Short code to determine compiler's

[andre]

In article <225800197 at uxe.cso.uiuc.edu> mcdonald at uxe.cso.uiuc.edu writes:
>
>>Some students here had to determine the number of registers (data 
>>and address, we use 680x0's) the C compiler uses.  A friend and
>>I wrote the following code to show to some students having trouble.
>>It is very short and simple, but it seems to work.  The only logical
>>next step is to post it to comp.lang.c and have it torn apart!

[ text explaining why this doesn't always work ]

>In fact, the really interesting question is, in legal C, is it
>even POSSIBLE to write a program to see how many registers are used?

Yes, I think you can write a program that checks the nr of registers,
but you will get the answer at compile time, not run time :-)

the program looks like this:

/* test register usage of compiler */

main()
{
	register n1, n2, n3, n4, n5, n6, n7, n8; /* etc. */
	int *a;

	a = &n8;
	a = &n7;

	/* repeat n6 - n2 */
	a = &n1;
}

/* end */

The compiler will assing n1 to n{x} to the registers it has available and
the rest will be normal variables. You can take the address of a variable
but not of a register, so the compiler will start to complain at the first
line that tries to take the address of a register. That's why the a = &n{x};
lines must count backwards.

	I would like to know if this is also possible at run-time,
		Andre

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