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copied!<p>What is the definition of <code>grid</code> and how are you populating it? I bet you are doing it from the Animal constructor. At this time, the dynamic type of this is <code>Animal</code>, and not the type of the object that is eventually created.</p> <pre><code>Animal::Animal() { grid[i][j] = this; // the type of this is Animal } </code></pre> <p>Until the object is fully constructed, you cannot use the <code>this</code> pointer in a dynamic way, this includes calling virtual functions, or using the virtual function table.</p> <p>To be more specific, you need to postpone using the <code>this</code> pointer, that is to say, storing it in the <code>grid</code> array, until after the object is fully constructed.</p> <p>Here in the Animal constructor:</p> <pre><code>Animal::Animal(Savanna *savana, int x, int y) { this->savanna = savana; moved = false; breedTicks = 0; this->x=x; this->y=y; savanna->setAt(x,y,this); } </code></pre> <p>Note that you are calling <code>Savanna::setAt</code> with the <code>this</code> parameter. At this point, the dynamic type of <code>this</code> is Animal, not Wildebeest or some other thing. setAt does this:</p> <pre><code>void Savanna::setAt(int x, int y, Animal *anim) { if ((x>=0) && (x<SAVANNASIZE) && (y>=0) && (y<SAVANNASIZE)) { grid[x][y] = anim; } } </code></pre> <p>The value of <code>anim</code> is the this pointer from the Animal constructor.</p> <p>Note a few more things. When you are constructing the list of Wildebeest, you are causing a dangling pointer:</p> <pre><code>for ( i = 0; i < initialWildebeest; i++) { while (!placed) { int x = 1 + (rand() % 20); int y = 1 + (rand() % 20); if (!(w.getAt(x, y))){ **** Wildebeest fred(&w, x, y); placed = 1; } } placed = 0; } </code></pre> <p>The WildeBeest named <code>fred</code> will go out of scope on the next line and be destroyed. You need to allocate it dynamically via <code>new</code>:</p> <pre><code>for ( i = 0; i < initialWildebeest; i++) { while (!placed) { int x = 1 + (rand() % 20); int y = 1 + (rand() % 20); if (!(w.getAt(x, y))){ Wildebeest *fred = new Wildebeest(&w, x, y); placed = 1; } } placed = 0; } </code></pre> <p>In the destrcuctor of the Savanna, there is a matching call to delete so that we do not leak memory:</p> <pre><code>Savanna::~Savanna() { // Release any allocated memory int i,j; for (i=0; i<SAVANNASIZE; i++) { for (j=0; j<SAVANNASIZE; j++) { **** if (grid[i][j]!=NULL) delete (grid[i][j]); } } } </code></pre> <p>You will have exactly the same problem with the Lion instances as well.</p>

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