Re: derive class - C / C++ / MFC Discussion Boards

Cedric Moonen10-Oct-06 4:49

10-Oct-06 4:49

baerten wrote:
But in an instance, the function is precised and accessible, so why does the fctpointer
don't save the "linkage"

Because with a member function, there is an explicit parameter that is passed to your function: the this parameter (pointer to the instance of the class). If you post some code, maybe we can help you. Basically, what you need to do is specify that the functions in your list are members of your class (by addind a CMyClass:: in front). But without seeing code, it is difficult.

Cédric Moonen
Software developer

Charting control [Updated - v1.1]

Re: Function Pointer

baerten10-Oct-06 5:05

baerten

10-Oct-06 5:05

void RTB::Config_Customer()<br />
{<br />
  // Creates X Elements in the Internal List<br />
  InternList = (BasicRow**)malloc(NumberofRows*sizeof(BasicRow*));<br />
  for(int i=0; i<NumberofRows; i++)<br />
    InternList [i] = new CustomerRow(); // Instance of a specialized Row<br />
<br />
  ActFillRow = InternList[0];  // Initialised on the first entry<br />
<br />
  CustomerRow* ActCustomerToFill = static_cast<CustomerRow*>( ActFillRow ); // ActFillRow is a BasicRow-pointer <br />
  // Creates the 8 Meta-Data Elements<br />
  MetaTable= (MetaInfo*)malloc(8*sizeof( MetaInfo));<br />
  MetaTable[0].Name = "Name";<br />
  MetaTable[0].Func = &CustomerRow::SetName; // The pointer to the function that Sets the Name to the column "Name"<br />
  MetaTable[1].Name = "Firstname";<br />
  MetaTable[1].Func = &CustomerRow::SetFirstname;<br />
    <br />
}

The MetaTable :

typedef struct MetaInfoForColumns {<br />
  CString Name;<br />
  ColumnSetter Func;<br />
} MetaInfo;

Column Setter:

typedef void (CustomerRow::*ColumnSetter)(CString); // Functionspointer

Thanks a lot

Re: Function Pointer

Mark Salsbery10-Oct-06 6:22

Mark Salsbery

10-Oct-06 6:22

You're going to need a CustomerRow object to make the call to MetaTable[].Func if the function is a non-static member variable. If you make the columnsetter functions static they are going to
need a CustomerRow object to access any non-static CustomerRow members.
You could pass a CustomerRow reference/pointer to the function
that uses the metatable to dispatch to the corresponding column setter function.
Without seeing how you are using the metatable I can't give you a code example Smile | :)

Mark

Re: Function Pointer

Anonymuos10-Oct-06 5:22

Anonymuos

10-Oct-06 5:22

baerten wrote:
I like to create a functionpointer on an instance of an object.

Try: http://www.parashift.com/c++-faq-lite/pointers-to-members.html[^]

Changing the drive name in a tree control

kiranin10-Oct-06 3:45

kiranin

10-Oct-06 3:45

When i displaying all the drives in the tree control,
it displayes drive names as A, C, D like that now i want to this drives as with required names

Re: Changing the drive name in a tree control

David Crow10-Oct-06 3:56

David Crow

10-Oct-06 3:56

Don't confuse drive letter (i.e., name) with volume name.

"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

"Judge not by the eye but by the heart." - Native American Proverb

derive class

Max++10-Oct-06 3:28

Max++

10-Oct-06 3:28

I derive CStr from CString as..

class CStr : public CString
{
public:
CStr();
virtual ~CStr();
};

and then I declare object of CStr and call some function from CString

void CTestDialogDlg::OnOK()
{
CStr obj;

obj.GetLength();
obj = "Test";
}

the first line is OK but the second line complier show error.
It because I can't call operator in parent class, Right ?
If so, How I define string to object.

Re: derive class

David Crow10-Oct-06 3:31

David Crow

10-Oct-06 3:31

Max++ wrote:
I derive CStr from CString as...

Are you sure this is what you want, since CString has no virtual destructor?

Max++ wrote:
...but the second line complier show error.

Are we supposed to guess the error? It likely has to do with a missing "using" declaration.

Aside from the dtor issue, the only argument I can see in your case for going ahead with the derivation is that you want to give your class a new ctor. Because ctors aren't inherited, you must be prepared to write forwarding ctors for all the CString ctors you want to be available in your derived class. Also, if you care about the return types of assignment operators, you must writing forwarding assignment operators. Compared to writing a handful of non-member "free" functions, this begins to sound like a lot of pointless work.

"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

"Judge not by the eye but by the heart." - Native American Proverb

Re: derive class

Stephen Hewitt10-Oct-06 13:42

Stephen Hewitt

10-Oct-06 13:42

DavidCrow wrote:
Are you sure this is what you want, since CString has no virtual destructor?

This is only an issue if you're going to delete it polymorphically.

Steve

[Message Deleted]

toxcct10-Oct-06 3:47

toxcct

10-Oct-06 3:47

[Message Deleted]

Re: derive class

David Crow10-Oct-06 3:54

David Crow

10-Oct-06 3:54

toxcct wrote:
you don't add it any functionnality

I'm fairly certain he had plans on adding a few extra methods. Trimming code snippets down to the bare minimum is quite common.

"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

"Judge not by the eye but by the heart." - Native American Proverb

Re: derive class

Stephen Hewitt10-Oct-06 13:46

Stephen Hewitt

10-Oct-06 13:46

toxcct wrote:
you'll have to redefine all the operators that are not declared virtual in the CString class

No you wont. They'll be inherited.

