External Storage Class in C

[Agustíne]

Hello, Friends. I am working in the multinational company as programmer in C language. I know the C is the basic of all languages but still I don't have the well knowledge of the C language. Because of that I am finding little difficult to work on the C language. So, I just would like to know about the External Storage Class, what is the purpose of the External Storage Class And how they can work. I also want to know that how can I declare External Storage Class. Can anyone is there who can help me?

[absolute55]

Hi, External Storage Class variable is used to give reference to all program files that are visible, of a global variable. External Storage Class variable points the variable name that has been previously defined at storage location. External Storage Class variable can be used when you have the multiple files and defines the function or global variable that is also used in other files, to give the reference of variable that is defined. External Storage Class variable are defined by using the 'extern' keyword.

[Reegan]

The following code of lines staes you that the storage classes and their scope :
#include <stdio.h>
void fun1(void);
void fun2(void);
int glbvar = 10;
int main()
{
printf("\n****storage classes and scope****\n");
glbvar = 20;
printf("\nVariable glbvar, in main() = %d\n", glbvar);
fun1();
printf("\nVariable glbvar, in main() = %d\n", glbvar);
fun2();
printf("\nVariable glbvar, in main() = %d\n", glbvar);
return 0;
}
int glbvar2 = 30;
void fun1(void)
{
char glbvar;
glbvar = 'A';
glbvar2 = 40;
printf("\nIn funct1(), glbvar = %c and glbvar2 = %d\n", glbvar, glbvar2);
}
void fun2(void)
{
double glbvar2;
glbvar = 50;
glbvar2 = 1.234;
printf("\nIn fun2(), glbvar = %d and glbvar2 = %.4f\n", glbvar, glbvar2);
}

[Zecho]

There is another program that helps you to learn about the External Storage Class :
File 1: mainn.c
int cnt=5;
main()
{
write_extern();
}

File 2: writ.c
void write_extern(void);
extern int cnt;
void write_extern(void)
{
printf("count is %i\n", cnt);
}

Now, compile above two files as follows :
gcc main.c write.c -o write