Sizes of stack variables

Hey All,
I was just trying to minimize the size of a program the other day,
and I noticed that the size of the varibles created on the stack is not necessarily the size they should be. So, for instance, the following code:

void main()
{
char buffer[8];

printf("%s\n", buffer);
}

produces the following assembly:
...
8 main:

9    pushl %ebp
10   movl  %esp, %ebp
11   subl  $24, %esp
12   andl  $-16, %esp
13   movl  $0, %eax
     ...

No problem right, the buffer variable is created on the stack, and I am assuming that the number 24 being subtracted from the stack pointer is the 8 bytes for the buffer + 16 bytes program overhead(environment, etc). Now, if I change the source to the following:

void main()
{
char buffer[16];

printf("%s\n", buffer);
}

produces the following assembly:
...
8 main:

   9    pushl %ebp
   10   movl  %esp, %ebp
   11   subl  $40, %esp
   12   andl  $-16, %esp
   13   movl  $0, %eax

...

Shouldn't the stack size only increase to 32 which is 16 bytes of overhead plus the 16 bytes for the variable?

If someone has some insight into this I would be much abliged.

Chuck

Hi the stack size depends on the optimization of the compiler ( gcc ) .Just read the stack frame that is used from the compiler.You can find such info in http://gcc.gnu.org or sth similar.

Best regards,
Chris.