alter array size in struct?

[Ghoti]

Hi folks,

Since i only know C and i do not know C++, i'm trying to make an .obj loader in c using a struct as some form of class. The problem however is that i do not know how to fill up an array of vertices inside a struct (change the number of the array), is it possible to initialize the array when you know the number of vertices you want to store?

[memon]

yes... if you use C++ it is really easy:

Code: Select all

#include <vector>

struct Vertex &#123; float x, y, z; &#125;

...

struct Mesh
&#123;
  std&#58;&#58;vector<Vertex> verts;    
&#125;;

...

Mesh* m = new Mesh;

int n = ReadNumVertices&#40;&#41;;
m->verts.resize&#40;n&#41;;

for&#40;int i = 0; i < n; ++i&#41;
  m->verts&#91;i&#93; = ReadVertex&#40;&#41;;

And If you need to pass the array to some function, which prefers a pointer to Vertex, it goes like this:

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void DrawVertexArrayThing(const Vertex* verts, int n);
...
DrawVertexArrayThink(&m->verts[0], m->verts.size());

If you prefer C, you use malloc:

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struct Mesh
{
  Vertex* verts;
  in nverts;
};

Mesh* m = new Mesh;

int n = ReadNumVertices();
m->verts = (Vertex*)malloc(n * sizeof(Vertex));
m->nverts = n;

for&#40;int i = 0; i < n; ++i&#41;
  m->verts&#91;i&#93; = ReadVertex&#40;&#41;;

The std::vector will free the memory for you when you destroy the mesh, but with the C method, you will need to free the mesh yourself:

C:

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free(m->verts);
free(m);

C++

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delete m

[Ghoti]

Thanks that is really helpfull :) thanks again