Steve

Re: derive class

led mike11-Oct-06 4:53

led mike

11-Oct-06 4:53

Stephen Hewitt wrote:
No you wont. They'll be inherited.

Yes but you won't have a const CStr& operator=(LPCTSTR); so ...

CStr t;
t = _T("hello world");

will not compile.

led mike

Re: derive class

Zac Howland10-Oct-06 4:15

Zac Howland

10-Oct-06 4:15

CString doesn't have a virtual destructor, so you need to be very careful about this.

Also, since Microsoft used poor design with CString, many of the operators are member functions, which means the left hand side of the operator cannot be implicitly casted to a CString object. You can call the parent operator, but the syntax is not very pretty. I would recommend not deriving from CString and simply creating methods to operate on one (depending on what you are trying to do).

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

sizeof(float)/sizeof(float[0])

Alex Cutovoi10-Oct-06 3:05

Alex Cutovoi

10-Oct-06 3:05

Hi fellows

I have a single question. I have a float array that have 6 elements all of them initialized with values. I need to find out the size of this array. Let's called my float array of theArray. I use this commom formula: sizeof(theArray)/sizeof(theArray[0]).
My results are strange, because it returns 1. I use this code to see the values:

<br />
char cTemp[50];<br />
   sprintf(cTemp, "%d %d %d", sizeof(dVertexes), sizeof(dVertexes[0]), sizeof(dVertexes)/sizeof(dVertexes[0]));<br />
   MessageBox(NULL, cTemp, "", MB_OK);<br />

In the first and in the second values it returns "4", and in the third value it returns "1".
Why it returns 1? Did this operation returns the correct size of array(in my case "6")?

thanks for the support

Re: sizeof(float)/sizeof(float[0])

C^hris L^osinger10-Oct-06 3:10

C^hris L^osinger

10-Oct-06 3:10

Alex Cutovoi wrote:
Why it returns 1?

4/4 = 1

4 = size of a pointer

is dVertexes allocated dynamically ? if so, you can't use that sizeof trick to get its size.

-c

image processing | blogging

Re: sizeof(float)/sizeof(float[0])

Alex Cutovoi10-Oct-06 3:30

Alex Cutovoi

10-Oct-06 3:30

my array is declared as following:

<br />
float fVertexes[6];<br />

I'm inserting this values;

<br />
fVertexes[0] =  1.0;<br />
fVertexes[1] =  0.0;<br />
fVertexes[2] = -1.0;<br />
fVertexes[3] =  1.0;<br />
fVertexes[4] = -1.0;<br />
fVertexes[5] = -1.0;<br />

I'm passing this guy to a function, like this:

<br />
primitive.Shape(GL_TRIANGLES, fVertexes, 1,1,1);<br />

Again, why it returns 1 if I don't create this guy dynamically?

Re: sizeof(float)/sizeof(float[0])

James R. Twine10-Oct-06 3:32

James R. Twine

10-Oct-06 3:32

   That is an example of the decay I mentioned in my post - when you pass the array, it becomes a pointer in the called function.

   The function that has the pointer has no "internal" or automatic way of knowing how much the data points to. That is why whenever you pass an array of data to a function, you usually have to tell the function how much valid data is in the array (or have a special element in the array to indicate the end of valid data).

   Peace!

-=- James

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Re: sizeof(float)/sizeof(float[0])

Galatei10-Oct-06 3:41

Galatei

10-Oct-06 3:41

Hi,

Just modify Shape function by adding INT nCount after pointer to array of floats. Then in Shape function, calculate array size as nCount*sizeof(float). nCount should specify the size of the array.

Regards

Re: sizeof(float)/sizeof(float[0])

Alex Cutovoi10-Oct-06 3:57

Alex Cutovoi

10-Oct-06 3:57

I made this:

I've passed the size of the array(like you've said) and divided by float[0] and works fine

Re: sizeof(float)/sizeof(float[0])

Alex Cutovoi10-Oct-06 4:01

Alex Cutovoi

10-Oct-06 4:01

I made some modifications and works fine. Thanks for the support

Re: sizeof(float)/sizeof(float[0])

James R. Twine10-Oct-06 3:14

James R. Twine

10-Oct-06 3:14

   The math is working: 4/4=1.

   The problem looks like dVertexes is not a true array. It is an atomic type (double) or a pointer.

   Note that using sizeof(...) in this way does not work correctly with pointers to arrays, even if they are pointers that have decayed from a true array.

   Peace!

-=- James

Re: sizeof(float)/sizeof(float[0])

Alex Cutovoi10-Oct-06 3:35

Alex Cutovoi

10-Oct-06 3:35

ok, so how can I discover the array size? I don't want to use vectors....

Re: sizeof(float)/sizeof(float[0])

James R. Twine10-Oct-06 3:36

James R. Twine

10-Oct-06 3:36

You have to pass the size to the called function to let it know how much valid data exists.

Peace!

-=- James

Re: sizeof(float)/sizeof(float[0])

Alex Cutovoi10-Oct-06 3:59

Alex Cutovoi

10-Oct-06 3:59

I've made this:
primitive.Shape(GL_TRIANGLES, fVertexes, sizeof(fVertexes), 0,1,1);

And in the function I'm divided the size of array by the size of first element in the array. Works fine, thanks for help

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