A virtual function question
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I've looked around trying to find this information, but there's nothing I can find that fits my situation. I have two separate classes: Print and PropertySheet that are part of a larger program. I didn't write the code for either one and making any radical changes is out. All I need to do is add a function to the PropertySheet class that will access the Print class and print out certain information obtained from PropertySheet. Here's the problem: All of the print functions in Print (such as starting a new document, starting a new page, etc) are virtual functions and I can't access them from the PropertySheet class. I've never cared for vf's and haven't worked with them or used them before, so I'm lost on how to do this. Here's the question: How can I access those virtual functions in Print from PropertySheet without re-writing the program (I just want to add the code to print in the PropertySheet class)? I apologize if this has been addressed before, but, as I said, I couldn't find anything for this situation. I appreciate any help and say thank you in advance anyone that responds.
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I've looked around trying to find this information, but there's nothing I can find that fits my situation. I have two separate classes: Print and PropertySheet that are part of a larger program. I didn't write the code for either one and making any radical changes is out. All I need to do is add a function to the PropertySheet class that will access the Print class and print out certain information obtained from PropertySheet. Here's the problem: All of the print functions in Print (such as starting a new document, starting a new page, etc) are virtual functions and I can't access them from the PropertySheet class. I've never cared for vf's and haven't worked with them or used them before, so I'm lost on how to do this. Here's the question: How can I access those virtual functions in Print from PropertySheet without re-writing the program (I just want to add the code to print in the PropertySheet class)? I apologize if this has been addressed before, but, as I said, I couldn't find anything for this situation. I appreciate any help and say thank you in advance anyone that responds.
If you can't access them, that probably means they are protected or private, not virtual, necessarily. If they are protected, derive a class from Print to gain access. Make sure this is the right thing to do, they are probably protected for a reason. bcemick wrote: I've never cared for vf's Why - do you hate object orientation ? Is it possible to put code that defines the interaction between these two objects into a third class, so that they don't become tightly coupled ? Christian Graus - Microsoft MVP - C++
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If you can't access them, that probably means they are protected or private, not virtual, necessarily. If they are protected, derive a class from Print to gain access. Make sure this is the right thing to do, they are probably protected for a reason. bcemick wrote: I've never cared for vf's Why - do you hate object orientation ? Is it possible to put code that defines the interaction between these two objects into a third class, so that they don't become tightly coupled ? Christian Graus - Microsoft MVP - C++
The functions I need to access are public and declared as virtual. That's the first thing I checked.
public: UINT virtual NewDocument();It's not that I hate object orientation; I've just never understood the point of virtual functions. I don't understand why you would want to use them. Christian Graus wrote: Is it possible to put code that defines the interaction between these two objects into a third class, so that they don't become tightly coupled ? Not at this time, although that is a possibility later on. For right now, though, I have to get it working this way. -
The functions I need to access are public and declared as virtual. That's the first thing I checked.
public: UINT virtual NewDocument();It's not that I hate object orientation; I've just never understood the point of virtual functions. I don't understand why you would want to use them. Christian Graus wrote: Is it possible to put code that defines the interaction between these two objects into a third class, so that they don't become tightly coupled ? Not at this time, although that is a possibility later on. For right now, though, I have to get it working this way. -
What do you mean by: I can't access them ? Compilation error/warning ? Failing assertion ? Crash ?
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My apologies; I should have been clearer on that point. When I click on the Print button on the property sheet, it gives me an access violation (Error code: 5) when I'm in debug mode.
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That's not a problem of virtual, private nor public function. Access violation means you violated the memory you accessed, i.e. address of memory wasn't valid.
Have you placed any breakpoints to determine exactly where the access violation occurs (When you try to call the function, or inside the function...may trying to manipulate another object that isn't there anymore). How does this Print Object get instantiated?
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The functions I need to access are public and declared as virtual. That's the first thing I checked.
public: UINT virtual NewDocument();It's not that I hate object orientation; I've just never understood the point of virtual functions. I don't understand why you would want to use them. Christian Graus wrote: Is it possible to put code that defines the interaction between these two objects into a third class, so that they don't become tightly coupled ? Not at this time, although that is a possibility later on. For right now, though, I have to get it working this way.bcemick wrote: Not at this time, although that is a possibility later on. For right now, though, I have to get it working this way. It's NEVER a good idea to 'do it this way for now and change to a good design later'. I suggest you stop coding and read a book called 'Code Complete'. Seriously. If the function is not pure virtual ( has no body for you to call anyhow ), I don't see why you can't call it.