ATL / WTL / STL

[newbie] subclass std::list?

8-Jul-05 18:49

Yeah, I did things the hard way in that example - there's no need to manually build the SINK_MAP macros since ClassWizard (in VC6 at least) can do it for you. I haven't looked at VC7 enough to know where the equivalent feature is but I would assume it's still in there.

--Mike--
Visual C++ MVP Cool | :cool:

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ehh8-Jul-05 4:08

ehh

8-Jul-05 4:08

hello,

i've created a std::list of objects, and it works well, but i'd like to support additional functionality for the list, such as writing certain aspects of the objects to stdout/cout (or dumping them using TRACE macros), matching certain aspects of objects (i.e., several different "match" functions), populating a list box with objects' names, etc. i've tried 2 approaches:

1. wrap the std::list in a class that handles these functions by using the list's iterators. this is inelegant, so i switched to:

2. subclass my std::list<myobject>, and add the functions i need to the new class. from what i've read on the web, subclassing std::list isn't a good idea, due to the virtual destructor problem.

my guess is that i should be using functions that operate on this list, but creating functions instead of list methods seems to violate the whole point of using c++. i'd appreciate any advice, since this is my first project using the stl, and i'm still waiting for my stl book to arrive in the mail....

ed

Re: [newbie] subclass std::list?

Stuart Dootson8-Jul-05 7:48

Stuart Dootson

8-Jul-05 7:48

If you don't add any new data in your derived class, you should be OK in most cases (because your derived destructor won't actually need to do anything more than the std::lsit destructor).

OTOH - ehh wrote: violate the whole point of using c++ - well, C++ is a multi-paradigm language, so using separate free functions doesn't really violate any point of C++....

Stuart Dootson

'Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p'

COPY question???

Melena7-Jul-05 6:49

Melena

7-Jul-05 6:49

Hi All,

I have a program which uses the IE engine to display HTML documents (using ATL) in my program's window. I'm trying to figure out how to make the COPY work, when some of the highlighted display is right-clicked.

The program isn't creating the edit menu which appears when it is right-clicked, so I assume IE is doing that. The COPY appears in the menu, but clicking on it does not copy the text to the clipboard (at least, doing paste after that does not paste what I just tried to copy). If I display the same html doc in Internet Explorer, then the copy works fine.

I've tried adding this code:

m_spOleCmdTarg->Exec(NULL,OLECMDID_COPY,OLECMDEXECOPT_DONTPROMPTUSER,NULL,NULL);

which does get executed when the user clicks on Copy in the System Menu. But still, the paste does not paste what I just tried to copy.

Does anyone have any idea what I might be missing here? Any ideas are greatly appreciated.

Thanks,

Melena Confused | :confused:

Michael Dunn8-Jul-05 18:53

8-Jul-05 18:53

I did this in one of my apps:

// pWB2 is a IWebBrowser2* on the WebBrowser control hosed in my app
pWB2->ExecWB ( OLECMDID_COPY, OLECMDEXECOPT_DONTPROMPTUSER, NULL, NULL );

and it works without a hitch. I'm using a different interface than you, however.

--Mike--
Visual C++ MVP Cool | :cool:

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Melena11-Jul-05 5:59

Melena

11-Jul-05 5:59

Thanks Mike.

So you didn't have to enable anything to make the copy work? I've seen things like UIEnable function calls, so I'm wondering if that's what I'm missing.

Also, had you created your own menu which is run when the user right-clicks in the browser, or was it just using the IE engine right-click menu? I'm wondering how you knew when to execute the pWB2->ExecWB...

Thanks again,

Melena

Melena13-Jul-05 5:39

Melena

13-Jul-05 5:39

I've figured this problem out. Was using CoInitialize() instead of OleInitialize(). The OleInitialize() makes the clipboard available, once I started using that, the copy worked fine.

Michael Dunn14-Jul-05 2:59

Comparing STL containers of pointers

14-Jul-05 2:59

cool

--Mike--
Visual C++ MVP Cool | :cool:

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Rob Caldecott7-Jul-05 5:24

7-Jul-05 5:24

If I have an STL container that contains objects, then I can compare them easily - for example:

class CMyClass
{
int m_n;
CMyClass(int n) : m_n(n) { }

bool operator==(const CMyClass& o) const
{
// User defined comparison operator here
}
};

...

vector<CMyClass> v1;
vector<CMyClass> v2;
v1.push_back(CMyClass(1234));
v2.push_back(CMyClass(1234));

if (v1 == v2) // Calls CMyClass operator==

However, I often use containers of pointers, and when I do, comparing two containers doesn't call the objects operator== function. For example:

class CMyClass
{
int m_n;
CMyClass(int n) : m_n(n) { }

bool operator==(const CMyClass& o) const
{
// User defined comparison operator here
}
};

...

vector<CMyClass*> v1;
vector<CMyClass*> v2;
v1.push_back(new CMyClass(1234));
v2.push_back(new CMyClass(1234));

if (v1 == v2) // Simply compares the value of each pointer, so not much use!

