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The Microsoft VC++ Virtual Property feature

, 6 Jan 2000
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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

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About the Author

Jeremiah Talkar
United States United States
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Comments and Discussions

 
GeneralAnybody help pls Pin
beatselva14-Dec-04 20:02
memberbeatselva14-Dec-04 20:02 
Generalmore info on __declspec(property) Pin
TemplMetaProg3-Jul-02 10:56
memberTemplMetaProg3-Jul-02 10:56 
GeneralInfinte Array Pin
Fahad22-Jul-01 15:16
memberFahad22-Jul-01 15:16 
GeneralRe: Infinte Array Pin
TemplMetaProg3-Jul-02 10:54
memberTemplMetaProg3-Jul-02 10:54 
GeneralRe: Infinte Array Pin
dhumalswati23-Aug-03 0:08
memberdhumalswati23-Aug-03 0:08 
GeneralThere is a second way to do it Pin
Mh2x24-Aug-00 14:42
sussMh2x24-Aug-00 14:42 
GeneralRe: There is a second way to do it Pin
Ali Demir8-Jan-01 22:41
memberAli Demir8-Jan-01 22:41 
GeneralRe: There is a second way to do it Pin
Dmitry Sychov27-Aug-01 2:13
memberDmitry Sychov27-Aug-01 2:13 
GeneralA set of questions about this code -> Pin
Asaf Karass15-Jul-00 2:14
sussAsaf Karass15-Jul-00 2:14 
GeneralRe: A set of questions about this code -> Pin
Jeremiah S. Talkar17-Jul-00 4:57
sussJeremiah S. Talkar17-Jul-00 4:57 
GeneralRE: Do not use this if possible Pin
Llew Goodstadt20-Jan-00 7:56
sussLlew Goodstadt20-Jan-00 7:56 
GeneralRe: RE: Do not use this if possible Pin
Jeremiah S. Talkar21-Jan-00 8:46
sussJeremiah S. Talkar21-Jan-00 8:46 
GeneralRe: RE: Do not use this if possible Pin
Phil Harding14-Mar-05 22:09
memberPhil Harding14-Mar-05 22:09 
GeneralDo not use this if possible Pin
Llew17-Jan-00 23:47
sussLlew17-Jan-00 23:47 
GeneralRe: Do not use this if possible Pin
Chris Maunder18-Jan-00 12:36
sussChris Maunder18-Jan-00 12:36 
GeneralRe: Do not use this if possible Pin
Jeremiah S. Talkar19-Jan-00 18:17
sussJeremiah S. Talkar19-Jan-00 18:17 
Generala doubt on The Microsoft VC++ Virtual Property feature Pin
Vivek Medhekar17-Jan-00 22:00
sussVivek Medhekar17-Jan-00 22:00 
GeneralRe: a doubt on The Microsoft VC++ Virtual Property feature Pin
Jeremiah S. Talkar19-Jan-00 17:33
sussJeremiah S. Talkar19-Jan-00 17:33 
GeneralRe: a doubt on The Microsoft VC++ Virtual Property feature Pin
Vitaly A. Brusentsev19-Jan-00 22:31
sussVitaly A. Brusentsev19-Jan-00 22:31 
GeneralRe: a doubt on The Microsoft VC++ Virtual Property feature Pin
Jeremiah S. Talkar21-Jan-00 8:56
sussJeremiah S. Talkar21-Jan-00 8:56 
GeneralRe: a doubt on The Microsoft VC++ Virtual Property feature Pin
Jeremiah S. Talkar22-Jan-00 9:54
sussJeremiah S. Talkar22-Jan-00 9:54 
GeneralRe: a doubt on The Microsoft VC++ Virtual Property feature Pin
Jeremiah Talkar9-Apr-01 8:05
memberJeremiah Talkar9-Apr-01 8:05 
GeneralRe: a doubt on The Microsoft VC++ Virtual Property feature Pin
nagip almoshaki9-Jun-02 8:32
membernagip almoshaki9-Jun-02 8:32 
GeneralMessage Automatically Removed Pin
12-Jan-00 11:14
sussSandeep Bhatia12-Jan-00 11:14 
GeneralMessage Automatically Removed Pin
11-Jan-00 16:51
sussGeorge Poulose11-Jan-00 16:51 

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