C Programming - Declarations and Initializations - Discussion

#include<stdio.h>
int a;
int a;
int a;//several declarations;
main()
{
printf("%d\n",a);
}
output: 0.
---------------------------------------------------------------------------------------------
#include<stdio.h>
int a;
int a=2;
int a=3;//several definations
main()
{
printf("%d\n",a);

output:user@user:~/c$ cc t.c
t.c:4:5: error: redefinition of \'a\'
t.c:3:5: note: previous definition of \'a\' was here

---------------------------------------------------------------------------------------------
#include<stdio.h>
int a;
int a=2;//single defination
int a;
main()
{
printf("%d\n",a);
}
output: 2.

That means if we use an variable from other file which is globally defined once in that file. Every time when you are using that variable you have do declare that as extern. That means we can declare many times for ones defined global variable.

If we declare a global variable without defining it will stored in bss (uninitialised data section) So, the memory is allocated when we access the data or assign a value to that variable.

Once we declared variable globally then we can access it directly anywhere without declaring it again and again.

Please elaborate with an example, how can a global variable have multiple declarations with one definition only?

Please elaborate with an example. So that I can get it clearly.

Thanks in advance.

But there is no use of declaring it several times even if we can.

It's not cleared. Please explain clearly.

Thanks for your explanation @Venkat.