. cannot call somewhere else. while still means that function/var "global" in sense consumes memory until program's termination, @ least has decency not pollute "namespace".

this interesting because way can have small utility functions identical names in different files of project.

so, in general, making localized functions good.

example:

example.h

#ifndef __example_h__ # define __example_h__  void  function_in_other_file(void);  #endif

file1.c

#include <stdio.h>  #include "example.h"  static void  test(void);   void test(void) {   printf("file1.c: test()\n"); }  int   main(int ac, char **av) {   test();  // calls test function declared above (prints "file1.c: test()")   function_in_other_file();   return (0); }

file2.c

#include <stdio.h>  #include "example.h"  static void  test(void); // that's different test!!   void test(void) {   printf("file2.c: test()\n"); }  void   function_in_other_file(void) {   test();  // prints file2.c: test()   return (0); }

output:

file1.c: test() file2.c: test()

ps: don't start throwing stones @ me if you're purist: know static vars not evil, they're not globals either, functions not variables, , there's no actual "namespace" (don't started on symbols) in c. that's sake of explanation here.

Search This Blog

shell