serious: GCC 2.95.3 accepts illegal function call

[Zack Weinberg]

On Fri, Sep 07, 2001 at 08:27:34PM +0200, Michael Noisternig wrote:
> Check this:
> 
> --- begin code ---
> 
> typedef long long uint64;
> 
> uint64 calculate_cpu_timing_factors (unsigned int instr)
> {
> 	// ...
> }
> 
> uint64 calculate_cpu_timing()
> {
> 	return calculate_cpu_timing(calculate_cpu_timing(10000)/1024);
> }
> 
> --- end code ---
> 
> This piece of code is happily accepted by the compiler! Check it 'til
> you find the error, it took me the whole day :-(((

Would you believe this is completely valid, if dubious, ANSI C?

The prototype you put on the definition of the second function,

uint64 calculate_cpu_timing() { ... }

does _not_ mean "this function takes no arguments."  It means "This
function may be called with any argument list whatsoever."  You may be
used to C++, where that prototype _does_ mean "this function takes no
arguments."

If you had written instead

uint64 calculate_cpu_timing(void) { ... }

the compiler would have diagnosed the error you expected it to:

test.c: In function `calculate_cpu_timing':
test.c:10: too many arguments to function `calculate_cpu_timing'
test.c:10: too many arguments to function `calculate_cpu_timing'

I believe this is allowed in C++ too.

[You may wonder why on earth the standard allows such a bizarre thing;
it is for compatibility with pre-standard C, in which there were no
function prototypes.]

zw