Click here to Skip to main content
Click here to Skip to main content

The Microsoft VC++ Virtual Property feature

, 6 Jan 2000
Rate this:
Please Sign up or sign in to vote.
Using the __declspec(property) method to enhance legacy code
<!-- Article Starts -->

A lot of legacy C++ code exists wherein member variables are directly exposed using the public or protected keywords instead of simple accessor / mutator functions. For example consider the following simple structure definition

typedef struct tagMyStruct 
{ 
   long m_lValue1; 
   ...             // Rest of the structure definition. 
} SMyStruct; 

Scattered throughout the client code that uses this structure will be code like the following:

SMyStruct       MyStruct; 
long            lTempValue; 

MyStruct.m_lValue1 = 100;       // Or any other value that is to be assigned to it. 
... 
lTempValue = MyStruct.m_lValue1; 

Now if the module that has all the above code is suddenly required to be used in a thread safe environment, you run into a problem. Because no accessor or mutator functions exist, you cannot just put a critical section (or mutex) within the definition of SMyStruct and protect m_lValue1 or any of the other public member variables.

If it is guaranteed that you will be using the Microsoft Visual C++ compiler then there is an easy solution at hand.

Just enhance the structure as follows:

typedef struct tagMyStruct 
{ 
   __declspec(property(get=GetValue1, put=PutValue1))

   long  m_lValue1; 
   ...                // Rest of the structure definition. 

   long GetValue1() 
   { 
      // Lock critical section 

      return m_lInternalValue1; 

      // Unlock critical section. 
   } 

   void PutValue1(long lValue) 
   { 
      // Lock critical section 

      m_lInternalValue = lValue; 

      // Unlock critical section 
   } 

private: 
        long m_lInternalValue1; 

        // Define critical section member variable. 
} SMyStruct; 
That's all.

For code such as

MyStruct.m_lValue1 = 100
the compiler will automatically substitute
MyStruct.PutValue1(100)

For code like

lTempValue = MyStruct.m_lValue1
the compiler will substitute
lTempValue = MyStruct.GetValue1()

The possibilities this opens up are many. You can even use this to add reference counting to legacy structures and classes.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Jeremiah Talkar

United States United States
No Biography provided

Comments and Discussions

 
GeneralAnybody help pls Pinmemberbeatselva14-Dec-04 20:02 
Generalmore info on __declspec(property) PinmemberTemplMetaProg3-Jul-02 10:56 
GeneralInfinte Array PinmemberFahad22-Jul-01 15:16 
GeneralRe: Infinte Array PinmemberTemplMetaProg3-Jul-02 10:54 
GeneralRe: Infinte Array Pinmemberdhumalswati23-Aug-03 0:08 
GeneralThere is a second way to do it PinsussMh2x24-Aug-00 14:42 
GeneralRe: There is a second way to do it PinmemberAli Demir8-Jan-01 22:41 
GeneralRe: There is a second way to do it PinmemberDmitry Sychov27-Aug-01 2:13 
GeneralA set of questions about this code -> PinsussAsaf Karass15-Jul-00 2:14 
GeneralRe: A set of questions about this code -> PinsussJeremiah S. Talkar17-Jul-00 4:57 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Mobile
Web02 | 2.8.140709.1 | Last Updated 7 Jan 2000
Article Copyright 2000 by Jeremiah Talkar
Everything else Copyright © CodeProject, 1999-2014
Terms of Service
Layout: fixed | fluid