C / C++ / MFC

7-Sep-04 8:05

I am working on a project where I need to track information for each row in a listctrl.

I have create a class for the tracking.

Then when I load the listctrl I create a new class and store the pointer in the SetItemData of the row.

Example:

SetItemData( GetItemCount() - 1 , ( DWORD ) new CTrackingObject() );

This works great. The problem I have: "How do I delete the class when the ListCtrl is destroyed.

I have tried overloading the DeleteAllItems() but when I call the GetItemCount() method, I get an error.

Any ideas of how I can call the pointers from the listctrl and delete the classes?

David Crow7-Sep-04 8:58

David Crow

7-Sep-04 8:58

Cedar Sith wrote:
SetItemData( GetItemCount() - 1 , ( DWORD ) new CTrackingObject() );

This is extremely unsafe code. The first parameter to SetItemData() should be the return value of InsertItem().

Cedar Sith wrote:
Any ideas of how I can call the pointers from the listctrl and delete the classes?

Whenever the window that owns the list contol is being destroyed, that is the correct time to delete each data item in the control.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Cedar Sith7-Sep-04 9:39

7-Sep-04 9:39

DavidCrow wrote:
Whenever the window that owns the list contol is being destroyed, that is the correct time to delete each data item in the control.

I assume you mean in the destructor of the listctrl.

I have this code but I still get errors.

for ( int i = 0 ; i < GetItemCount(); i++ ) {
delete ( CShippingObject* ) GetItemData( i );
}

GetItemCount throws an error.

Any new suggestions?

P.s. I have changed my code to be
int nNewId = InsertItem( ...);
SetItemData( nNewId , ( DWORD ) new CTrackingObject() );

David Crow7-Sep-04 9:54

David Crow

7-Sep-04 9:54

Cedar Sith wrote:
I assume you mean in the destructor of the listctrl.

No, I mean the owner of the list control. That's usually a dialog or a form view.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Cedar Sith7-Sep-04 10:33

7-Sep-04 10:33

DavidCrow wrote:
No, I mean the owner of the list control. That's usually a dialog or a form view.

I placed the following code in the form view destructor

for ( int i = 0 ; i < GetItemCount(); i++ ) {
delete ( CTrackingObject* ) GetItemData( i );
}

and received the same error.

It is almost as if once the parent window is closed the GetItemCount method no longer works.

Any new ideas? David, Thanks for the information so far.

Ryan Binns7-Sep-04 18:22

7-Sep-04 18:22

Cedar Sith wrote:
placed the following code in the form view destructor

That won't work. You have to do it before the list view is destroyed.

Cedar Sith wrote:
It is almost as if once the parent window is closed the GetItemCount method no longer works.

Of course it doesn't. None of the methods will work; because the list view has already been destroyed. You'll have to put the code in OnDestroy() at the very latest, before you call the base class OnDestroy() handler.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Cedar Sith8-Sep-04 9:24

8-Sep-04 9:24

Ryan Binns wrote:
OnDestroy()

OnDestroy was the key. Thank you.

I was able to call my overloaded DeleteAllItems that deleted all of the pointers from an overloaded OnDestroy in my Overloades CmyListCtrl Class.

Here are my methods:

BOOL CmyListCtrl::DeleteAllItems( )
{
if ( m_lpszType == "ShippingQuotes" ) {
for ( int i = 0 ; i < GetItemCount(); i++ ) {
delete ( CShippingObject* ) GetItemData( i );
}
}

return CListCtrl::DeleteAllItems();
}

void CmyListCtrl::OnDestroy()
{
DeleteAllItems();

CListCtrl::OnDestroy();
}

Thank you for everyone that helped me out.

Ryan Binns8-Sep-04 13:47

8-Sep-04 13:47

Cedar Sith wrote:
m_lpszType == "ShippingQuotes"

What type is m_lpszType? LPCTSTR? If so, this comparison almost definitely won't work. You can't compare two pointers as though they were strings. All it will check is that the pointers point to the same location. Even if they point to the same thing, if they are at different addresses, the comparison will be false. Use _tcscmp() instead.

