Because it exposes a completely implementation detail to the public interface, (unnecessarily at that) So yes it is for philosophical reasons that we must reject this badly designed C standard.
Barry On Aug 17, 2011, at 2:58 PM, Matthew Knepley wrote: > On Wed, Aug 17, 2011 at 9:08 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > On Aug 17, 2011, at 2:04 PM, Chetan Jhurani wrote: > > >> From: Jed Brown > >> Sent: Wednesday, August 17, 2011 12:38 PM > >> To: For users of the development version of PETSc > >> Subject: Re: [petsc-dev] declaring argument as const basic type in PETSc > >> > >> On Wed, Aug 17, 2011 at 11:34, Barry Smith <bsmith at mcs.anl.gov> wrote: > >>> But my question remains, should we const declare function arguments? > >> > >> No, the prototype should never use const for stack arguments (pointer to > >> const > >> is totally different and should be used anywhere that it is correct). > >> > >> I don't know any responsible libraries that const-ify value parameters in > >> prototypes. I think it most commonly arises from ignorance of, or > >> sloppiness > >> with, the actual semantics of the C language. > > > > > So by the standard a compiler should never bitch if in the function > definition it is declared const but in the extern prototype it is not > declared const? (This is an exception to the usual rule that the extern > arguments should match the definition arguments?) > > Just so I understand, this declaration and definition: > > void foo(const int a); > > void foo(const int a) { > } > > is legal, and would prevent a developer from accidentally assigning to a, but > we are outlawing it. I do not > see the rationale. > > Matt > > Thanks > > Barry > > > It is useful to have const pass-by-value parameters in function > > definitions. Not useful in the function declarations or for the > > caller. > > > > This is so that a developer does not assign to a passed-in int > > unintentionally. Almost all C and C++ compilers accept it and they > > error out if one does something like the code below. An exception > > is old IRIX compilers that emit a warning on using const pass-by-value > > and said it is meaningless to use them. I disagree. > > > > void f(const int n, int* j) > > { > > *j = n; > > n = 0; // error > > } > > > > Of course it is more useful for preventing bugs in more complex > > functions. > > > > Chetan > > > > > > > > > -- > What most experimenters take for granted before they begin their experiments > is infinitely more interesting than any results to which their experiments > lead. > -- Norbert Wiener