converting heap based vector to stack

Question

I would like to convert it to vector of vectors but I'm confused about the code above it's better to store it on stack rather than heap, that's why I want to change it to vector of vector

std::vector<DPoint*>* pixelSpacing; ///< vector of slice pixel spacings
pixelSpacing = new std::vector<DPoint*>(volume.pixelSpacing->size());
for (unsigned int i = 0; i < pixelSpacing->size(); i++)
{
 (*pixelSpacing)[i] = new DPoint(*(*volume.pixelSpacing)[i]);
}

• Quimby: I see no vector of vectors. There is usually no point to store vector itself on the heap, it already stores its elements on the heap anyway, so you are only pushing the three pointers it contains to the heap. Why store DPoint by pointer again? Why not just by value? You should use pointers because you need to manually manage lifetime or refer to objects, no just because they are non-primitive types, this is not Java.
• Thomas Weller: You don't have any deletes for all your news.
• Andre Ahmed: @ThomasWeller that's why I want to remove the new, and make vector of vectors
• Andre Ahmed: @Quimby Can you make an answer with the suggestions, I didn't understand it
• Thomas Weller: Maybe you want std::array

Answer 1

Okay, as per the comment, I am making an answer.

std::vector<DPoint> pixelSpacing(volume.pixelSpacing->size()); 
for (unsigned int i = 0; i < pixelSpacing.size(); i++)
{
 pixelSpacing[i] = DPoint(/*DPoint constructor args*/);
}

Or alternatively:

std::vector<DPoint> pixelSpacing;
//Reserving size is optional.
pixelSpacing.reserve(volume.pixelSpacing->size());
for (unsigned int i = 0; i < volume.pixelSpacing->size(); i++)
{
 pixelSpacing.emplace_back(/*DPoint constructor args*/);
}

Answer 2

An std::vector is allocated on the heap. There's no way to "convert it" so that it allocates stuff on the stack. You may create a new vector-like sequence container that allocates on the stack is one thing you can do. Or you can use std::array which allocates on the stack by default.

• Thomas Weller: The vector can be allocated on the stack. Its elements are allocated in the free store.
• Andre Ahmed: I want to remove the news..
• Andre Ahmed: Can you show me the equivelent of the above code using std::array ?