My question is - are there any operators I can overload to make the comparison work for containers of pointers, or do I need to hand-roll my own comparison function? I hope this makes sense!

Re: Comparing STL containers of pointers

Rob Caldecott7-Jul-05 6:07

7-Jul-05 6:07

OK, after some experimenting I realised that std::equal can be passed a function object, so I now have something like this:

template <class T>
class EqualT
{
public:
	inline bool operator()(const T* t1, const T* t2) { return *t1 == *t2; }
};

...

vector<CMyClass*> v1;
vector<CMyClass*> v2;
...

if (equal(v1.begin(), v1.end(), v2.begin(), EqualT<CMyClass>()))
// The containers are equal

Using a function object template means I can compare containers containing other pointer type - the EqualT operator() handles the de-referencing. Nice.

Ooops...

Rob Caldecott7-Jul-05 6:33

Re: Comparing STL containers of pointers

7-Jul-05 6:33

I meant:

struct EqualT
{
template <class T>
inline bool operator()(const T* t1, const T* t2) const { return *t1 == *t2; }
};
...
vector<CMyClass*> v1;
vector<CMyClass*> v2;
...
if (equal(v1.begin(), v1.end(), v2.begin(), EqualT()))
// Equal!

Ooops...

Jörgen Sigvardsson7-Jul-05 9:56

Jörgen Sigvardsson

7-Jul-05 9:56

The power of STL, you have seen! Smile | :)

Good music: In my rosary[^]

Stuart Dootson8-Jul-05 7:45

Stuart Dootson

8-Jul-05 7:45

You could use boost::indirect_iterator[^] - then you don't need to do anything much (except use Boost!).

Of course, you're pulling a fair number of headers in, but who knows, you might find other parts of Boost you want to use...

Stuart Dootson

'Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p'

Re: Comparing STL containers of pointers

Axter4-Aug-05 18:28

Axter

4-Aug-05 18:28

I recommend you use a smart pointer like the following:
http://code.axter.com/clone_ptr.h

The above smart pointer has operator==() functions that work on the object itself instead of the pointer.

Example code:

#include <iostream><br />
#include <list><br />
#include "clone_ptr.h"<br />
<br />
using namespace std;<br />
<br />
class A<br />
{<br />
public:<br />
	A(int a) : m_a(a) {}<br />
	virtual ~A() {}<br />
	virtual void Somefunction() const<br />
	{<br />
		cout << "I'm A " << m_a << endl;<br />
	}<br />
	bool operator==(const A& Src)const{return (m_a == Src.m_a);}<br />
	int m_a;<br />
};<br />
<br />
class B : public A<br />
{<br />
public:<br />
	B(int a) : A(a) {}<br />
	void Somefunction() const<br />
	{<br />
		cout << "I'm B " << m_a << endl;<br />
	}<br />
};<br />
<br />
class C : public A<br />
{<br />
public:<br />
	C(int a) : A(a) {}<br />
	void Somefunction() const<br />
	{<br />
		cout << "I'm C " << m_a << endl;<br />
	}<br />
};<br />
<br />
int main(int argc, char* argv[])<br />
{<br />
	list<clone_ptr<A> > MyListOfA_PtrsX;<br />
	MyListOfA_PtrsX.push_back(new A(1));<br />
	MyListOfA_PtrsX.push_back(new A(2));<br />
	MyListOfA_PtrsX.push_back(new A(3));<br />
	<br />
	list<clone_ptr<A> > MyListOfA_PtrsY;<br />
	MyListOfA_PtrsY.push_back(new B(4));<br />
	MyListOfA_PtrsY.push_back(new B(5));<br />
	MyListOfA_PtrsY.push_back(new B(6));<br />
	<br />
	list<clone_ptr<A> > MyListOfA_PtrsZ;<br />
	MyListOfA_PtrsZ.push_back(new C(1));<br />
	MyListOfA_PtrsZ.push_back(new C(2));<br />
	MyListOfA_PtrsZ.push_back(new C(3));<br />
<br />
	bool IsEqual1 = (MyListOfA_PtrsX == MyListOfA_PtrsY); //Should be false<br />
	bool IsEqual2 = (MyListOfA_PtrsX == MyListOfA_PtrsZ); //Should be true<br />
<br />
	cout << IsEqual1 << endl;<br />
	cout << IsEqual2 << endl;<br />
<br />
	system("pause");<br />
	return 0;<br />
}

