Thread: delete part of allocated array

The situation is like this:
I know what the max number of the dimension of my data structure will be. But in the case, that the actual space needed is less than max, I would like to delete the unused space.

So, I was thinking something like this, but it won't work

Code:

#include <iostream>
using namespace std;

class foo{
    public:
        foo(){x=0;y=0;z=0;d=0;}
    double x;
    double y;
    double z;
    double d;
};

int main()
{
    foo* p;
    p = new foo[8];
    for(int i = 0 ; i < 8 ; i++)
        cout << i << " " << p[i].x << " " << p[i].y << " " <<  p[i].z << " " << p[i].d << endl;
    foo* pp = &p[5];
    delete [] pp;
    
    return 0;
}

Of course, I made this code only to test this idea.

Any approaches/ new ideas are welcome.

Why don't you use a std::vector?

use vector and resize

you cannot call delete on pointer that was not allocated by new

Maybe because I wrote C lately and did not have vector in mind. That will do the trick. But, is vector behaving as an array? What I want to say, does it store its data in adjacent memory cells?

Then, it is obvious I should go for the vector. But, instead of resizing, what would be best?
Set a vector with the max dimension and then resize once.
Set a vector with no dimension and just push_back data.

Then, it is obvious I should go for the vector. But, instead of resizing, what would be best?
Set a vector with the max dimension and then resize once.
Set a vector with no dimension and just push_back data.

O_o

I agree with whiteflags, because you should always exploit as much information as you have available, but you should also be aware that `std::vector<???>:ush_back' is amortized constant time complexity.

Basically, the internal growth during a `std::vector<???>:ush_back' operation is such that most `std::vector<???>:ush_back' operations do not allocate memory or copy elements around.

[Edit]
O_o

Is it weird that I hate emoticons?
[/Edit]

Soma

Try using [noparse]std::vector<???>::push_back[/noparse].
Don't let them smilies outsmart you.

O_o

I always forget about "NOPARSE" and just didn't know about that the advanced editor had such an option.

Thank you both.

Soma

Or you can just write it like:
std::vector<???>:[I][/I]push_back

Both methods will work. push_back already did.
I want to know the pros and cons. What will be more efficient?

Also, when we write

Code:

myvector.at(i)

we accessing immediately the i-th element, like in an array, or do we have to traverse the vector, like we would do with a linked list?

Originally Posted by std10093

I want to know the pros and cons. What will be more efficient?

Test using representative sample data and find out.

Originally Posted by std10093

we accessing immediately the i-th element, like in an array, or do we have to traverse the vector, like we would do with a linked list?

A std::vector is basically a dynamic array container.