C Programming - Declarations and Initializations - Discussion

@All.

According to me, the coding is;

#include<stdio.h>
int main()
{
extern int i;
printf("\n%d",sizeof(i));
return 0;
}
int i=20;

So, the reason the program will show linkage error is:

-> extern int i; (which is an EXTERNAL LINKAGE is a declaration that says that there exists a variable 'i' in some other program but it does not define it in the current program.. the variable will come into existence only when it is defined in the program. Until then, it is virtually declared and does not exist in the program. Thus, it shows the error 'UNDEFINED SYMBOL 'i'.

If you declare the extern int i; it will not allocate memory, when you define extern int i=0; it will allocate memory.

@All.

As per my knowledge;

is extern int a - local or global variable or something else? and also in answer int a=20 is referred as a local variable but it should be a global variable.

So what happens when there is a conflict when between extern and global variable defined below :
#include<stdio.h>
int main()
extern int a;
int a=20;
{

printf("%d\n", sizeof(a));
return 0;
}

I guess it should give priority to int a=20, but what will happen when there is no conflict who will get the preference extern int a OR int a=20?

#include<stdio.h>
int main()
{
extern int a;
printf("%d\n", sizeof(a));
return 0;
}

Please explain me the output.

Why we use sizeof() what purpose to use?

extern int i means global variable that means it can move anywhere. So it has to print the size of i. If I am wrong then explain that.

i is already defined how can it be said that it is not defined?

Guys, I don't know how turbo C on 16 bit platform worked, but I know this should show 2, not error. Also, if this this should trigger an error, then you should provide the compilation or linkage line. Try this on any decent compiler like gcc and then fix the question.

Can someone briefly explain me about linkin error and enum with eg ?