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static variable in c

static keyword in c:

Keyword static is used for declaring static variables in

c. This modifier is used with all data types like int, float,

double, array, pointer, structure, function etc.

Important points about static keyword:

1. It is not default storage class of global variables. For

example, analyze the following three programs and its output.

(a)

#include<stdio.h>

int a;

int main()

printf("%d",a);

return 0;

Output: 0

(b)

#include<stdio.h>

static int a;

int main()

printf("%d",a);

return 0;

Output: 0

(c)

#include<stdio.h>

extern int a;

int main()

printf("%d",a);

return 0;

Output: Compilation error

At first glance if you will observe the output of above three

codes you can say default storage class of global variable is

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static. But it is not true. Why? Read extern storage class.

2. Default initial value of static integral type variables are

zero otherwise null. For example:

#include <stdio.h>

static char c;

static int i;

static float f;

static char *str;

int main()

printf("%d %d %f %s",c,i,f,str);

return 0;

Output: 0 0 0.000000 (null)

3. A same static variable can be declared many times but we

can initialize at only one time. For example:

(a)

#include <stdio.h>

static int i; //Declaring the variable i.

static int i=25; //Initializing the variable.

static int i; //Again declaring the variable i.

int main()

static int i; //Again declaring the variable i.

printf("%d",i);

return 0;

Output: 25

(b)

#include <stdio.h>

static int i; //Declaring the variable

static int i=25; //Initializing the variable

int main()

printf("%d",i);

return 0;

static int i=20; //Again initializing the variable

Output: Compilation error: Multiple initialization variable i.

4. We cannot write any assignment statement globally. For

example:#include <stdio.h>

static int i=10; //Initialization statement

i=25; //Assignment statement

int main()

printf("%d",i);

return 0;

Output: Compilation error

Note: Assigning any value to the variable at the time of

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declaration is known as initialization while assigning any

value to variable not at the time of declaration is known

assignment.

(b)

#include <stdio.h>

static int i=10;

int main()

i=25; //Assignment statement

printf("%d",i); return 0;

Output: 25

(5) A static variable initializes only one time in whole

program. For example:

#include <stdio.h>

static int i=10;

int main()

i=5;

for(i=0;i<5;i++)

static int a=10; //This statement will execute

//only time.

printf("%d",a++);//This statement will execute

//five times.

return 0;

Output: 10 11 12 13 14

(6)If we declared static variable locally then its visibility

will within a block where it has declared. For example:

#include<stdio.h>

int main()

static int a=5;

printf("%d",a);

//printf("%d",a); variable a is not visible here.

return 0;

Output: 5

7. If declared a static variable or function globally then its

visibility will only the file in which it has declared not in

the other files. For example:

(a)

#include<stdio.h>

static float a=144.0f; //global to all function

int main()

printf("%d",a); //variable a is visible here.

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//printf("%d",b); variable b is not visible here.

printf("%d",a); //variable a is visible here.

//printf("%d",b); variable b is not visible here.

return 0;

static int b=5; //Global to only calculation function

void calculation()

printf("%d",a); //variable a is visible here.

printf("%d",b); //variable b is visible here.

(b) Consider a c program which has written in two files named

as one.c and two.c:

//one.c

#include<conio.h>

static int i=25;

static int j=5;

void main() clrscr();

sum();

getch();

//two.c

#include<stdio.h>

extern int i; //Declaration of variable i.

extern int j; //Declaration of variable j.

/**

Above two lines will search the initialization statement of

variable i and j either in two.c (if initialized variable is

static or extern) or one.c (if initialized variable is

extern)

*/

extern void sum()

int s;

s=i+j;

printf("%d",s);

Compile and execute above two file one.c and two.c at the same

time:

In Turbo c compiler

Step 1: Write above two codes in the file named as one.c and

two.c (You can give any name as you like) and save it.

Step 2: In Turbo c++ IDE click on Project -> Open project menu

as shown in following screen dump.

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Step 3: After Clicking on open project you will get following

screen:

In Open project File text field write any project name with

.prj extension. In this example I am writing project name as

CProject.PRJ. Now press OK button.

Step 4: After pressing OK button you will get following

screen:

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Now click on Project -> Add item menu.

Step 5: After clicking Add item you will get following screen:

In the name text field write down all c source code file one

by one i.e. first write one.c and click on Add button

Then write two.c and click on Add button and so on

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Step 6: At the end click on Done button. After clicking on

done button you will get following screen:

At the lower part of window you can see project name, list of

files you have added etc.

Step7: To compile the two files press Alt+F9 and to run the

above program press Ctrl+F9

Note: To close the project click on Project -> Close project.

Output: Compilation error: Unknown symbol i and j.

Hence we can say variable i and j which has initialized into

two.c is not visible in file one.c. This example proves

visibility of globally declared static variable is file.

Note: In the above example function sum which was declared and

defined in two.c has also storage class extern. So we can call

from other file (one.c).If it will static then we cannot call

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function sum since static storage class is only visible to the

file where it has declared.

