Static in C

Discuss all the details regarding Static variables in C.

Static (and global) variables are initialized during the compile-time, so the initial values will simply be embeded in the executable file itself.

1.static is the default storage class for global variables. The two variables below (count and road) both have a static storage class.

static int Count; int Road; main() { printf("%d\n", Count); printf("%d\n", Road); }

2.'static' can also be defined within a function. If this is done, the variable is initalised at compilation time and retains its value between calls. Because it is initialsed at compilation time, the initalistation value must be a constant.

void Func(void) { static Count=1; }

3.There is one very important use for 'static'. Consider this bit of code.

char *Func(void); main() { char *Text1; Text1 = Func(); } char *Func(void) { char Text2[10]="martin"; return(Text2); }

'Func' returns a pointer to the memory location where 'Text2' starts BUT Text2 has a storage class of auto and will disappear when we exit the function and could be overwritten by something else. The answer is to specify:

static char Text[10]="martin";

The storage assigned to 'Text2' will remain reserved for the duration if the program.

4.The static storage class specifier can only be applied to the following names:

• Objects
• Functions
• Class members
• Anonymous unions

You cannot declare any of the following as static:

• Type declarations
• Function declarations within a block
• Function parameters 

5.The keyword static is the major mechanism in C to enforce information hiding. C++ enforces information hiding through the namespace language feature and the access control of classes.

Note:

Static (becoming global in header files) variables can be defined in .h file. However, their definition should also be provided in the same header file. But , doing this makes the static variable as a private copy of the header file ie it cannot be used elsewhere. In normal cases, this is not intended from a header file.However you should make sure that the header is accepted only once by including #ifndef and #ifdef. By this the compiler will not raise errors saying redefinition of same variable.

#ifndef __static_var_definitions__
#define __static_var_definitions__

static int gblCounter;

#endif