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POPolymorphism and array of pointers problem in C++
 

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  1. POPolymorphism and array of pointers problem in C++
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    <p>I'm working on a project and it's in a stage that I don't know what's wrong. Here's the simplified version:</p> <p>The code:</p> <pre><code> class Base { // This base class is pure abstract public: virtual ~Base(); // Necessary to trigger destructors in inherited classes virtual baseFunc() = 0; }; class DerivedA : public Base{ public: DerivedA(SomeClassUseBase * tmp){ tmp -&gt; register(this); } ~DerivedA(); void baseFunc(){ // do something here that's only for DerivedA } }; class DerivedB : public Base{ public: DerivedB(SomeClassUseBase * tmp) { tmp -&gt; register(this); } ~DeriveB(); void baseFunc(){ // do something here that's only for DerivedB } }; class SomeClassUseBase { private: Base ** basePrt; unsigned int index; public: someClassUseBase(int num) { basePrt = new Base*[num]; //create an array of pointers to the objects index = 0; } void register( Base * base ){ //i tried *(basePrt[index]) = *base, but got the same problem basePrt[index] = base; index = index + 1; } void checkList() { for (int i = 0; i &lt; index ;i++){ next = basePrt[i]; next -&gt; baseFunc(); //fails here } } }; int main() { SomeClassUseBase tmp = new SomeClassUseBase(5); Base *b[5]; for ( i = 0; i &lt; 5; i += 1 ) { if ( i % 2 == 0 ) { b[i] = new DerivedA(&amp;tmp); } else { b[i] = new DerivedB(&amp;tmp); // the object pointed by tmp::basePrt[0] is lost after this line } // if } // for tmp.checkList(); //crashes here since tmp.bastPrt[0] points to null } </code></pre> <p>The problem is that when in main, i reach the line when the first DerivedB is created, the already created DerivedA pointer by tmp.basePrt[0] is lost some how. I don't know why but i suspect that this has sth to do with polymorphism? Please help!! thanks!!</p> <p>Edit:</p> <p>Didn't quite get the code correct the first time, sorry... </p>
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    1. COJust to add some details to the question: an object of SomeClassUseBase will keep an array of ptr to objects from base class, which in runtime will be either DerivedA ptr or DerivedB ptr. The reason calling tmp.register(this) is adding self to that list. And btw, tmp has a public function Base **getTheList(); , which will return the array of pointers to Base objects, again (those will be pointers to DerivedA/B at runtime)
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    2. COThe code, as presented, doesn't compile. Fixing the compiler errors and running it does not exhibit the problem you're experiencing. Perhaps you should check that the example you give demonstrates the problem you're having.
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      1. USSkizz
 

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