C / C++ / MFC

11-Jul-06 19:28

I'm trying a double indirect look-up table for some function pointer in my app (yep, I have good reason).
I'm trying to use std::map for the table but (because of the double indirection) I need to use a "std::map*"
Which I don't know how to map[index] (with a pointer)

Now perhaps I'm misusing it, I'm not sure (I know nothing of STL and I have some problem understanding its header)

Anyway here is my code (problem explained in red), if you could give me some tips.....

static std::map<const char*, SEL> map_sels;
static std::map<OClass, std::map<SEL, IMP>*> map_imps;

void id::GetImpAlways(const char* name, SEL& sel, IMP& imp)
{
    if( !_handle )
        throw gcnew ObjectDisposedException(Class()->Name);

    if(map_sels.find(name) == map_sels.end())
    {
        sel = sel_register_name(name);
        map_sels[name] = sel;
    }
    else
    {
        sel = map_sels[name];
    }

    std::map<SEL, IMP> * class_imps; <font color="red">// here I get the problematic "map *"</font>
    if(map_imps.find(_handle->class_pointer) == map_imps.end())
    {
        class_imps = new std::map<SEL, IMP>();
        map_imps[_handle->class_pointer] = class_imps;
    }
    else
    {
        class_imps = map_imps[_handle->class_pointer];
    }

    if(class_imps->find(sel) == class_imps->end())
    {
        imp = get_imp(_handle->class_pointer, sel);
        if( !imp )
            throw gcnew ObjectiveCException("No such method");
        class_imps[sel] = imp;  <font color="red">// can't do that with 'map*', what should I so?</font>
    }
    else
    {
        imp = class_imps[sel]; <font color="red">// can't do that with 'map*', what should I so?</font>
    }
}
<pre>

Re: Problem with STL [modified]

Steve Echols11-Jul-06 19:40

Steve Echols

11-Jul-06 19:40

Have you tried dereferencing the pointer like:

*class_imps[sel] = imp;<br />
<br />
and <br />
<br />
imp = *class_imps[sel];

- S
50 cups of coffee and you know it's on!

Super Lloyd11-Jul-06 19:50

11-Jul-06 19:50

I am afraid it will create a copy or affect a copy.
I need to alter the static global variable!!

I hate this stupid C++ copy policy, I need to affect the real shared object!!

Steve Echols11-Jul-06 20:48

Steve Echols

11-Jul-06 20:48

Yeah, I agree. I use pointers for storing my objects in containers (right or wrong), just because I know (or think I know) there's only one instance of my object lying around.

I think these classes are good for simple intrinsic types, like ints, etc., but get kind of irritating when you have to define copy, less than and assignment operators for your classes. Just my opinion, of course.....

- S
50 cups of coffee and you know it's on!

Super Lloyd11-Jul-06 19:50

Re: Problem with STL [modified]

11-Jul-06 19:50

BTW, never mind my problem.
The program crash at the first line:
if(map_sels.find(name) == map_sels.end())

How do I do?
I have a home made C hashtable possibly I should use it instead :-/

Super Lloyd11-Jul-06 20:14

Re: Problem with STL [modified]

11-Jul-06 20:14

Never mind STL...
I can't even add an element, it throws exception like:

at std._Tree<std::_Tmap_traits<void *,void *,std::less<void *>,std::allocator<std::pair<void * const,void *> >,0> >._Lbound(_Tree<std::_Tmap_traits<void \*\,void \*\,std::less<void \*>\,std::allocator<std::pair<void \* const\,void \*> <\,0> >* , Void** _Keyval)

at std.map<void *,void *,std::less<void *>,std::allocator<std::pair<void * const,void *> > >.[](map<void \*\,void \*\,std::less<void \*>\,std::allocator<std::pair<void \* const\,void \*> > >* , Void** _Keyval)

