Re: Loops (was Re: do { quit; } else { })

On 12/05/2025 11:23, Keith Thompson wrote:

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

James Kuyper <jameskuyper@alumni.caltech.edu> writes:
[...]

It's main potential usefulness is not in the definition of the
function, but in calls to the function.  If the calls occur in
a different translation unit from the definition, the compiler
does not have the needed information.

>
It does if the visible declaration has the same information.

>
Like 'restrict', parameter array length information, specified by
way of 'static', is ignored outside of function definitions.  As
was intended (with 'restrict' also).

>
I think that by "is ignored", you mean that compilers are not
required to pay attention to it.  [...]

>
I mean it has no effect on program semantics.

 It affects whether a program has defined or undefined behavior.
(Yes, a conforming compiler could ignore it.)
 

The UB is actually at the function call site, rather than in the function itself.  Thus adding a "static N" to the function definition can change the semantics of the call site:
// file1.c
extern int foo(int * p);
int bar(void) {
int xs[4];
return foo(xs);
}
// file2.c
#define N 4
int foo(int p[static N]) {
return 42;
}
Changing "N" to 5 will render the call in file1.c undefined behaviour, without having any semantic effect on the function definition in file2.c