ATL / WTL / STL

Re: for_each / accumulate

5-Apr-03 10:03

is there a way to do this:

// get a sum of the results from calling a single member function on each element
int sum = 0;
for (myIterator it = sv.begin(); it != sv.end(); it++)
{
  sum+=(*it).GetValue();
}

using for_each or accumulate, without writing extra functions? in other words, i want it all on one line...

// something like...
int sum = std::accumulate(sv.begin(), sv.end(), 0, some_way_to_call_GetValue()_on_the_current_item);

?

(i should really go buy an STL book)

-c

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valikac6-Apr-03 6:47

valikac

6-Apr-03 6:47

No.

Kuphryn

Re: for_each / accumulate

Zdeslav Vojkovic7-Apr-03 23:36

Zdeslav Vojkovic

7-Apr-03 23:36

not exactly without extra functions, but you will need + operator. here's something similar:

class CLong
{
public:
CLong(long l) : m_val(l){;}
const long Val() const {return m_val;}

CLong operator+(const CLong& rhs)
{
return CLong(m_val + rhs.Val());
}
private:
long m_val;
};

using namespace std;

int main(int argc, char* argv[])
{
std::vector<CLong> v;
v.push_back(1L);
v.push_back(4L);
v.push_back(9L);

CLong csum(0);

csum = accumulate( v.begin(), v.end(), csum, mem_fun1_ref(&CLong::operator+));

cout << "sum: " << csum.Val();
return 0;
}

Re: for_each / accumulate

jbarton10-Apr-03 2:34

jbarton

10-Apr-03 2:34

There is a way to do this by writing a template for the functor. You can do something like:

<br />
#include <iostream><br />
#include <numeric><br />
#include <vector><br />
<br />
using namespace std;<br />
<br />
template<typename SumType, class D><br />
class MemFuncAdder<br />
{<br />
public:<br />
   typedef SumType (D::*func) () const;<br />
<br />
   MemFuncAdder( func f )<br />
      {<br />
      m_f = f;<br />
      }<br />
<br />
   SumType operator() (SumType running_sum, const D& data)<br />
      {<br />
      return (running_sum + (data.*m_f) () );<br />
      }<br />
private:<br />
   func  m_f;<br />
};<br />
<br />
class Data<br />
{<br />
   int value1;<br />
   int value2;<br />
   public:<br />
      Data( int v1, int v2) : value1(v1), value2(v2) {}<br />
<br />
      int  V1() const { return (value1); }<br />
      int  V2() const { return (value2); }<br />
<br />
      friend ostream& operator<< ( ostream &os, const Data &data)<br />
      {<br />
         os << "( " << data.value1 << ", " << data.value2 << ")";<br />
         return os;<br />
      }<br />
};<br />
<br />
int main(int argc, char* argv[])<br />
{<br />
   vector<Data>  array;<br />
<br />
   array.push_back( Data( 1,1) );<br />
   array.push_back( Data( 1,2) );<br />
   array.push_back( Data( 1,3) );<br />
   array.push_back( Data( 1,4) );<br />
   array.push_back( Data( 1,5) );<br />
<br />
   copy( array.begin(), array.end(), ostream_iterator<Data>( cout, ", " ));<br />
   cout << endl;<br />
<br />
   cout << "Result 1 = " << accumulate( array.begin(), array.end(), 0, MemFuncAdder<int,Data>(&Data::V1) ) << endl;<br />
   cout << "Result 2 = " << accumulate( array.begin(), array.end(), 0, MemFuncAdder<int,Data>(&Data::V2) ) << endl;<br />
<br />
   return 0;<br />
}<br />

Once you provide the MemFuncAdder template, you can call accumulate on multiple member functions without needing to write additional code. If you need a different operation other than addition, you could provide other templated functor classes.

CListCtrl as STL container

C^hris L^osinger4-Apr-03 4:04

4-Apr-03 4:04

has anyone ever seen a wrapper for a list control or tree control that can act as an STL container?

i'm dealing with a CListCtrl right now, and i noticed that it would be great to be able to do something like:

foreach(m_listCtrl.begin(), m_listCtrl.end(), do_something_with_selected_items);

or, to load items:

m_listCtrl.insert(lvitem);
m_listCtrl.push_back(lvitem);

you could treat a list control as a vector. and you could treat a CTreeCtrl as a tree (duh) of some kind. maybe you could sort the list control with std::sort, etc..

i don't need this functionality, i just thought it would be a really slick bit of code.

-c

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Joaquín M López Muñoz4-Apr-03 4:14

Joaquín M López Muñoz

4-Apr-03 4:14

It would be a nice contribution (volunteers? Smile | :)

). Anyway, I think this should be modelled after std::list rather than std::vector.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

C^hris L^osinger4-Apr-03 4:25

4-Apr-03 4:25

if i knew anything about the internals of an STL container, i would've written it myself before giving away the idea. maybe i'll take a look at your map for inspiration Smile | :)

-c

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Nick Parker4-Apr-03 4:38

Nick Parker

4-Apr-03 4:38

Chris Losinger wrote:
has anyone ever seen a wrapper for a list control or tree control that can act as an STL container?

How about this:

WINSTL[^].

