Compiler's calculation on memory/address

[vermarajeev]

Hello All,
How is an address being calculated by the compiler? or what does the compiler do internally when I write the following:
For example:
When I say

int a;

int a;

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some memory is allocated with some address by the compiler. My question is how?
As per my understanding, the compiler takes the sizeof datatype which is "int" in above case and then does some manipulation to calculate the address which is a part of memory?

Can someone please clear me about this?

Thanks in advance.

[Michiel]

You're allocating an int as a local variable on the stack. Take a look at this. For each variable (local and parameter) the compiler knows the offset from the frame pointer.

[vermarajeev]

You're allocating an int as a local variable on the stack. Take a look at this. For each variable (local and parameter) the compiler knows the offset from the frame pointer.

The link tells only about the call stack. My question was how does the compiler calculate the address of a variable? I mean,

For example:

int main()
{
   int a = 10;
   cout<<&a<<endl;
}

int main()
{
   int a = 10;
   cout<<&a<<endl;
}

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On my system the address is 0012FED4.
I want to know how is the address "0012FED4" calculated by the compiler? Any idea...

Thanks

[wysota]

It's exactly as Michiel said. "a" is placed as the first (or second, or third) variable on the stack. There is a register that holds the current frame pointer that points to the beginning of the stack frame. The frame contains things like the return address and the previous frame pointer. After that local variables (your "a" included) are placed. So the compiler knows, that to reference "a" it has to go to the address pointed by "FP" (frame pointer) and substract (or add, depending on the architecture) for instance "12". Every time you reference "a", the compiler changes that to "$FP-12".