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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
{
}
};
...
vector<CMyClass> v1;
vector<CMyClass> v2;
v1.push_back(CMyClass(1234));
v2.push_back(CMyClass(1234));
if (v1 == v2)
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
{
}
};
...
vector<CMyClass*> v1;
vector<CMyClass*> v2;
v1.push_back(new CMyClass(1234));
v2.push_back(new CMyClass(1234));
if (v1 == v2)
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!
The Rob Blog
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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>()))
Using a function object template means I can compare containers containing other pointer type - the EqualT operator() handles the de-referencing. Nice.
The Rob Blog
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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()))
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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'
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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);
bool IsEqual2 = (MyListOfA_PtrsX == MyListOfA_PtrsZ);
<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
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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.
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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++)
{
...
}
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(...);
v.push_back(...);
}
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?
The Rob Blog
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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 
LINKS~! Ericahist | 1ClickPicGrabber | CP SearchBar v2.0.2 | C++ Forum FAQ
Strange things are afoot at the U+004B U+20DD
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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...
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Looks like the Boost 'list_of' function is exactly what I need!
e.g.:
static const vector<int> v = list_of(1)(2)(3)
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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!
The Rob Blog
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You're right - it does work - I was having a blonde moment!
The STL rocks. I feel I have hardly scratched the surface yet already I am in awe of its capabilities...
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Don't forget to make operator() of your functors a const method. Otherwise it may not work, if your STL implementation passes the functor objects by const reference.
Good music: In my rosary[^]
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Top tip - cheers. It does actually mention this in the excellent C++ Standard Library book I have (Nicolai Josuttis) so there's no excuse...
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Greetings...
I have been working on some ATL controls which have MFC support. I can view the property page of the ATL classes and see the events they can handle, which are a partial list of those available to pure MFC classes. However I need to handle the event WM_SETTINGCHANGE and that is not listed as a possible event. I can manually type it under:
<br />
BEGIN_MSG_MAP(CSomeClass)<br />
...<br />
MESSAGE_HANDLER(WM_SETTINGCHANGE, OnSettingChange)<br />
...<br />
END_MSG_MAP()<br />
but this doesn't work..the debugger never stops in the OnSettingChange function.
However, if I make a new purely MFC project, WM_SETTINGCHANGE is listed under the events tap of the classe's property page, and it all works just fine.
The question I guess is, how can it be that ATL "with MFC support" has only some of the events? also what is the work arround, especially as in pure MFC the event handling function is in the form of
<br />
OnSettingChange(UINT uFlags, LPCTSTR lpszSection)<br />
and in ATL control project with MFC support it is in the form of:
<br />
OnSettingChange(UINT , WPARAM , LPARAM , BOOL& )<br />
Thanks,
Aristotel 
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Hi,
In my main frame I have a splitter pane with two views. I want to scroll the appropriate window when the mouse hovers over it. What is the best way to do this?
I was thinking of handling the WM_MOUSEWHEEL message and checking if the cursor is within the bounds of the view's rectangle (using GetCursorPos() and GetWindowRect()) but I think it would waste too many CPU cycles
Is there a better way?
Thanks in advance.
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First, this is not the appropriate forum: you'll get more response in the Visual C++ forum as it is purely related to visual C++ and MFC.
For your question, do you know that if you make your views inherits from CScrollView instead of CView, this is automatically managed ? You'll have also scroll bars at the bottom and at the right of your views.
Hope this helps
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cedric moonen wrote:
as it is purely related to visual C++ and MFC
How do you figure? He never mentions MFC, so I think we should assume that he's using WTL.
--
An eye for an eye will only make the world blind.
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Sorry, I don't know WTL and the words mainframe and splitter made me believe he was using the MFC.
Next time, I'll ask before saying something wrong 
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The MSDN docs says:
The WM_MOUSEWHEEL message is sent to the focus window when the mouse wheel is rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message, since DefWindowProc propagates it up the parent chain until it finds a window that processes it.
After having read that, my first stab at the problem would be to process the WM_MOUSEWHEEL message at the splitter level. There I'd use WindowFromPoint() and GetCursorPos() to figure out which window it's over. Then I'd use GetParent() until I get either left or right pane window. Then I'd send the appropriate WM_xSCROLL messages to the correct pane.
--
An eye for an eye will only make the world blind.
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Hi, All!
When i trying to add a new ATL object to my project i see this error! May be smbd solve it?
Thanx!
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AdyOS wrote:
When i trying to add a new ATL object to my project i see this error
which error ?
AdyOS wrote:
May be smbd solve it?
certainly not, how could we ? we don't have neither the code nor any explanation of what you do nor the error message...
please understand us too if you want us to give some help...
TOXCCT >>> GEII power
[toxcct][VisualCalc]
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OK! I have an ATL project with support MFC. The project already have some ATL objects (there are Dilaogs). And now i try to add a new Dialog to my project, but when i click Insert->New ATL object i see this error. Before all was ok.
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