ATL / WTL / STL

16-Dec-05 5:19

Hi!

I'm a newbie and trying the <list>.

I want to save the objects of this class into a list.

<br />
#ifndef HEADER<br />
#define HEADER<br />
<br />
class MyClass<br />
{<br />
      private:<br />
        char m_myVar1  [255];                      <br />
        char m_myVar2  [255];       <br />
        <br />
      public:	    <br />
        MyClass();<br />
        ~MyClass();   <br />
        const char* getMyVar1() { return m_myVar1; }<br />
        const char* getMyVar2() { return m_myVar2; }<br />
};<br />
<br />
#endif<br />

Could anyone help me with some snips? Many thanks!

toxcct18-Dec-05 21:14

18-Dec-05 21:14

first, you create a list of the type you want to store in it :

#include <LIST>
#include "MyClass.h"
 
std::list<MyClass> myList;

then, you use it as a list of any other types... :

MyClass o1();
MyClass o2();
myList.add(o1);
myList.add(o2);

see what i mean ?

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

-- modified at 5:14 Thursday 22nd December, 2005

Re: stl use &lt;list&gt;

nne-vitamin21-Dec-05 22:15

21-Dec-05 22:15

Thank you very much, it works!

Now I have another problem. How can I sort the list? myList.sort() doesn't work! I found some codes but they don't work properly. I don't know how to write correctly. My intention is to sort the list on m_myVar1 or m_myVar2. I would like to write a method that has these possibilities.

Do you know what I mean?

-- modified at 4:17 Thursday 22nd December, 2005

toxcct21-Dec-05 22:25

Re: stl use &amp;amp;amp;amp;amp;amp;amp;lt;list&amp;amp;amp;amp;amp;amp;amp;gt;

21-Dec-05 22:25

you have to write your own comparator (because list::sort() doesn't know how to sort your objects type) and then, pass it to sort(). this is a bit weird for newbies, i conceed.

the other way to do it (and maybe the easiest) is to add a comparison operator in your class to allow sort() to sort your objects.

for example :

<font color=blue>class</font> MyClass {
  <font color=blue>private</font>:
    <font color=blue>char</font> m_myVar1[255]; 
    <font color=blue>char</font> m_myVar2[255]; 
 
  <font color=blue>public</font>: 
    MyClass();
    ~MyClass(); 
    <font color=blue>const char</font>* getMyVar1();
    <font color=blue>const char</font>* getMyVar2();
 
    <font color=green>// these are for comparison</font>
    <font color=blue>bool operator</font> <  (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> >  (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> <= (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> >= (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> == (<font color=blue>const</font> MyClass&);
};

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

-- modified at 5:13 Thursday 22nd December, 2005

nne-vitamin21-Dec-05 23:10

21-Dec-05 23:10

Thank you!

But I don't know how to pass it to sort().

I write my code so:

class MyClass {
  private:
    char m_myVar1[255]; 
    char m_myVar2[255]; 
 
  public: 
    MyClass();
    ~MyClass(); 
    const char* getMyVar1() { return m_myVar1; }
    const char* getMyVar2() { return m_myVar2; }
 
    // these are for comparison
    bool operator <  (const MyClass&);
    bool operator >  (const MyClass&);
    bool operator <= (const MyClass&);
    bool operator >= (const MyClass&);
    bool operator == (const MyClass&);
};

-----------


#include <LIST>
#include "MyClass.h"
int main()
{ 
  std::list<MyClass> myList;
  MyClass o1;
  MyClass o2;
  myList.push_back(o1);
  myList.push_back(o2);
  myList.sort(); // don't how to pass it to sort & sort based on m_myVar1 or m_myVar2 
  return 0;
}

-- modified at 5:18 Thursday 22nd December, 2005

toxcct21-Dec-05 23:13

21-Dec-05 23:13

you don't pass it, sort will use them !!!
it is mentioned on the link on the msdn site i provided previously that sort() (without parameter) will sort in the ascending order...