Top ten member of C++ Expert Exchange.
http://www.experts-exchange.com/Cplusplus

dueto

Raudel6-Jul-05 5:49

Raudel

6-Jul-05 5:49

forgive me if my ask is not about the theme treated in this forum.
I am working in c++ builder 6.0, i am using the GetHeapStatus function to know the memory allocated by the application, but all the fields of the struct returned by the function are in 0, why can I do??
Thanks.

Initializing STL containers

Rob Caldecott6-Jul-05 5:22

6-Jul-05 5:22

I have a lot of places in my code where I am using a static const table that I then use for lookup purposes. For example:

static const struct
{
    LPCTSTR psz;
    UINT n;
} table[] =
{
    _T("Rob"), 1971,
    _T("Becky"), 1977,
};

...

for (int i = 0; i < sizeof(table) / sizeof(*table); i++)
{
    // Do something with a table element
    ...
}

This is all well and good, but now I am an STL fanatic I would rather using a static vector (so I can utilize find_if, for_each, etc.

My question - is there an elegant way to initialise a container whilst still making the whole thing const. For example, the following would be sweet:

class CMyData
{
public:
    LPCTSTR m_psz;
    UINT m_n;

    CMyData(LPCTSTR psz, UINT n) : m_psz(psz), m_n(n) { }
};

static const vector<CMyData> v =
{
    CMyData(_T("Rob"), 1971),
    CMyData(_T("Becky"), 1977),
};

The above doesn't work. No surprises. If instead I do something like this:

static const vector<CMyData> v;
if (v.empty())
{
    v.push_back(...); // ERROR
    v.push_back(...); // ERROR
}

The fact the vector is defined as 'const' means I can't add anything to it the first time the function is called. I guess I could instead do:

static vector<const CMyData> v;
if (v.empty())
{
    v.push_back(...);
    v.push_back(...);
}

The above works OK, but I wondered if any STL gurus had any other solutions?

Re: Initializing STL containers

Michael Dunn6-Jul-05 6:31

Re: Initializing STL containers

6-Jul-05 6:31

I don't see how making the container itself const would be useful. If you can't modify the vector, how can you add objects to it?
BTW check out boost::assign[^] for some neat classes that make STL container initialization nicer.

--Mike--
Visual C++ MVP Cool | :cool:

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Rob Caldecott6-Jul-05 6:39

Re: Initializing STL containers

6-Jul-05 6:39

Michael Dunn wrote:
I don't see how making the container itself const would be useful.

Because, like in my first static const struct example, I only want the container for lookups - I won't add anything to it once it has been initialized. Looks like I might have to check Boost out...

Rob Caldecott6-Jul-05 6:41

find_if and function objects ('functors')

6-Jul-05 6:41

Looks like the Boost 'list_of' function is exactly what I need!

e.g.:

static const vector<int> v = list_of(1)(2)(3)

Rob Caldecott5-Jul-05 3:11

5-Jul-05 3:11

Is there any way to use a function object with find_if instead of a predicate? Predicates have limited use, and it would be neat if I could do something like this:

struct findfunc
{
    CMyPtr* m_pData;
    findfunc(CMyPtr* p) : m_pData(p) { }
    bool operator()(CMyData* ptr)
    {
        return (ptr->blah == m_pData->blah);
    }
}

...

std::list<CMyData*> mylist;
...
CMyPtr somedata;
...
std::list<CMyData*>::iterator it = std::find_if(mylist.begin(), mylist.end(), findfunc(somedata));

Basically, I want to perform a more advanced search (on any STL container) than find_if currently allows. I am quite new to STL, so please bear with me!

Re: find_if and function objects ('functors')

Michael Dunn5-Jul-05 6:54

Re: find_if and function objects ('functors')

5-Jul-05 6:54

The code you posted should work fine. The functor trick lets you use an object (that defines operator() properly) in place of a function.

--Mike--
Visual C++ MVP Cool | :cool:

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Rob Caldecott5-Jul-05 22:48