Question

I have a pointer array of a custom Vector typedef (just 3 floats). I’m writing a Wavefront object loader and I want to be able to add to an array of these vectors whenever a vertex row in the file is encountered. My problem at the moment is allocating memory for the new vector.

Vector

typedef struct
{
    float x;
    float y;
    float z;
}
Vector;

Parsing the line and saving in memory

Vector *verticies;

Vector tmp;
verticies = new Vector;

long endPtr = sizeof(verticies);

sscanf(line, "v %f %f %f", &verticies[endPtr].x, &verticies[endPtr].y, &verticies[endPtr].z);

return;

There are eight vertices in the .obj file and the output of sizeof(verticies) shows 8 all the time. The problem with the code above is that the new vertex is given to the last element in *verticies, so my question is; ** how do I add elements to the end of a pointer array dynamically?**

Answer 1

You are allocating space for exactly one Vector struct.

sizeof(vertices) will be the size of a pointer on your machine and is absolutely meaningless here.

sscanf(line, "v %f %f %f", &(verticies->x), &(verticies->y), &(verticies->z));

is going to do what you need. But this only enabling you to read in a single Vector.
You either need to allocate enough space (as many vectors as you have lines) and use a for loop to match the line with the offset in the array.

But you really should be using std::vector and a std::ofstream.