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

-- modified at 5:13 Thursday 22nd December, 2005

Re: stl use &lt;list&gt;

nne-vitamin21-Dec-05 23:31

21-Dec-05 23:31

I got compiler faults: "... public: bool __thiscall MyClass::operator<(class MyClass const &)" (??MCID3@@QAE_NABV0@@Z ...."

Do I have to define these methods anywhere????

// these are for comparison
bool operator < (const MyClass&);
bool operator > (const MyClass&);
bool operator <= (const MyClass&);
bool operator >= (const MyClass&);
bool operator == (const MyClass&);

Isn't it only the prototypes????

toxcct21-Dec-05 23:59

Re: stl use &amp;amp;amp;amp;amp;amp;amp;lt;list&amp;amp;amp;amp;amp;amp;amp;gt;

21-Dec-05 23:59

nne-vitamin wrote:
Do I have to define these methods anywhere????

yes of course !!
in general, we declare a class in a .h file, and implement it in a .cpp.

myclass.h:
<font color=blue>class</font> MyClass {
  <font color=blue>private</font>:
    <font color=blue>char</font> m_myVar1[255]; 
    <font color=blue>char</font> m_myVar2[255]; 
 
  <font color=blue>public</font>: 
    MyClass();
    ~MyClass(); 
    <font color=blue>const char</font>* getMyVar1();
    <font color=blue>const char</font>* getMyVar2();
 
    <font color=green>// these are for comparison</font>
    <font color=blue>bool operator</font> <  (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> >  (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> <= (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> >= (<font color=blue>const</font> MyClass&);
    <font color=blue>bool operator</font> == (<font color=blue>const</font> MyClass&);
};

myclass.cpp:
MyClass::MyClass() {
    <font color=green>//initialise your class instance here...</font>
}
 
MyClass::~MyClass() {
    <font color=green>//free memory allocated on the heap here...</font>
}
 
<font color=blue>const char</font>* MyClass::getMyVar1() {
    <font color=blue>return this</font>->myVar1;
}
 
<font color=blue>const char</font>* MyClass::getMyVar2() {
    <font color=blue>return this</font>->myVar2;
}
 
<font color=blue>bool</font> MyClass::operator < (<font color=blue>const</font> MyClass& crefCl) {
    <font color=green>//do the comparison here...</font>
}
 
<font color=blue>bool</font> MyClass::operator > (<font color=blue>const</font> MyClass& crefCl) {
    <font color=green>//do the comparison here...</font>
}
 
<font color=blue>bool</font> MyClass::operator <= (<font color=blue>const</font> MyClass& crefCl) {
    <font color=green>//do the comparison here...</font>
}
 
<font color=blue>bool</font> MyClass::operator >= (<font color=blue>const</font> MyClass& crefCl) {
    <font color=green>//do the comparison here...</font>
}
 
<font color=blue>bool</font> MyClass::operator == (<font color=blue>const</font> MyClass& crefCl) {
    <font color=green>//do the comparison here...</font>
}

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

-- modified at 6:35 Thursday 22nd December, 2005

nne-vitamin22-Dec-05 0:38

22-Dec-05 0:38

Thank you very much! But I don't know what (the comparisons) I have to write to the definition of these classes operators?

bool MyClass::operator < (const MyClass& crefCl) { //do the comparison here...}
bool MyClass::operator > (const MyClass& crefCl) { //do the comparison here...}
bool MyClass::operator <= (const MyClass& crefCl) { //do the comparison here...}
bool MyClass::operator >= (const MyClass& crefCl) { //do the comparison here...}
bool MyClass::operator == (const MyClass& crefCl) { //do the comparison here...}

I only want my list to be sorted based on the content of m_myVar2. If the contents of m_myVar2 are:

"One"
"Two"
"Three"
"Four"

so after calling myList.sort() the contents should be alphabetically sorted like:

"Four"
"One"
"Three"
"Two"

How can I do that? If you write: //do the comparison here...
I cannot guess what.

