Using Properties in Your C Classes

I l @ ve RuBoard

Using Properties in Your C++ Classes

Properties are pseudo-data members of your classes. They are accessed just like public data members but in reality they are functions within the class.

Adding properties to Garbage Collected C++ classes is accomplished by the use of the __property keyword. Listing 1.4.14 shows a simple GC class with properties.

Listing 1.4.14 props.cpp : Simple Properties in a GC Class

 #using <mscorlib.dll> using namespace System; using namespace System::IO; __gc class PropClass {     int m_x;     int m_y;     int m_z; public:     PropClass() : m_y(19762), m_z(3860)     {     }     // read / write properties for a data member     __property int get_x(){ return m_x;}     __property void set_x(int v){ m_x=v;}     // read only properties for a data member     __property int get_y(){ return m_y;}     // write only properties for a data member     __property void set_z(int v){ m_z=v;}     // properties that don't act on data at-all     __property int get_bogus()     {         Console::WriteLine("Read the bogus property!");         return 10;     }     __property void set_bogus(int v)     {         Console::WriteLine("Wrote { 0}  to the bogus property!",__box(v));     }     String* ToString()     {         StringWriter *w=new StringWriter();         w->Write("PropClass; m_x = { 0} , m_y = { 1} , m_z = { 2} ",__ box(m_x), __  box(m_y), __box(m_z));         return w->ToString();     } }; void main() {     PropClass *pP=new PropClass();     Console::WriteLine("At Creation...{ 0} ",pP);     pP->x=50;     Console::WriteLine("Wrote to x...{ 0} ",pP);     pP->z=100;     Console::WriteLine("Wrote to z...{ 0} ",pP);     pP->bogus = 150;     Console::WriteLine(pP);     int x=pP->x;     Console::WriteLine("Read x, Return ={ 0} , { 1} ",__box(x),pP);     int y=pP->y;     Console::WriteLine("Read y. Return ={ 0} , { 1} ",__box(y),pP);     int z=pP->bogus;     Console::WriteLine("Returned value = { 0} ,  { 1} ",__box(z),pP); } 

The props.cpp program shows properties that directly access data members within a class and properties that perform some computation that is not necessarily related to class attributes at all.

The program also shows the technique of creating read-only or write-only properties. To create a read-only property, simply include only the get_ accessor. Write-only properties have only set_ accessors.

Finally, the program shows the interesting technique of overriding the ToString() method. Remember that classes declared with __gc are derived implicitly from System::Object . This class defines the ToString method, which is used to output a text representation of the class to text streams.

I l @ ve RuBoard