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In OO programming I think in terms of "is a" and "has a". "is a" means it IS a class while
"has a" refers to something that should be a member of a class.
While your method will work, it does't necessarily make sense.
To make it more clear, I'll give your classes appropriate names:
class ValidHexStringChecker;
class StringToHexConverter;
Class MyClass : public ValidHexStringChecker, public StringToHexConverter
{
};
ValidHexStringChecker and StringToHexConverter are base classes.
MyClass is a derived class, derived from both base classes.
MyClass IS A ValidHexStringChecker and it also IS A StringToHexConverter.
Unless MyClass encapsulates a string, it doesn't make sense for it to be a converter and checker.
It could HAVE ("has a") methods to do those operations but to actually BE an object that does
those doesn't make sense.
Using "is a/has a", I'd ask myself - IS Myclass a ValidHexStringChecker/StringToHexConverter?
If not, then revert to "has a", and add methods to do those operations, something like:
Class MyClass
{
public: //or protected or private
bool CheckValidHexString(...);
bool ConvertStringToHex(...);
};
ForNow wrote: Do I have to worry about the constructers of all 3 ??
If the base classes need construction with constructors that take passed parameters, then yes.
If the base classes have default constructors, and that's the only constructor needed, then no.
ForNow wrote: and can myClass get at the protected members of classb and CLassa
Yes, because you've specified public access to the base classes (see Controlling Access to
Class Members[^]).
I hope at least a little of that made sense 
Mark
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
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While OO is neat and useful, don't let it over-complicate things (e.g., not everything has to be a class just because C++ is being used). Unless you can actually think of your "something" as an object (which you probably could), why not just make "is a valid Hex sting" and "convert that string to a Hex" into just plain functions? The former could easily be done with strtol().
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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I was thinking - atoi - However I really realy want to learn C++
If you have any suggestions please let me know
thankx
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ForNow wrote: I was thinking - atoi...
Well don't, since it will not work with base-16 numbers.
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Hello,
It is probably a very bad question I post but why not trying.
Actually I use a CListCtrl with Edit label mode set to true and I would like to input from within a row a member variable name or an object member name instead of inputting a value.
This variable name or object name will be passed as argument to a function.
Is there a simple solution to do it?
Thnks for your kind help.
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You want to be able to type in a variable name in the edit box?
If so, you'll need to write code (maybe in response to LVN_ENDLABELEDIT) to map the entered text
to a variable in your code.
Mark
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
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Mark,
Thnks for your help.
yes I want to type in a variable name in the edit box.
could you please be more explicit about mapping the entered text?
Do you mean that I must store the variable name and a string of a same name as the variable in a CMap or std::map and to compare the entered text with the string in the map?
If the string is found I then get the variable related to the string?
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Sure, you could use a map. If there was only a few possibilities you could even use
if/else if/else if you wanted to
Mark
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
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Hi All
i want to get Unique Id of a particular device connected through USB \FIRWIRE Port.
IS Serial number unique? so how will i find find it of a device (like digital camera,scanner etc.)
i am able to get serial number of storage device(like USB flash Key, eternal Hard disk).
With Regards
RYK
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I have this UI issue causing my application to hang and I am absolutely clueless what is causing the hang.
From the callstack I find that it waits at ntdll, using SPY++ I find no messages being recieved by the application. It is also not a crash as the frame messages are being recieved but the opened document is frozen.
Any clues about how to approach the problem??
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cpp_prgmer wrote: I have this UI issue causing my application to hang...
At what point?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Well it works fine handling mouse move message over a tree. But then when I click on the cross of my MDI to close a document, I have my appln prompt to ask for save changes. It is not able to even display the messagebox, and it is stuck at ntdll... no idea why?
Also strange is that this happens when the tree is expanded and i handle mouse move event... does not happen when I collapse the tree and try to close the document. Any clues??
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Can you more explain about your program?
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It sounds like a deadlock, do you have multiple threads ? Are you using SendMessage() to send a message from one thread to another ?
Check the callstacks of each thread ( assuming you have more than one).
If you are not getting full symbol info in the call stacks, then try setting up a symbol server before you debug, also make sure that your .pdb file is accessible.
regards
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I am not sure if this is happening... but I will check. The prob is with mouse move event over a tree, so in tree collapsed state it works fine but with tree expand state, i am not able to close my document...
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I have just found the root cause to this happening is that I am calling SetCapture and not allowing processing of any other message when tree is expanded...
Sorry for the trouble... Is there any function that can detect this and override the same when trying to close the document??
