Skip to main content

C++ property and detection of property change event

In C++, property means a private field with a getter and a setter method. Unlike C# and other languages, it is part of the language where it is set or accessed just like a field. In C++ never had the notion of the way C# address gets or set of property field(s).

However, in MSVC, Clang a property extension has been added to give a notion of get / set of property. How it looks like? Let's have a small code: 

#include <iostream>
#include <string>

using std::cout;
using std::string;

class Animal
{
    string sName_;

public:
    string getName() const { return sName_; }
    void setName(const string &asName)
    {
        sName_ = asName;
    }

public:
    __declspec(property(get = getName, put = setName)) string sName;
};

int main()
{
    Animal aObj;
    // Set animal name
    aObj.sName = "Cat";
    cout << "The animal is: " << aObj.sName << "\n";
}

The __declspec extension uses the get and set methods, and these two methods have to be public.

One can argue the usage of properties can also be done through getter and setter methods. Then why to use __declspec properties. This can help us to detect an event on property change. This is nicely shown by  Dmitri Nesteruk in his youtube video. However, the following code snippet is showing same along with some modifications (Compiles in MSVC 2022): 

#include <iostream>
#include <string>

#include <boost/signals2/signal.hpp>

using std::cout;
using std::string;
using boost::signals2::signal;

template<typename T>
class INotifyPropertyChange
{
public:
    signal<void(T*, string, string)> PropertyChanged;
};

class Animal : public INotifyPropertyChange<Animal>
{
    string sName_;

public:
    string getName() const { return sName_; }
    void setName(const string &asName) 
    {
        if (asName == sName_) return;
        if (sName_.empty())
        {
            sName_ = asName;
            return;
        }
        string localName = sName_;
        sName_ = asName;
        PropertyChanged(this, localName, asName);
    }

public:
    __declspec(property(get = getName, put = setName)) string sName;
};

int main()
{
    Animal aObj;
    boost::signals2::connection aConnObj = aObj.PropertyChanged.connect([](Animal* pAnimal, string aOldName, string aNewName)
        {
            cout << "Animal name has changed from: " << aOldName << " to " << aNewName << "!\n";
        });
    aObj.sName = "Cat";
    aObj.sName = "Dog";
    aObj.sName = "Horse";
    aConnObj.disconnect(); // Once disconnected no more notification 
                                           //  gets generated for property change

    aObj.sName = "Squirrel";
}

Output: 



Labels:

Comments

Post a Comment

Popular posts from this blog

Variadic template class to add numbers recursively during compilation

 The idea of having a class to add numbers (variable parameters) during compilation time recursively. Also wanted to restrict types to a single type while sending parameters to class member function. That said, if we mix int, float and double types to add function shall result in compilation error. How do we achieve this. The below is the code which actually helps to achieve this: <code> #include < fmt/format.h > template < typename T> class MyVarSumClass{     private :         T _sum = 0 ;     public :         template < typename ... TRest>         T add(T num, TRest... nums){             static_assert (std::conjunction<std::is_same<TRest, T>...>{}); /* Assert fails                if types are different */             _sum += num;             return add(nums...); // Next parameter packs gets picked recursively         }         // Base case         T add(T num){             _sum += num;             return _sum;         } }; int main() {     My
Post a Comment
Read more

A simple approach to generate Fibonacci series via multi-threading

T his is a very simple approach taken to generate the Fibonacci series through multithreading. Here instead of a function, used a function object. The code is very simple and self-explanatory.  #include <iostream> #include <mutex> #include <thread> class Fib { public:     Fib() : _num0(1), _num1(1) {}     unsigned long operator()(); private:     unsigned long _num0, _num1;     std::mutex mu; }; unsigned long Fib::operator()() {     mu.lock(); // critical section, exclusive access to the below code by locking the mutex     unsigned long  temp = _num0;     _num0 = _num1;     _num1 = temp + _num0;     mu.unlock();     return temp; } int main() {     Fib f;          int i = 0;     unsigned long res = 0, res2= 0, res3 = 0;     std::cout << "Fibonacci series: ";     while (i <= 15) {         std::thread t1([&] { res = f(); }); // Capturing result to respective variable via lambda         std::thread t2([&] { res2 = f(); });         std::thread t3(
Post a Comment
Read more

A concept to a product (Kimidori [ 黄緑]) - Part 2

In the previous part , we have seen KIMIDORI [ 黄緑] detect if a URL is malicious. In this part, we will see the details that KIMIDORI [ 黄緑] fetches out of the URL provided. As an example, provided a safe URL, https://www.azuresys.com/, and let's see what it brings out: As we can see, the link is safe and the link is active, which means we can just click on the link to open it on IE.  Now it's time to look into the URL report (still under development):  We have URLs IP, Location, and HTTP Status code. The Report part is a sliding window, the Show Report button shows as well as hides the report. Show / Hide Report is a toggle button. Let's see if we get the same details for any bad (phishing / malicious) URL: Took an URL example from a phishing link and tested it. The tool detected it as not a good link (Screen Shot Below) & link does not activate unlike a safe URL: Now let's see the report part for more details including domain registration details: It looks like it&
Post a Comment
Read more