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What is Proxy Class in C++?
Here we will see what is the proxy class in C++. The Proxy class is basically the Proxy design pattern. In this pattern an object provides a modified interface for another class. Let us see one example.
In this example, we want to make an array class, that can store only binary values [0, 1]. This is the first try.
Example Code
class BinArray {
int arr[10];
int & operator[](int i) {
//Put some code here
}
};In this code, there is no condition checking. But we want the operator[] to complain if we put something like arr[1] = 98. But this is not possible, because it is checking the index not the value. Now we will try to solve this using proxy pattern.
Example Code
#include <iostream>
using namespace std;
class ProxyPat {
private:
int * my_ptr;
public:
ProxyPat(int& r) : my_ptr(&r) {
}
void operator = (int n) {
if (n > 1) {
throw "This is not a binary digit";
}
*my_ptr = n;
}
};
class BinaryArray {
private:
int binArray[10];
public:
ProxyPat operator[](int i) {
return ProxyPat(binArray[i]);
}
int item_at_pos(int i) {
return binArray[i];
}
};
int main() {
BinaryArray a;
try {
a[0] = 1; // No exception
cout << a.item_at_pos(0) << endl;
}
catch (const char * e) {
cout << e << endl;
}
try {
a[1] = 98; // Throws exception
cout << a.item_at_pos(1) << endl;
}
catch (const char * e) {
cout << e << endl;
}
}Output
1 This is not a binary digit
Updated on: 30-Jul-2019
1K+ Views
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