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This error occured when i was trying to create eLoader.dll from the
vcproject. Which i downloaded from eAccelerator project.
can anyone know where can i find this header file php.h....
KIRAN PINJARLA
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kiran.pinjarla wrote: can anyone know where can i find this header file php.h....
Are you sure it is not present on your machine?
kiran.pinjarla wrote: Which i downloaded from eAccelerator project.
Is it a Windows application?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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hey folks,
I wrote a little wrapper for the gsl-library and had to face a problem I never had expected (and never noticed before).
It's a simple class-question... So first the code:
<br />
class myClass<br />
{<br />
public:<br />
myClass();<br />
~myClass();<br />
myClass Testfunction();<br />
int val;<br />
};<br />
<br />
myClass::myClass()<br />
{<br />
val=0;<br />
}<br />
<br />
myClass::~myClass()<br />
{<br />
int t = 0;<br />
int h = t;<br />
this->val = val;<br />
cout << "Destructor called\n";<br />
}<br />
<br />
myClass myClass::Testfunction()<br />
{<br />
myClass newClass;<br />
newClass.val = 7;<br />
return newClass;<br />
}<br />
<br />
int main()<br />
{<br />
myClass A;<br />
myClass B;<br />
cout << "Calling test function\n";<br />
B = A.Testfunction();<br />
<br />
cout << "Print out value:\n";<br />
cout << B.val << "\n";<br />
<br />
<br />
cout << "Waiting for user...\n";<br />
cin.get();<br />
}<br />
Allright... actually there shouldn't be any destructor called BEFORE the cin.get().
The output is:
<br />
Calling test function<br />
Destructor called
Destructor called
Print out value:<br />
7<br />
Waiting for user...<br />
The Destructor is somehow called for the return value and I don't know why...
And even if I get an explanation... is there a way of not calling the destructor here? (Compiler setting???)
because I actually free some memory in my prog in the destructor and when the memory is freed I never get it back... 
any idea??
thx in advance
zqueezy
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The Testfunction returns myClass also.
newclass doesn't exist past the end of testfunction, so the function returns a copy of it... Temporary copy needs constructing, and (drumroll) destructing.
Try adding another member to myClass, and a constructor which assigns a random value to it. Then also spit it out in the destructor. See how its actually different myClass instances getting killed.
As to the avoidance? That all depends on what you were really trying to do. What you have posted is a very artificial example to show the "double" destructing, it doesn't show what you were trying to do when you ran into this issue.
And just in case this is homework, as least I've only done 50% of your work.
Iain.
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well, no it's no homework. I'm well aware of the fact that the copy-call is run for the object that went out of scope...
To make my example less artificial:
In gsl a matrix need allocation of memory (alloc) and freeing the memory, of course.
I tried to write a matrix-class which does the allocation in the constructor and which does the freeing in the destructor.
Now I wrote an operator function for the multiplication:
CMatrix CMatrix::operator *(const CMatrix& factorMatrix);
when I try to return the resulting matrix the destructor is called and the memory freed thus the matrix deleted and cannot be assigned with any operation like the operator=...
better?
zqueezy
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The "extra" destructor you're getting is because you're being nice and elegant and writing a * operator, which (quite correctly) returns an instance (albeit a temporary one) on CMatrix.
If the constructor / destructor is "expensive", then you're going to have to do it a different way.
class CMatrix
{
public:
....
BOOL Multiply (CMatrix const &lhs, CMatrix const &rhs)
{
if (!ValidToDoThisMaths (lhs, rhs))
return FALSE;
....
return TRUE;
}
....
};
void main ()
{
CMatrix A,B,C;
A.Create (blah);
B.Set (blah);
C.Multiply (A,B);
C.DoStuff ();
}
Its less elegant, but it would solve your problem.
It would also lose the ability to do:
D = A * B * C
but frankly, matrices are enough of a pain to work with [ (n x m) * (m x n) etc ] that that's probably not a huge loss.
I hope that helped,
Iain.
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zqueezy wrote: Allright... actually there shouldn't be any destructor called BEFORE the cin.get().
Of course it should.
zqueezy wrote: The Destructor is somehow called for the return value and I don't know why...
Because newClass went out of scope, and the destructor must be called in that case.
zqueezy wrote: is there a way of not calling the destructor here?
Rewrite the function like this:
void myClass::Testfunction(myClass& obj)
{
obj.val = 7;
}
Create the object before calling it, and pass it as the argument.
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when I do the whole thing as reference... why is the destructor called anyways... isn't the reference just an address?
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