doubt in storage class

[jeyshree]

Hai,
I am jeyshree.W ill anyone please explain me when is the memory allocated for gloabal variable in the following snippets?
#include<stdio.h>
#include<conio.h>
extern int a;
main()
{
printf("%d",a) ;
getch();
}
int a=10;
OUTPUT:
10
and another one:
#include<stdio.h>
#include<conio.h>
extern int a=10;
main()
{
printf("%d",a) ;
getch();
}
OUTPUT:
10
Please explain .Thanks in advance

[donbock]

"when is memory allocated"

Are you looking for an answer that is true for typical compiler implementations or are you interested in only what is guaranteed by the C Standard?

It would help me understand what you're asking for if you listed some of the possible options you can think of for when memory might be allocated.

[weaknessforcats]

Memory for global variables is allocated before main() starts.

This is a global variable:

extern int val = 10;

This is not:

extern int val;

The first case creates a global variable with an intial value of 10 and the variable has external linkage.

The second case tells the compiler that there is a variable named val that has external linkage but it's not in this file.

[donbock]

In the following example, the extern statement serves only one purpose -- it allows a to be accessed from the main function. Without the extern statement, references to a from main would be forward references to line 5, which are not permitted in C. Line 1 could be deleted without altering the operation of the program if line 5 were moved to that position.

extern int a;
int main() {
   ...
   }
int a = 10;

In the following example, the extern keyword is superfluous. There would be no change to the operation of the program if it were removed.

extern int a = 10;