(8)If we static variable has declared locally or globally its

scope will always whole the program. For example:

(a) //locally declaration of static variable

#include<stdio.h>

void visit();

int main()

int i=0;

//Opening inner block

static int a=5; //locally declaration

XYZ:; //Label of goto statement

printf("%d ",a);

a++;

i++;

//closing inner block.

visit();

/* printf("%d",a); Variable a is not visible here but

it is alive. */ if(i<5)

goto XYZ;

return 0;

void visit()

Output: 5 6 7 8 9

Explanation: When program control will come out of inner block

where variable a has declared then outside of inner block

variable a is not visible but its scope is outside the program

i.e. variable a hasn’t dead .If with help of goto statement

control again comes inside the inner block it prints previous

incremented values which was not possible in case of auto or

register variables.

(b)

//Locally declarations of variable

There are two c source code files:

//one.c

#include<stdio.h>

#include<conio.h>

void main()

int i;

for(i=0;i<3;i++)

static int a=5;

printf("%d\n",a);

a++;

visit();

getch();

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//two.c

#include<stdio.h>

void visit()

printf("Don’t disturb, I am learning storage class");

/* printf("%d",a); Variable a is not visible here but

It is alive. */

Now compile and execute both files together:Output:

5

disturb, I am learning storage class

6

disturb, I am learning storage class

7

disturb, I am learning storage class

Explanation: When control goes to another file and comes even

that variable didn’t dead and it prints previous incremented

value.

Note: In both examples if you will declare static variableglobally you will get same output.

9. A static variables or functions have internal linkage. An

internal linkage variables or functions are visible to the

file where it has declared.

Introduction

auto

register

static

extern

C tutorial home.

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Replies

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21 comments:

Aarti 2/18/11, 12:11 AM

explanation is just fab.

Reply

akash rai 8/5/15, 10:10 PM

But concepts are wrong... pls try to execute the prg your self u will find lots of error

Anonymous 6/16/11, 12:23 PM

In 8th point (b)part,you have called visit in one.c file but in two.c file you have not declared the extern keyword

before its defination...can u plz tel me why?

Reply

Anonymous 8/6/11, 1:46 PM

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Reply

in the 8th point we r learning the scope of static at out side of the files..

Reply

Anonymous 9/21/11, 3:24 PM

in the 8th point the visit() function must be declared extern in two.c .....correct me if i am wrong..??

Reply

Simas A. 6/16/14, 4:59 PM

All functions have extern as the default storage class, so no you don't need to write it.

dinhpq 10/13/11, 11:14 PM

Thanks.

Reply

Anonymous 11/18/11, 1:08 PM

reaaly nice 1....commendable

Reply

ranjith 1/2/12, 4:59 PM

#include

static int i; //Declaring the variable i.

static int i=25; //Initializing the variable.

static int i; //Again declaring the variable i.

int main()

static int i; //Again declaring the variable i.

printf("%d",i);

return 0;

Output: 25

her if we compile output we should get 0 only ..becz in main block locally i of course static is not initialised...so

it intialissed by default as zero....comparing local and global local variable got more preference than global

static variable(i=25)..so compulsory we will get zero as output....

plz comment to this comment ..to conform it correct analysis or not

Reply

Anitha Venkatesan 1/26/13, 3:16 AM

Ya thats correct actually it gives output as o.

Vijai 2/11/14, 9:05 PM

Yes you are correct in gcc I do get the same.

vijay

urvinder 2/25/12, 1:38 AM

i checked in vc++,it gives the error while compiling /**error 'i' : redefinition; different storage class**/

Reply

Anonymous 2/25/13, 8:58 PM

that was a complete tutorial!! thanks brother!!

Reply

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Atiqur Rahman 4/7/13, 11:11 AM

Reply

SALIL AGRAWAL 12/24/13, 12:02 PM

Similar Article see if it makes sense

Static Variables in C

Reply

karthik nayak 5/19/14, 7:29 PM

brilliant explanation :D

Reply

pravin 9/2/14, 11:22 AM

yes correct

Reply

Amit Kumar 2/22/15, 3:34 PM

Why its giving output as : 43

Can anyone please explain it to me?

Thanx in advance ?

#include

static int i; //Declaring the variable i.

static int i=25; //Initializing the variable.

static int i; //Again declaring the variable i.

int main()

int i; //Again declaring the variable i.

printf("%d",i);

return 0;

Reply

Nóra Vörös 3/4/15, 5:59 PM

int i; //Again declaring the variable i.

There is no static keyword in front of the declaration. It is "another" i, an automatic, uninitialized i.

The content of the memory area where it is placed is accidentally 43.

Raj Naik 6/15/15, 3:02 PM

3. A same static variable can be declared many times but we can initialize at only one time. For example:

(a)

#include

static int i; //Declaring the variable i.

static int i=25; //Initializing the variable.

static int i; //Again declaring the variable i.

int main()

static int i; //Again declaring the variable i.

printf("%d",i);

return 0;

Output: 25

Here Output should be zero, not 25.

Reply

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Meenu Rajput 7/31/15, 10:32 AM

Here, it gives an output 25 but not zero because it has been initialized as 25 although it has been declared

again as a local variable.

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