Skip to main content

A STL vector usage through shared_ptr

We know vector can store homogeneous kind of stuff. That is, it can store type int, string etc individually but not element of type int with string etc.

However, sometimes we might have requirements that it can store elements which are in inheritance relation and can do stuff by calling function of respective element stored in vector. As an example, I've a Shape class from which I've derived Circle, Polygon etc. Now I want to store Circle, Polygon object in a vector and then access each element by its iterator and draw shape accordingly.

C++ 2011 made it possible via shared_ptr. Thanks to Stephan aka STL.

Code snippet

#include < iostream >
#include < memory >
#include < vector >

using namespace std;

class Shape
{
public:
    Shape(){}
    virtual ~Shape(){}

    virtual void draw(int x, int y)
    {
        cout << "Shape::draw(" << x << ", " << y << ")" << endl;
    }

private:
    Shape(const Shape&);
    Shape& operator=(const Shape&);
};

class Circle : public Shape
{
public:
    virtual void draw(int x, int y) override
    {
        cout << "Circle::draw(" << x << ", " << y << ")" << endl;
    }
};

class Polygon : public Shape
{
public:
    virtual void draw(int x, int y)
    {
        cout << "Polygon::draw(" << x << ", " << y << ")" << endl;
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    vector< shared_ptr< Shape > >vec;

    shared_ptr< Shape > shape = make_shared< Polygon >();
    vec.push_back(shape);

    shape = make_shared< Circle >();
    vec.push_back(shape);

    vec.at(0)->draw(11, 22);
    vec.at(1)->draw(33, 44);

    return 0;
}

I've used Visual Studio 2010 to build this code. And output will be:
Polygon::draw(11, 22)
Circle::draw(33, 44)

Comments

Post a Comment

Popular posts from this blog

XOR (Exclusive OR) for branchless coding

The following example shows the array reversing using the  XOR operator . No need to take any additional variable to reverse the array.   int main(int argc, _TCHAR* argv[]) { char str[] = "I AM STUDENT"; int length = strlen(str); for(int i = 0; i < ((length/2)); i++) { str[i] ^= str[length - (1+i)]; str[length - (1+i)] ^= str[i]; str[i] ^= str[length - (1+i)]; } cout << str << endl; return 0; } The above example is one of the uses of XOR but XOR comes in handy when we can do branchless coding  methods like butterfly switch etc. Sometimes this is very effective in speeding up the execution.  Let's see one of the uses of XOR in branchless coding. I am taking a simple example of Y = | X |.  Yes, I am generating abs of a supplied number. So, my function signature/definition in C++ looks like below: int absoluteBranch( int x) {     if (x < 0 ) {         return ...
1 comment
Read more

Power of Two

  I n this post will be discussing how to calculate if a number is a power of two or not. As an example, 8 is a power of two but the number 10 is not. There are many ways we can solve this. First , we will take an approach which is simple and iterative. In this case, we will calculate the power of two one by one and check with the supplied number. The below code illustrates it. bool isPowerofTwo(unsigned num) { auto y = 1; while (0 != y) { if (num == y) return true; if (num < y) return false; y <<= 1; } return false; } Second , assuming, the number is a 32-bit number, this is also an iterative solution. In this scenario, iterating all bits and counting the set bits. Any number which is a power of 2 will have only one bit set and the rest will be zeros. As an example, 8 in binary representation is 1000. Using this observation, we can implement an iterative solution. bool isPowerofTwo(unsigned num) { auto one_count = 0; for (auto index = 0; index < ...
Post a Comment
Read more

Reversing char array without splitting the array to tokens

 I was reading about strdup, a C++ function and suddenly an idea came to my mind if this can be leveraged to aid in reversing a character array without splitting the array into words and reconstructing it again by placing spaces and removing trailing spaces. Again, I wanted an array to be passed as a function argument and an array size to be passed implicitly with the array to the function. Assumed, a well-formed char array has been passed into the function. No malformed array checking is done inside the function. So, the function signature and definition are like below: Below is the call from the client code to reverse the array without splitting tokens and reconstructing it. Finally, copy the reversed array to the destination.  For GNU C++, we should use strdup instead _strdup . On run, we get the following output: Demo code
Post a Comment
Read more