如何正确存储多个实例对象？

Question

I am making an intermediate/advanced C++ program, a video game to be exact.

Lately I have been noticing that there is a good amount of memory being leaked, and I was wondering if maybe something is wrong with the way I am creating my instances.

Below is a summarized(but originally complex) class:

class theObject
{
 //Instance variables
 //Instance functions
};

With this object(along with any other objects that I am storing, I have an array index of every different variation template of theObject . That part is not important, but the way I am storing them(or in my opinion) is:

//NEWER VERSION WITH MORE INFO
void spawnTheObject()
{
 theObject* NewObj=ObjectArray[N];
 //I give the specific copy its individual parameters(such as its spawn location and few edited stats)
 NewObj->giveCustomStats(int,int,int,int);//hard-coded, not actual params
 NewObj->Spawn(float,float,float);
 myStorage.push_back(new theObject(*NewObj));
}


//OLDER VERSION
void spawnTheObject()
    {
     //create a copy of the arrayed object
     theObject* NewObj=new theObject(*ObjectArray[N]);
     //spawn the object(in this case it could be a monster), and I am spawning multiple copies of them obviously
     //then store into the storage object(currently a deque(originally a vector))
     myStorage.push_back(new theObject(*NewObj));
     //and delete the temporary one
     delete NewObj;
    }

I am currently using a deque(recently changed from using a vector) but I am seeing no difference in the memory usage. I have though found out from "comment tests" that these spawning functions I have are the reason for the memory leaks. Since this is the wrong way to create/spawn the instances, I was wondering if there is a better way to storing these objects.

tl;dr: What are some better objects to store a non-constant amount of objects and how?

Answer 1

I am guessing you never clear new spawn objects in myStorage that causes the memory to increase(as you refer to memory leak). If I am correct your myStorage is declared as below:

std::deque<theObject*> myStorage;

if you call either of below calls, the pointers to theObject are delete but the real dynamically allocated objects are not deleted.

 myStorage.pop_back();
 myStorage.clear();

Another small issue in your code, you are making unnecessary object allocate/dellocate in spawnTheObject() function.

How to clean container with pointer type

You need to iterate through each element in myStorage, delete the object then clear the container, for example:

for (std::deque<theObject*>::iterator iter=myStorage.begin();
     iter != myStorage.end(); ++iter)
{
   delete (*iter);
}
myStorage.clear();

Better solution:

Use smart pointers in std::deque or std::vector , then when you remove an element from STL container the object the pointer is pointing to is also deleted automatically.

 #include <memory>

 std::deque<std::shared_ptr<theObject> > myStorage;
 myStorage.push_back(std::shared_ptr<theObject>(new *ObjectArray[N]));

 mySorage.clear();  // all memories cleared properly, no worries

Answer 2

If you do not manually delete your objects from myStorage at the end of the game or when they need to be destroyed, there is your memory leak.

myStorage.push_back(new theObject(*NewObj));

The object being pushed into storage is allocated by you, so it should be destroyed by you when it needs to disappear.

Also I do not understand the need for the intermediate NewObj object, it isnt a memory leak but it is an unnecessary performance cost, 1 allocation/deallocation + 1 copy.

As Forever mentioned, your best bet is to start using smart pointers, either std::unique_ptr or std::shared_ptr (only if c++11).