massimo morara wrote:
> On Mon, May 21, 2007 at 10:00:03AM -0700, Rush Manbert wrote:
>
>>massimo morara wrote:
>>
>>> In the function xmlCopyNode(const xmlNodePtr node, int
>>>extended) [tree.c], what is supposed be 'const'?
>>>
>
>
>>Write the declaration out, then read it backwards to determine what is
>>const. In this case, I believe the declaration would be "const xmlNode
>>*", so reading it backward says that it's a pointer to a xmlNode that is
>>const. A const pointer would be "xmlNodePtr const node"
>
>
> Sorry, but i'm pretty sure that "const xmlNodePtr node" is (in
> "tree.h") "xmlNode * const node", so is the pointer that is costant;
> next i transcribe a little trivial program to verify a similar case.
> My question is: what we wish costant: the pointer or the data?
> If we wish that is costant the structure pointed, we should
> write "xmlNode const * node" or, defining in "tree.h" something like
>
> typedef xmlNode const * xmlConstNodePtr;
>
> write "xmlConstNodePtr node".
> For xmlCopyNode() and for other functions.
>
> massimo morara
>
>
> ps: sorry for my bad english
>
>
> ---- test program ----
>
>
> #include <stdio.h>
>
> typedef struct
> {
> int foo;
> } fooStruct ;
>
>
> typedef fooStruct * fooStrPtr;
>
>
> void changeFooData (const fooStrPtr pfd)
> {
> pfd->foo = 2;
>
> /* pfd++; forbidden */
> }
>
>
> int main (void)
> {
> fooStruct fooData;
>
> fooData.foo = 1;
>
> changeFooData(&fooData);
>
> printf("foo val: %i\n", fooData.foo);
>
> return(0);
> }
Massimo,
Sorry, my mistake. I thought that "const xmlNodePtr node" meant the same
thing as "const xmlNode * node", as if xmlNodePtr were a macro
definition that expanded to "xmlNode *", but the typedef changes things,
so the const modifies the pointer itself.
I took your example and changed changeFooData to this:
void changeFooData (const fooStruct * pfd)
{
pfd->foo = 2; /* <--- Forbidden */
pfd++;
}
and the compiler complains about the assignment, but not the increment,
so now it makes sense to me.
You are correct and I have learned something. The declaration means that
the pointer is const, not the data. If what you are asking for is the
intent, then Daniel will need to answer.
- Rush
_______________________________________________
xml mailing list, project page http://xmlsoft.org/
[email protected]
http://mail.gnome.org/mailman/listinfo/xml
