C++ delete vector, objects, free memory

c++ vector delete-operator
mister picture mister · May 5, 2012 · Viewed 176.4k times · Source

I am totally confused with regards to deleting things in C++. If I declare an array of objects and if I use the clear() member function. Can I be sure that the memory was released?

For example : 

tempObject obj1;
tempObject obj2;
vector<tempObject> tempVector;

tempVector.pushback(obj1);
tempVector.pushback(obj2);

Can I safely call clear to free up all the memory? Or do I need to iterate through to delete one by one?

tempVector.clear();

If this scenario is changed to a pointer of objects, will the answer be the same as above?

vector<tempObject> *tempVector;
//push objects....
tempVector->clear();

Answer

Benjamin Lindley picture Benjamin Lindley · May 5, 2012

You can call clear, and that will destroy all the objects, but that will not free the memory. Looping through the individual elements will not help either (what action would you even propose to take on the objects?) What you can do is this:

vector<tempObject>().swap(tempVector);

That will create an empty vector with no memory allocated and swap it with tempVector, effectively deallocating the memory.

C++11 also has the function shrink_to_fit, which you could call after the call to clear(), and it would theoretically shrink the capacity to fit the size (which is now 0). This is however, a non-binding request, and your implementation is free to ignore it.

Related questions

What is the right way to free a std::vector of pointers in C++?

I searched StackOverflow but couldn't find the answer to this question. Suppose I have a std::vector<Day *> vector_day - that is - a vector of pointers to Day object. Now I push_back to vector_day …

Read More
Deleting vector of pointers

I need to create pointers of instances of a class, and the program do not know at compilation time how many pointers I will create. For deletion, I was considering storing the pointers in a vector, and then deleting them …

Read More
How to find out if an item is present in a std::vector?

All I want to do is to check whether an element exists in the vector or not, so I can deal with each case. if ( item_present ) do_this(); else do_that();

Read More