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Derived class ids
#define ID_DER1 01
#define ID_DER2 02
in base class, add a pure virtual function
virtual int GetTypeId() = 0;
its implementation in derived classes
int DerivedClass1::GetTypeId()
{ return ID_DER1; }
int DerivedClass2::GetTypeId()
{ return ID_DER2; }
and the foo function looks like
void foo(BaseClass* p)
{
switch (p->GetTypeID())
{
case ID_DER1: printf("der1");
break;
case ID_DER2: printf("der2");
break;
}
}
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As far as I know, it's not possible.
However, your code doesn't seems very nice: you are really breaking some basic principle of OOP. Why do you need to access the specific types ? Can't you instead use virtual functions and let each type implements the expected behavior as needed ?
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I use this to pass notification messages for progress updates, task finished, etc. from worker threads. I use it instead of callbacks. Some messages need their own userdata (hence derived classes, which contain the userdata). I could use callbacks with void* pParam for the userdata, and an ID to show the type of message (like PostMessage does), but RTTI already gives me the ID. The receiver of the message is not always derived from CWnd (otherwise I would have just used PostMessage instead of this whole thing).
There is sufficient light for those who desire to see, and there is sufficient darkness for those of a contrary disposition.
Blaise Pascal
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I still don't really understand what you need to do differently for the different types  . If these are some kind of "typed" messages, can't you just provide a virtual getText method that is overriden by each type ?
I really don't understand your scenario: what are those objects and why do you need to handle them differently based on their types ?
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Quick Question: What does switching on a type mean... especially if you're dynamically casting the result?
Answer: It means you're missing a virtual function!
So don't mess about with switches and casting, add a virtual function to the base class. This will give you three benefits:
- SPEEEEED - a virtual function call will always as fast or faster than a switch on a type_id
- It makes your code a lot easier to read. Your switch/if/then else is replaced by 1 line, yep
- It makes your code a lot easier to extend. If/when you add a new derived class you just have to implement the derived class, you don't have to mess about with the client code.
SO... Just say no to switching on type_id. You know it makes sense.
Cheers,
Ash
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Couldn't agree more 
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Hi all,
i m using a button and create its variable from CBitmapButton derived class,
and load bitamps on this button CBitmapButton::LoadBitmaps function.
but when i focus the button and press enter key here the button is not pressed while its working for space key.
please help me for this.
thanks in advance.
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This if I remember correctly is exactly how it should behave. On a Dialog pressing enter will 'click' the dialog's default button, otherwise you will need to handle WM_KEYUP and trap VK_ENTER
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Hi all,
I want to add a combobox in a List control
when clicking a column in the list control
How to do this?
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See here.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
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Hi!
I've decalred a pointer variable inside a class. I'm assigning value to this variable inside a function. I've to make this variable visible to classes in other files. How to make this visible to other files?
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it depends on the relationship between the two classes. However an instance or pointer to an instance of the first class is required to access its members from another classes. So keep a pointer to the first class in other classes from which you want to access the variable. Or declare the variable as 'public static' so that it canbe be accessed from anywhere by using ClasssName::variable syntax.
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If you really want to do this (and judging by other questions you've posted on these forums I'm waiting for the inevitable "my pointer's being overwritten/when I dererference the pointer an exception is thrown" question) then:
- add a member function to the class that returns the pointer
- include the header with the class in it to the other files that contain code that you want to mangle^h^h^h^h^h^haccess the pointer.
Generally (although not always) it's a bad idea to expose a class's internally dangly bits to the outside world like this though. If you start thinking of classes less as dumping grounds for data but as things that do stuff your question changes from: "How do I access this pointer?" to "what behaviour do I want my class to have?" You'll probably find that you only need a small subset of what unfettered pointer access gives you in the code you currently think of as wanting access and your code will be a bit safer as a result.
Cheers,
Ash
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{
DWORD dw;
int i;
char ch;
printf("Enter first value=");
scanf("%x",&dw);
printf("\nEnter second value=");
scanf("%d",&i);
printf("\nEnter single character=");
//control not stop here......
scanf("%c",&ch);
}
Here program control does not stop at
"scanf("%c",&ch);"
Waiting 4 reply.
Thanks
Sagar
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So what values have you entered for the two integers before the scanf for the character? If you entered "Fred" at the first prompt then no conversion will happen and there'll still be characters left in the buffer for the final call.
To get around this check the return value of scanf to make sure that you're actually reading and converting something. If it's zero read everything you can and try and try again.
And I've just noticed that you're reading a DWORD using %x. Even if it doesn't fail you want to be reading values through this format specifier into an int.
Cheers,
Ash
PS: The final call to scanf, does it leave a newline character in ch? I can't remember how scanf processes newlines but it might be an avenue to investgate.
Edited to correct my Unglish.
modified on Wednesday, July 28, 2010 4:28 AM
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By "Enter Key" control goes to next line.
And in ch value of last "Enter key" pressed was coming.
The solution for my problem is, need to flush the standrad input stream using fflush(stdin).
Thank you for response.
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After every scanf statement put the statement fflush(stdin).
This clears the keyboard buffer of any leftover characters.
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Can any one give tips in how to use pdb file. Currently i am working in real time project. Where we give only the executable to customer. Rare occasion the appilication crashes. Is analysing pdb is good procedure. If so how to generate pdb for release version VC++. What settings has to be made set . If any give me simple example it much helpful for me.Thanks in advance.......
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Open the properties window of your project and select the release configuration, then:
- in the general section of C++ properties, ensure that the field Debug Information Format is set to Program Database (/Zi)
- in the debugging section of Linker properties, ensure that the field Generate Debug Info is set to Yes (/DEBUG) (the field Generate Program Database File will hold the path of the generated pdb file)
Cheers,
Sauro
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If you ship release binaries to the customer your code will be optimised and therefore using the pdb file will make no sense. In the past I've logged a callstack to a file when an unhandled exception has occurred by setting a hook into the kernel exception handler the walking the stack. Doing this can give you a stack in hex (though functions are often missing due to optimisation). You can then decode the stack information using a map and cod files generated at build time giving you the line in the code that caused the exception.
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BOOL checkExistence(HKEY *hKey, LPCTSTR lpszAppName)
{
CRegKey regKey;
if( regKey.Open(HKEY_LOCAL_MACHINE, _T("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Uninstall"),
KEY_READ) != ERROR_SUCCESS )
return FALSE;
DWORD dwIndex = 0;
DWORD cbName = 128;
TCHAR szSubkeyName[128];
CString strSubkeyName;
int nHasAllItems = 0;
while( regKey.EnumKey(dwIndex, szSubkeyName, &cbName) != ERROR_NO_MORE_ITEMS )
{
dwIndex++;
cbName = 128;
strSubkeyName.Format(_T("%s"), szSubkeyName);
if( strSubkeyName.Compare(lpszAppName) )
{
nHasAllItems++;
continue;
}
else
break;
}
regKey.Close();
if( nHasAllItems == dwIndex )
return FALSE;
else
{
*hKey = regKey.m_hKey;
return TRUE;
}
}
I wrote this funx to check whether there's a particular installed app in the registry. After calling this funx, hKey is expected to be assigned the registry handle. But prob occurs as Ive indicated above.
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