And what is it supposed to mean?
I just try to run this simple code:

static std::map<void*, void*> map_sels;
map_sels[(void*)name] = (void*)sel;

I dropped it, I will use my C Hashtable.
At least it is simple to use, make no copy and no fuss!... Mad | :mad:

-- modified at 2:17 Wednesday 12th July, 2006

Stephen Hewitt11-Jul-06 20:55

11-Jul-06 20:55

Your problem has nothing to do with maps: it's a simple pointer error. Here's the relevant bits of your code:

std::map<SEL, IMP> * class_imps; // here I get the problematic "map *"
// ...
class_imps[sel] = imp;  // can't do that with 'map*', what should I so?
// ...

class_imps is a pointer but you're using it as if it was a map. This should look like this:

(*class_imps)[sel] = imp;

Here's an example to make this clearer:

class Foo
{
    void Bar();
};
 
void SomeFunction()
{
    Foo *pFoo = new Foo();
    pFoo.Bar(); // Error. Should be pFoo->Bar() or (*pFoo).Bar().
    delete pFoo;
}

Steve

-- modified at 3:01 Wednesday 12th July, 2006

PS: Use typedefs instead or repeating the long map types all over the place.

Super Lloyd11-Jul-06 21:02

11-Jul-06 21:02

I knew I was calling the operator on an invalid object.

But I don't want to use "plain object" (as opposed to pointer).
if I do that, as far as I know, I will work with copy of the object, not the real object.

And I don't care about the life of the copies!

Anyway I dropped STL and used my own C implementation of hashtable.
No copy, no fuss... Poke tongue | ;-P

Stephen Hewitt11-Jul-06 21:15

11-Jul-06 21:15

I didn't suggest you not use a pointer. I suggested you don't confuse the pointer with what it points to. You done this:

class_imps[sel] = imp;

I suggested you do this:

(*class_imps)[sel] = imp;

In the first you're not even using the map, you're using a pointer to a map. In the second you're using the map and the only thing copied is imp when the map makes a copy to store. Given that the map's mapped type is IMP this is exactly right.

Steve

Super Lloyd11-Jul-06 21:39

11-Jul-06 21:39

You misunderstood what I said. I said the same thing as you!

That's understandable, as I probably confused you is when I implyed that (*class_imps) was making a copy.
Of course it doesn't, silly me!
Poke tongue | ;-P

Too late I am using my C Hashtable now.
It works well and there is absolutely no copy whatsover (whereas std::map use some sort of default allocator as far as I know).

beside I was not able to use it at all!

example:
std::map<void*, void*> map;
map[(void*)1] = (void*) 2;

is throwing some mysterious (and C++) looking exception.

Stephen Hewitt11-Jul-06 21:50

11-Jul-06 21:50

Super Lloyd wrote:
It works well and there is absolutely no copy whatsover

You're wrong there. If it stores pointers then the pointers are copied; same as with a map of pointers. If it stores IMPs then the IMP must be copied; again the same as a map of IMPs.

I tried your code and it works fine. Here's what I tested:

#include <map>
#include <iostream>
 
int main(int argc, char *argv[])
{
    using namespace std;
 
    typedef map<void*, void*> VoidStar2VoidStarMap;
 
    VoidStar2VoidStarMap MyMap;
    MyMap[reinterpret_cast<void*>(0)] = reinterpret_cast<void*>(1);
 
    cout << MyMap[reinterpret_cast<void*>(0)] << endl;
 
    return 0;
}

The reinterpret_cast<void*> is the same as the (void*) cast in your code. I make it a rule never to use C-style casts.

You're using managed C++ aren't you? I use unmanaged C++ - I don't approve of managed C++.

Steve

Super Lloyd11-Jul-06 22:11

11-Jul-06 22:11

Stephen Hewitt wrote:
You're wrong there. If it stores pointers then the pointers are copied; same as with a map of pointers. If it stores IMPs then the IMP must be copied; again the same as a map of IMPs.

