Question

I am generating a collection of values each frame and I would like to add those values to a larger collection of values at a specific index.

This is a typical example of a collection I am generating

std::vector<glm::vec3> corners;
corners.reserve(8);
//glm::vec3 corners[8];
//std::list<glm::vec3> corners;

corners[i++] = position - hX + hY + hZ;
corners[i++] = position + hX + hY + hZ;
corners[i++] = position + hX - hY + hZ;
corners[i++] = position - hX - hY + hZ;
corners[i++] = position - hX + hY - hZ;
corners[i++] = position + hX + hY - hZ;
corners[i++] = position + hX - hY - hZ;
corners[i++] = position - hX - hY - hZ;

I then have a larger collection of glm::vec3 values that I would like to copy the values above to at a particular index.

std::vector<glm::vec3> vertices;
vertices.assign(maxVertices, 0);

The C# equivalent would be

corners.CopyTo(vertices, index);

What class type can I use to efficiently generate and copy the smaller collection across to the larger one without too much overhead of generating it each frame?

I could get away with assigning each newly generated smaller collection to the end of the larger collection so the index value could be ignored.

Answer 1

In your code you should corners.resize(8), not corners.reserve(8).
Besides, if i understand you correctly, it seems you have always 8 corners?
Use array then:

typedef std::array<glm::vec3, 8> Corners; 
// or in pre-c++0B code use boost::array same way
// or if neither is available then just raw glm::vec3[8] can do.

Then filling can be done with initialization:

// somehow we have position, hX, hY and hZ
Corners corners =
{
    position - hX + hY + hZ,
    position + hX + hY + hZ,
    position + hX - hY + hZ,
    position - hX - hY + hZ,
    position - hX + hY - hZ,
    position + hX + hY - hZ,
    position + hX - hY - hZ,
    position - hX - hY - hZ
};

Copying can be done with standard copy:

std::vector<glm::vec3> vertices;
// somehow it gets filled

// somewhere comes index

std::copy( corners.begin(), corners.end(), vertices.begin() + index );
// with raw glm::vec3[8] std::copy( corners, corners + 8, vertices.begin() + index );

If you need to insert instead of copy then use vertices.insert()