Re: How to assign value to a variable without using a function?

"Allan" <test@test.com> ha scritto nel messaggio
news:e7tELkKQKHA.5108@TK2MSFTNGP02.phx.gbl...


First of all, I would define the temperature data member *private* in the
class, e.g.

class CTest
{
 ...
 private:
    int temperature_ ;
};

As a naming convention, I like to identify data members and differentiate
them from local variables by using an "m_" prefix (e.g. 'm_temperature')
or underscore postfix (e.g. 'temperature_').

Then, I would define a couple of get/set public methods to change the
value of the data member, e.g. GetTemperature and SetTemperature.
If these methods are made by few lines of code, you could declare them as
'inline', so the compiler could generate an optimized code (avoiding
function calling overhead).
These getter/setter methods can be called also by derived classes to
change the value of the data member (but derived classes can't access the
data member directly, because the data member is defined private).

In this way, you can do:

 CTest test;
 test.SetTemperature( 30 );
 ...
 int temperature = test.GetTemperature();

If you want the C#-like syntax typical of properties, you can use a
Microsoft specific extension to C++:

__declspec(property) attribute
http://msdn.microsoft.com/en-us/library/yhfk0thd.aspx

In this case, you just need to add a line like this in the class
definition:

   __declspec( property( get=GetTemperature, put=SetTemperature ) ) int
Temperature;

The compiler will automagically call the GetTemperature or SetTemperature
methods for you, whenever you access the Temperature "virtual data
member".

With this feature, you can write code like this:

<code>

   TestClass c;
   c.Temperature = 20; // SetTemperature is called
   cout << "Current temperature is " << c.Temperature /* GetTemperature is
called */ << endl;
   c.Temperature = 200;
   cout << "Current temperature is " << c.Temperature << endl;

</code>

You can see a compilable sample code below.

If you must use standard-compliant C++, I think that you don't have this
"syntactic sugar" available.

HTH,
Giovanni

<code>
//////////////////////////////////////////////////////////////////////////
// Test.cpp

#include <iostream>

//------------------------------------------------------------------------
// CLASS DECLARATION
//------------------------------------------------------------------------

// This class has a property called "Temperature".
class TestClass
{
public:

   TestClass();

   void SetTemperature(int temperature);
   int GetTemperature() const;

   __declspec( property( get=GetTemperature, put=SetTemperature ) ) int
Temperature;

private:
   int temperature_;
};

//------------------------------------------------------------------------
// INLINE METHOD IMPLEMENTATIONS
//------------------------------------------------------------------------

inline int TestClass::GetTemperature() const
{
   return temperature_;
}

//------------------------------------------------------------------------
// METHOD IMPLEMENTATIONS
//------------------------------------------------------------------------

TestClass::TestClass()
: temperature_(0)
{
}

void TestClass::SetTemperature(int temperature)
{
   temperature_ = temperature;
   if (temperature > 100)
   {
       std::cout << "Temperature > 100" << std::endl;
   }
   else
   {
       std::cout << "Temperature <= 100" << std::endl;
   }
}

//------------------------------------------------------------------------
// TEST
//------------------------------------------------------------------------

int main()
{
   using std::cout;
   using std::endl;

   TestClass c;
   c.Temperature = 20;
   cout << "Current temperature is " << c.Temperature << endl;
   c.Temperature = 200;
   cout << "Current temperature is " << c.Temperature << endl;

   return 0;
}

//////////////////////////////////////////////////////////////////////////

</code>