-Nick Parker

C^hris L^osinger4-Apr-03 4:52

4-Apr-03 4:52

yup, that's pretty close.

-c

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Custom property pages for device manager using WTL

Neville Franks12-Apr-03 12:13

Neville Franks

12-Apr-03 12:13

Another way to look at this is to turn it on its head and say use a virtual list box which accessed items directly in the STL vector etc.

There are many advantages to this approach. eg. No parallel copies of the data to maintain and keep in sync, faster population of the control as it doesn't need to copy the data, more efficient memory use etc.

I've written a tree control that works like this. It uses an abstract container class to request the items it needs to display, and has absolutely no knowledge of where the data elements live or what they are. You can see this in the ClassView, Ascii Chart and Skeleton trees in ED.

Neville Franks, Author of ED for Windows. www.getsoft.com
Make money with our new Affilate program

NarayanaRajaniX3-Apr-03 17:31

NarayanaRajaniX

3-Apr-03 17:31

NEw custom property pages should be added to the device manager's property sheet using WTL. I used CPropertyPageImpl<> base class for this. Property page is not being displayed. IF new tab in the devicemanager prperties dialog box is clicked application is crashing.

Rajani

How to create Transparent Bitmap?

jkav3-Apr-03 16:43

jkav

3-Apr-03 16:43

Hi there,

I am working on CStatic control of VC++. I want to load Bitmap on the CStatic control with Transparent Background. For that I have created the Object of CBitmap. But It seems that CBitmap is not having transparent property. Can anybody show me the way, how to make CBitmap object transparent? I am creating Bitmap with CretateBitmap() method and after that I am Loading Bitmap to the CBitmap Object with LoadBitmap() method. These are the basic steps required to load Bitmap to the newly created Bitmap, but I don't know how to make it Transparent? Is there anybody who knows the trick? Please, show me the way...

Thanx in Advance,

Regards,
Kav
India

Re: How to create Transparent Bitmap?

Ed Gadziemski7-Apr-03 4:56

Ed Gadziemski

7-Apr-03 4:56

See my program http://www.codeproject.com/wtl/smasher.asp which has a transparent bitmap class.

using cin.getline() with string

Luis E. Cuadrado3-Apr-03 2:47

Luis E. Cuadrado

3-Apr-03 2:47

Hello everybody:
I was wondering if ther is a way to use the cin.getline() function when you use string objects. With the code snipet below I get the following error:

error C2664: 'class std::basic_istream<char,struct std::char_traits<char> > &__thiscall std::basic_istream<char,struct std::char_traits<char> >::getline(char *,int,char)' : cann
ot convert parameter 1 from 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >' to 'char *'
        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
Error executing cl.exe.

hwproject.exe - 1 error(s), 0 warning(s)

I always encounter this problem and I don't know what to do to solve this. Is there a better way to do this with string objects? Can you tell me what I did wrong with the code below? Any answer is more than welcome.

#include <string><br />
#include <iostream><br />
using namespace std;<br />
<br />
void main()<br />
{<br />
        int itemNum;<br />
        string Desc;<br />
        cout << "Enter Item Number: ";<br />
        cin >> itemNum;<br />
        cout << "Enter Description: ";<br />
	cin.getline(Desc, sizeof(Desc), (char)"\n");<br />
}

Luis E. Cuadrado
Blush | :O

)

valikac3-Apr-03 13:31

valikac

3-Apr-03 13:31

One solution is std::getline().

string sInput;
std::getline(cin, sInput);

Kuphryn

Luis E. Cuadrado4-Apr-03 1:55

Luis E. Cuadrado

4-Apr-03 1:55

Thanks for replying Kuphryn. I gave it a try and the program complies but when I run it, the variable where I store the value using the std::getline() function doesn't show up when I use cout.

#include <iostream>
#include <string>
using namespace std;
 
void main()
{
string itemID;
string Desc;
cout << "Enter ID: ";
cin >> itemID;
cout << "Enter Description: ";
getline(cin, Desc);

cout << "itemID: " << itemID << endl;
cout << "Desc: " << Desck << endl;

}

This is the output that I got.

Enter ID: 222
Enter Description: matches
itemID: 222
Desc:

I'm asuming that there are some kind of garbage collecting thing that I have to do here, is it? Let me know what you think.

Thanks for your help,

Luis E.

Luis E. Cuadrado
Blush | :O

)

Joaquín M López Muñoz4-Apr-03 2:33

Joaquín M López Muñoz

4-Apr-03 2:33

Hola Luis,

There are two problems, one of them is not your fault:

std::getline is broken in MSVC++ 6.0. See here[^] for a fix.

(this assumes you've installed the previous fix) After reading the int, there are extra characters pending to be read in the first line (at least, the terminating '\n'): eat this before going for the description:

#include <iostream>
#include <string>
 
using namespace std;
void main()
{
  string itemID;
  string Desc;
  cout << "Enter ID: ";
  cin>>itemID;
  cout << "Enter Description: ";
  getline(cin, Desc); // eats what remains of the previous line
  getline(cin, Desc);
  cout << "itemID: " << itemID << endl;
  cout << "Desc: " << Desc << endl;
}

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo