How to free the pointer which allocated on the heap, use different method !

Learning STL 02.md

• when using containers of newed pointers, remember to delete the pointers before the container is destroyed.

void doSomething() {
	vector<Widget*> vwp;
	for(int i=0;i<NUMS;++i) {
		vwp.push_back(new Widget);
	}
}
// Widgets are leaked here !

• you should delete the memory which you allocate

void doSomething() {
	vector<Widget*> vwp;
	for(int i=0;i<NUMS;++i) {
		vwp.push_back(new Widget);
	}
	//////// do something
	for(vector<Widget*>::iterator it=vwp.begin(); it!=vwp.end(); ++it) {
		delete *it;
	}
}

• you can also use for_each to free the memory

template<typename T>
struct DeleteObject {
	public unary_function<const T*, void> {
		void operator()(const T *ptr) const {
			delete ptr;
		}
	}
};

Now you can do this:

void doSomething() {
	... // as before
	for_each(vwp.begin(), vwp.end(), DeleteObject<Widget>);
}

• you can also use another defination to simplify the maintain

struct DeleteObject {
	template<typename T>
	void operator()(const T* ptr) const {
		delete ptr;
	}
};

void doSomething() {
	deque<SpecialString*> dssp;
	... //fill the containers
	for_each(dssp.begin(), dssp.end(), DeleteObject()); 
	// ah! well-defined behavior, Straightforward and type-safe, just the wat we like it.
}

• Use Smart Pointer to revoke the memory

void doSomething() {
	typedef std::shared_ptr<Widget> SPW;
	vector<SPW> vwp;
	for(int i=0;i<NUMS;++i) {
		vwp.push_back(SPW new Widget);
	}
}
// No Widgets are leaked here, not even if an exception is thrown in the code above