Hum.. you're right....

Stephen Hewitt wrote:
I tried your code and it works fine.

does it?

Stephen Hewitt wrote:
You're using managed C++ aren't you? I use unmanaged C++ - I don't approve of managed C++.

I confess that I'm not that at ease with native C++.
I jumped from C to C#/Managed C++ (well I did some ObjectiveC & Java too)

But everytime I should do pure C++ brrr....
Not too mention that code that did compile in 1995 no longer compiled in 1998! (yes this way! not the opposite!)
And that GCC and CL don't support the same set of C++ D'Oh! | :doh:

Beside many tests failed to prove to me that C++ perform that much faster, so why bother Poke tongue | ;-P

Stephen Hewitt11-Jul-06 22:26

C2664 error.......in evc++4.0

11-Jul-06 22:26

Super Lloyd wrote:
Beside many tests failed to prove to me that C++ perform that much faster, so why bother

I've found it hard to find any benchmarks that I can trust. If I was going to use dotNET I'd use C#. The main problems I have with dotNET is firstly memory consumption and secondly the speed. Many dotNET supporters concede that the memory consumption is high but say RAM is cheap. I don't buy this argument: as a developer I have many, many applications open at the same time - If they all consume heaps of memory then the computer will start paging sooner and the whole system suffers.

Steve

cool_frozen11-Jul-06 17:54

cool_frozen

11-Jul-06 17:54

hi frnds,

this error come due to parameter conversion failures.... but i hav tried for the best....
anybody having some better n easy solution...

line that is having error in my code....

DWORD dw=nthol(i_net(Ip.Getbuffer(MAX_PATH)))

Ip is a CString class.....

Re: C2664 error.......in evc++4.0 [modified]

bob1697211-Jul-06 18:46

bob16972

11-Jul-06 18:46

Just a wild guess here,

Is inet_addr what your looking for?

bob1697217-Jul-06 19:56

bob16972

17-Jul-06 19:56

Well, for starters, your missing a closing parenthesis.

secondly, no need to use CString::GetBuffer() when you are needing a const char* since CString already has an operator for that. Only use CString::GetBuffer() when you need a buffer to pass into something. It won't hurt you here except you forgot the corresponding ReleaseBuffer() but that's a different story.

Thirdly, C++ is case sensitive so that call to strIP.Getbuffer() won't get you anything except another error to add to the list. strIP.GetBuffer() is probably what you meant.

Fourth, I took your code and fixed the above statements, included the #include "winsock2.h"

and made reference to ws2_32.lib and I was able to compile it and run it so I'm not sure what your fighting...

CString strIP="192.168.1.1";
DWORD dw=ntohl(inet_addr(strIP));
TRACE("Big Endian dw = %u\n",dw);

Any additional data in the time since your last post?

-- modified at 1:57 Tuesday 18th July, 2006

cool_frozen17-Jul-06 23:39

cool_frozen

17-Jul-06 23:39

thanks for the help bob....
i will see whether ur code will help or not....but im sure it will help...thanks again......
regards..
frozen

led mike11-Jul-06 19:25

led mike

11-Jul-06 19:25

what is i_net() function?

what is nthol() function is it supposed to be ntohl()? Which takes a u_long parameter so why would you be getting it from a CString object? I cannot understand what you are trying to do.

"Just about every question you've asked over the last 3-4 days has been "urgent". Perhaps a little planning would be helpful?"
Colin Angus Mackay in the C# forum

led mike

cool_frozen12-Jul-06 20:48

cool_frozen

12-Jul-06 20:48

YEAH U R RIGHT....

I MISTYPED THE CODE....

CODE IS...
DWORD dw=ntohl(inet_addr(strIP.GetBuffer(MAX_PATH)));
strIP IS A CString class...

error message i m getting is...

C2664: inet_addr()..can not convert parameter 1 from "unsigned long *" to "const char *"

i m using eVC++4.0