this will help
->sizeof operator only need declaration not definition.since sizeof operator
calculates size at
compile time.
At compile time code doesnot seek for definition.it only need declaration.if
any variable is declared with extern,it thinks that
its definition will be found at linking time.
In ur question:
1 case. when a =20 is done compiler see that its value is declared.so its OK
.but at link time since def of a is not found
so linker error. since linker tries to find the actual memory address where
the def of a is.
see after compilation the symbol table for a will be as
symbolname| memory location| value
a |find later(garbage)| 20
so there is no problem with compiler .but at link time garbage value need
to be filled with actual memory address
since def is not there so linker error.
case2. there will be noentry in the symbol table for a. as code doesnot
include any defintion related operation.
iF anything helps you, dont forget to say thanks
Thanks
Santosh
On Sun, Jul 3, 2011 at 1:38 AM, HARSH PAHUJA <[email protected]>wrote:
> will ny1 xplain this extern concept....
> y this is a linker error?
>
>
> On Sat, Jul 2, 2011 at 12:49 PM, HARSH PAHUJA <[email protected]>wrote:
>
>> @piyush plz explain how are u getting this......
>>
>>
>> On Sat, Jul 2, 2011 at 12:10 PM, Piyush Sinha
>> <[email protected]>wrote:
>>
>>> i) [Linker error] undefined reference to `a'
>>>
>>> ii) 4
>>>
>>> On 7/3/11, HARSH PAHUJA <[email protected]> wrote:
>>> > 1)
>>> > #include<stdio.h>
>>> > int main()
>>> > {
>>> > extern int a;
>>> > a=20;
>>> > printf("%d",sizeof(a));
>>> > return 0;
>>> > }
>>> >
>>> > 2)
>>> > #include<stdio.h>
>>> > int main()
>>> > {
>>> > extern int a;
>>> > printf("%d",sizeof(a));
>>> > return 0;
>>> > }
>>> >
>>> >
>>> >
>>> > --
>>> > HARSHIT PAHUJA
>>> > M.N.N.I.T.
>>> > ALLAHABAD
>>> >
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>>> >
>>> >
>>>
>>>
>>> --
>>> *Piyush Sinha*
>>> *IIIT, Allahabad*
>>> *+91-8792136657*
>>> *+91-7483122727*
>>> *https://www.facebook.com/profile.php?id=100000655377926 *
>>>
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>>
>>
>> --
>> HARSHIT PAHUJA
>> M.N.N.I.T.
>> ALLAHABAD
>>
>>
>>
>
>
> --
> HARSHIT PAHUJA
> M.N.N.I.T.
> ALLAHABAD
>
>
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