-- modified at 6:44 Thursday 22nd December, 2005

toxcct22-Dec-05 0:47

22-Dec-05 0:47

damn !!! is it so hard ?! WTF | :WTF:

<font color=blue>#include</font> <string.h>
<font color=blue>bool</font> MyClass::operator < (<font color=blue>const</font> MyClass& crefCl) {
    <font color=blue>return</font> (::strcmp(m_myVar2, crefCl.GetVar2()) < 0);
}
 
<font color=blue>bool</font> MyClass::operator > (<font color=blue>const</font> MyClass& crefCl) {
    <font color=blue>return</font> (::strcmp(m_myVar2, crefCl.GetVar2()) > 0);
}
 
<font color=blue>bool</font> MyClass::operator <= (<font color=blue>const</font> MyClass& crefCl) {
    <font color=blue>return</font> (::strcmp(m_myVar2, crefCl.GetVar2()) <= 0);
}
 
<font color=blue>bool</font> MyClass::operator >= (<font color=blue>const</font> MyClass& crefCl) {
    <font color=blue>return</font> (::strcmp(m_myVar2, crefCl.GetVar2()) >= 0);
}
 
<font color=blue>bool</font> MyClass::operator == (<font color=blue>const</font> MyClass& crefCl) {
    <font color=blue>return</font> (::strcmp(m_myVar2, crefCl.GetVar2()) == 0);
}

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

-- modified at 6:47 Thursday 22nd December, 2005

Re: stl use &lt;list&gt;

nne-vitamin22-Dec-05 0:57

22-Dec-05 0:57

Thank you! The important secret of your hints came at last. So it was very hard! Even though thank you very much!

toxcct22-Dec-05 0:59

Re: stl use &amp;amp;lt;list&amp;amp;gt;

22-Dec-05 0:59

nne-vitamin wrote:
The important secret of your hints came at last

and the important question still remains... : does it work ?

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

nne-vitamin22-Dec-05 1:26

22-Dec-05 1:26

Sorry, no.

The compiler fault: 'getMyVar2' : this-pointer cannot be converted from 'const class MyClass' to 'class MyClass &'

If I write:

bool MyClass::operator < (const MyClass& crefCl) { return (::strcmp(m_myVar2, crefCl.m_myVar2) < 0);}

the same fault

toxcct22-Dec-05 2:11

Re: stl use &amp;amp;lt;list&amp;amp;gt;

22-Dec-05 2:11

sorry, i give up... learn C++ first... D'Oh! | :doh:

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

nne-vitamin22-Dec-05 2:44

Re: stl use &amp;amp;amp;lt;list&amp;amp;amp;gt;

22-Dec-05 2:44

Thank you! Yes I am a newbie! Therefor I ask. Why do you make it so difficult to me? It is your Intention?

It is so easy to post a simple code instead to make a secret from that.
I find out the easy way myself bei Codeguru, only short way:

http://www.codeguru.com/forum/showthread.php?t=366063[^]

toxcct22-Dec-05 2:51

Re: stl use &amp;amp;amp;lt;list&amp;amp;amp;gt;

22-Dec-05 2:51

nne-vitamin wrote:
Why do you make it so difficult to me?

2 things :
- because it is not difficult if you know the basics of C++ (which is apprently not the case)
- the example on codeguru is exactly what i suggested you, but unfortunately, you didn't apply it correctly. it's not my fault buddy. learning C++ was only a good advice, now, the balls are in your area ; you do what you want...

TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VisualCalc 3.0]

Axter25-Dec-05 1:06

Axter

25-Dec-05 1:06

FYI:
Most C++ experts recommend that you make operator<() a non-member function.
And that you create a operator<=() as a member function.

That paticular example in CodeGuru is not a good one, and it may be a little out date.

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

Refer MSDN code, but STL's operator () has problem!

simonchen.net14-Dec-05 18:30

simonchen.net

14-Dec-05 18:30

// We use this object so that list::sort() can sort in a different
// order.Normally greater<> is used. We override it here to switch to
// less.
class less_str : public greater<string> {
public:
bool operator()(const string& _X, const string& _Y) const
{
return _X <= _Y;
}
};

I have directly use the list.sort(less_str());
In this processing, I have trace into ...
but it always get into greater<string> operator (), why it don't get into less_str operator()?

Re: Refer MSDN code, but STL's operator () has problem!

toxcct15-Dec-05 0:41