A pointer in a class points to an other member function in the same class?

[James.D]

Hi, I met such a problem:

//---------------------
// .h
class CA
{
protected:
void (CA::*)m_pfn();

public:
CA();
void foo();

static void proc(CA *pObj); // NOTES it is a static member
};

//---------------------
// .cpp
CA::CA()
{
m_pfn = foo;
}

void CA::foo()
{
return;
}

void CA::proc(CA *pObj)
{
if (pObj->m_pfn)
(pObj->*m_pfn)(); // here I got two compile errors
}


I compiled my project in VS.net 2003, and in the line I marked, I got 2
errors: error C2597 and C2568
I don't know how to resolve this problem.

Any suggestions will be appreciated.

Thanks!


James

[John Carson]

Re: A pointer in a class points to an other member function in the same class?

"James.D" <ddddh@vip.sina .com> wrote in message
news:c27h0t$d76 $1@mail.cn99.co m[color=blue]
> Hi, I met such a problem:
>
> //---------------------
> // .h
> class CA
> {
> protected:
> void (CA::*)m_pfn();
>[/color]

Wrong syntax. It should be:

void (CA::*m_pfn)();
[color=blue]
> public:
> CA();
> void foo();
>
> static void proc(CA *pObj); // NOTES it is a static member
> };
>
> //---------------------
> // .cpp
> CA::CA()
> {
> m_pfn = foo;
> }
>
> void CA::foo()
> {
> return;
> }
>
> void CA::proc(CA *pObj)
> {
> if (pObj->m_pfn)
> (pObj->*m_pfn)(); // here I got two compile errors
> }[/color]

Also wrong syntax. It should be

(pObj->*pObj->m_pfn)();

This syntax performs two functions.

1. The first thing you need to do is retrieve the function pointer. The
pObj->m_pfn on the RIGHT returns the pointer value. Call it function_ptr for
short, so we end up with

(pObj->*function_ptr) ();

2. The second thing to do is to actually call the member function using the
function pointer. The remainder of the expression does just that. As with
all (non-static) member functions, you need to call the function by
binding it to an object.

To summarise, the object that pObj points to is needed twice: once as the
object storing the function pointer value, and once as the object that you
use to call the function (in this second capacity the object supplies a
"this" pointer so that the member function can access other members if
needed).


--
John Carson
1. To reply to email address, remove donald
2. Don't reply to email address (post here instead)

[John Carson]

Re: A pointer in a class points to an other member function in the same class?

I see that I have just wasted my time since you posted this question in two
other newsgroups and received an answer there. It is precisely for this
reason that multi-posting such as this is regarded as a breach of newsgroup
etiquette.


--
John Carson
1. To reply to email address, remove donald
2. Don't reply to email address (post here instead)

[Rolf Magnus]

Re: A pointer in a class points to an other member function in the same class?

James.D wrote:
[color=blue]
> Hi, I met such a problem:
>
> //---------------------
> // .h
> class CA
> {
> protected:
> void (CA::*)m_pfn();
>
> public:
> CA();
> void foo();
>
> static void proc(CA *pObj); // NOTES it is a static member
> };
>
> //---------------------
> // .cpp
> CA::CA()
> {
> m_pfn = foo;
> }
>
> void CA::foo()
> {
> return;
> }
>
> void CA::proc(CA *pObj)
> {
> if (pObj->m_pfn)
> (pObj->*m_pfn)(); // here I got two compile errors
> }
>
>
> I compiled my project in VS.net 2003, and in the line I marked, I got
> 2 errors: error C2597 and C2568
> I don't know how to resolve this problem.[/color]

And I don't know what error "C2597" and "C2568" are. Could you please
add the text of those messages? Not everyone has a Microsoft compiler
installed.

[David Harmon]

Re: A pointer in a class points to an other member function in the same class?

On Thu, 4 Mar 2004 23:12:26 +0800 in comp.lang.c++, "James.D"
<ddddh@vip.sina .com> was alleged to have written:[color=blue]
> (pObj->*m_pfn)(); // here I got two compile errors[/color]
[color=blue]
>I compiled my project in VS.net 2003, and in the line I marked, I got 2
>errors: error C2597 and C2568[/color]

There should be some explanatory text associated with the error reports.
Read the text and consider what it says. It's near impossible to
determine the nature of a compile error without reading the message.

[James.D]

Re: A pointer in a class points to an other member function in the same class?

I am so sorry about that.

Because the comiler I used is a Chinese version, so the text associated with
the error number is in Chinese.
I can't translate it into English prefectly.

:(


James


"David Harmon" <source@netcom. com> дÈëÓʼþ
news:408d550e.2 60629703@news.w est.earthlink.n et...[color=blue]
> On Thu, 4 Mar 2004 23:12:26 +0800 in comp.lang.c++, "James.D"
> <ddddh@vip.sina .com> was alleged to have written:[color=green]
> > (pObj->*m_pfn)(); // here I got two compile errors[/color]
>[color=green]
> >I compiled my project in VS.net 2003, and in the line I marked, I got 2
> >errors: error C2597 and C2568[/color]
>
> There should be some explanatory text associated with the error reports.
> Read the text and consider what it says. It's near impossible to
> determine the nature of a compile error without reading the message.
>[/color]

[James.D]

Re: A pointer in a class points to an other member function in the same class?

Sorry, I it is almost the first time I asking in newsgroup.

I really don't know the etiqette.
And I will notice this in the next time.

Thank you very much for your answer and your advice.


James


"John Carson" <donaldquixote@ datafast.net.au > дÈëÓʼþ
news:40475461@u senet.per.parad ox.net.au...[color=blue]
> I see that I have just wasted my time since you posted this question in[/color]
two[color=blue]
> other newsgroups and received an answer there. It is precisely for this
> reason that multi-posting such as this is regarded as a breach of[/color]
newsgroup[color=blue]
> etiquette.
>
>
> --
> John Carson
> 1. To reply to email address, remove donald
> 2. Don't reply to email address (post here instead)
>[/color]