Strange errors: EXC_BAD_ACCESS in my class - c++

Question

Here is my code:
typedef struct TItemSelector{
ItemSelectFrame* pItems[2];
} SItemSelector;
class item {
public:
void expMethod();
SItemSelector itemSelector_;
UILayerButton* startBtn_;
};
void item::expMethod(){
startBtn_ = new UILayerButton();
for (i = 0; i < 3; i++) {
itemSelector_.pItems[i] = new ItemSelectFrame();
}
startBtn_->callMethodA();
}
void UILayerButton::callMethodA()
{
this->callMethodB();
}
void UILayerButton::callMethodB()
{
}
On this->callMethodB();, a "EXC_BAD_ACCESS" occoured.
After that I found a work-around:
class item {
public:
void expMethod();
SItemSelector itemSelector_;
SItemSelector itemSelector2_; // work around
UILayerButton* startBtn_;
};
Then everything goes well... I just don't know what happened, but callMethodB() is just an empty method, there's nothing to do with it.
I'm using Apple LLVM 3.1, default setting.
UPDATE: Fixed my code.

Answer 1

In this code:
for (i = 0; i < 3; i++) {
itemSelector_.pItems[i] = new ItemSelectFrame();
}
you are writing over the end of itemSelector_.pItems because pItems is an array of length 2 but you are writing 3 elements.
That then overwrites startBtn_ which happens to appear immediately after itemSelector_ in memory. And that explains the error when you subsequently read the now corrupted startBtn_.
Either change your loop termination test, or increase the length of pItems. I can't tell which one is the correct solution, but clearly you will know.