Of course, if you're using CString this won't be a problem Smile | :)

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Cedar Sith8-Sep-04 14:15

8-Sep-04 14:15

Ryan Binns wrote:
m_lpszType == "ShippingQuotes"

m_lpszType is a CString. I use the overloaded CmyListCtrl in multiple places. Not every ListCtrl has pointers. So I use the type the differentiate the listctrls.

Cedar Sith7-Sep-04 12:25

STL / elegant file input (basic question!)

7-Sep-04 12:25

It seems that the MFC code for GetItemData and GetItemCount calls the following code:

ASSERT(::IsWindow(m_hWnd));

So if the window is being closed, mfc has already destroyed the m_hWnd pointer and mfc throws and error.

If anyone has an ideas on how to delete objects whose pointers have been placed in the itemdata field ... please let me know.

Thank you.

LiquidEyes7-Sep-04 8:03

7-Sep-04 8:03

At the moment I'm trying to make an effort to use std::string and std::ifstream in my work, instead of using "stdio.h". My main objective is to write elegant code -- performance is not an issue! Smile | :)

I need to read a lot of blocks (of various sizes) from file, and append them to various string buffers. The problem is that functions like ifstream::read are designed to read into char* style buffers, not strings; however there seems to be some kind of relationship between streambufs and strings that I figured might make my life easier...? Confused | :confused:

using namespace std;
...
string mystring;
ifstream inputfile;
int length = 20;

...

// is there a better way to do this...?
char* buffer = new char [length];
inputfile.read (buffer, length);
mystring += buffer;
delete[] buffer;

// this isn't much better...
char ch;
for (int i=0; i<length; i++)
{
    inputfile >> ch;
    mystring += ch;

    // presumably I could reserve extra space before the loop,
    // to avoid repeated resizing of the string...?
}

I have the gut feeling that there must be a really elegant way to do this, using some combination of streambuf / ifstream::operator>> / ifstream::read etc. I figured the whole point of using std::string was that it can worry about the allocation side of things behind the scenes. However I'm finding the documentation a little cryptic and generalised. Unsure | :~

Any ideas?

It's quite possible I just want the moon on a stick and I should go back to BASIC... Smile | :)

Ryan Binns7-Sep-04 18:32

7-Sep-04 18:32

LiquidEyes wrote:
Any ideas?

getline(inputfile, mystring); will read a string from a file. You can pass a third parameter (a character) that specifies a delimiter to use during the reading if you need to. By default, it stops after a newline character.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

LiquidEyes7-Sep-04 23:03

7-Sep-04 23:03

Thanks for the reply. However I don't see how it will know to stop after (say) 20 characters? Without a delimeter, will it read the whole file into the string?

I want to do the STL equivalent of

fread( mystring, sizeof(char), length, inputfile );

or failing that, use something more elegant than a char[] (which I have to allocate myself) as an intermediate buffer.

Kevin McFarlane8-Sep-04 2:14

Kevin McFarlane

8-Sep-04 2:14

From memory I think you can do getline(infile, mystring, "\n") or something.

Kevin

LiquidEyes8-Sep-04 2:21

8-Sep-04 2:21

I don't want it to stop on 'newline'. I want it to read a fixed number of bytes. Confused | :confused:

Kevin McFarlane8-Sep-04 6:43

Kevin McFarlane

8-Sep-04 6:43

I couldn't find that getline with no. of bytes that Ray mentioned. I suppose you could use the getline that gets the whole line and then use a substring function. Not as elegant but still avoids char*.

Kevin

Ryan Binns8-Sep-04 3:55

8-Sep-04 3:55

LiquidEyes wrote:
However I don't see how it will know to stop after (say) 20 characters?

It doesn't. You'll have to use the read() method of ifstream to do that.

LiquidEyes wrote:
Without a delimeter, will it read the whole file into the string?

No, as I said, the default delimiter is a newline - it will read a single line.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

LiquidEyes8-Sep-04 4:10

8-Sep-04 4:10

You'll have to use the read() method of ifstream to do that.

Precisely. Which takes us back to my original question ... what structure can I read into instead of an old fashioned char* array?

I just thought there might be an elegant way, using vectors or strings or something, that didn't involve allocating chars manually. As I said, maybe I just want the moon on a stick. Smile | :)

Ryan Binns8-Sep-04 4:28