I often use references to simplify the appearance of code:

vec3f& vertex = _vertices[index];

// Calculate the vertex position
vertex[0] = startx + col * colWidth;
vertex[1] = starty + row * rowWidth;
vertex[2] = 0.0f;

Will compilers recognize and optimize this so it is essentially the following?

_vertices[index][0] = startx + col * colWidth;
_vertices[index][1] = starty + row * rowWidth;
_vertices[index][2] = 0.0f;