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POAccessing Properties/Functions of Subclasses C++
 

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  1. POAccessing Properties/Functions of Subclasses C++
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    <p>I am having a design problem in my program because I need to occasionally access properties &amp; methods of subclasses that are all stored in a vector of base class pointers. My code looks something like this:</p> <pre><code>class B1; class B2; class Base { private: int id, a, b; public: virtual int getA() { return a; } virtual int getB() { return b; } virtual B1 *getB1() { return NULL; } //seems like a bad idea virtual B2 *getB2() { return NULL; } //to have these two functions Base(int newId) { id = newId; } }; class B1 : public Base { private: int x; public: int getX() { return x; } B1 *getB1() { return this; } }; class B2 : public Base { private: int y; public: int getY() { return y; } B2 *getB2() { return this; } }; class Thing { private: std::vector&lt;Base*&gt; bases; void addBase(Base *base) { bases.push_back(base); } void doB1Stuff(); void doB2Stuff(); void setAandB(int ID, int newA, int newB); //set a and b of one of the elements in bases vector based upon the id given }; </code></pre> <p>The problem is if I need to access x or y in Thing, like this below:</p> <pre><code>void Thing::doB1Stuff() { for(std::vector&lt;Base*&gt;::iterator it = bases.begin(); it != bases.end(); ++it) { if (it-&gt;getB1()) { //do stuff with b1 } } } </code></pre> <p>The code above should work, but if it seems a bad idea because one could easily forget to check if the pointer is null before using B1/B2 properties like this:</p> <pre><code>void Thing::doB2Stuff() { for(std::vector&lt;Base*&gt;::iterator it = bases.begin(); it != bases.end(); ++it) { std::cout &lt;&lt; it-&gt;getY(); //I believe this will crash the program if a NULL pointer is returned } } </code></pre> <p>My question thus is: what is a good way of accessing subclass properties? I was thinking of having two separate vectors for B1s and B2s in Thing, but that doesn't seem like a good idea either because I need to be able to set a and b easily. Any thoughts?</p>
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    1. COIf your classes are behaving fundamentally differently in that context, you shouldn't be mixing them in the array. Maybe you want to use a template instead?
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    2. COYour precise problem is solved with `dynamic_cast`. (Or a better design)
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      1. USDrew Dormann
 

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