Delete parts of a dynamic array and grow other

I need to have a dynamic array, so I need to allocate the necessary amount of memory through a pointer. What makes me wonder about which is a good solution, is that C++ has the ability to do something like:

int * p = new int[6];

which allocates the necessary array. What I need is that, afterwards, I want to grow some parts of this array. A(n flawed) example:

int *p1 = &p[0];
int *p2 = &p[2];
int *p3 = &p[4];
// delete positions p[2], p[3]
delete [] p2;
// create new array
p2 = new int[4];

I don't know how to achieve this behavior.

EDIT: std::vector does not work for me since I need the time of insertion/deletion of k elements to be开发者_JS百科 proportional to the number k and not to the number of elements stored in the std::vector.

Using pointers, in the general case, I would point to the start of any non continuous region of memory and I would keep account of how many elements it stores. Conceptually, I would fragment the large array into many small ones and not necessarily in continuous space in the memory (the deletion creates "holes" while the allocation does not necessarily "fill" them).

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You achieve this behavior by using std::vector:

std::vector<int> v(6);         // create a vector with six elements.
v.erase(v.begin() + 2);        // erase the element at v[2]
v.insert(v.begin() + 2, 4, 0); // insert four new elements starting at v[2]

Really, any time you want to use a dynamically allocated array, you should first consider using std::vector. It's not the solution to every problem, but along with the rest of the C++ standard library containers it is definitely the solution to most problems.

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You should look into STL containers in C++, for example vector has pretty much the functionality you want.

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I'd advise against doing this on your own. Look up std::vector for a reasonable starting point.

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another option, besides std::vector is std::deque, which works in much the same way, but is a little more efficient at inserting chunks into the middle. If that's still not good enough for you, you might get some mileage using a collection of collections. You'll have to do a little bit more work getting random access to work (perhaps writing a class to wrap the whole thing.