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alter array size in struct?

 
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Ghoti



Joined: 31 Dec 2005
Posts: 288
PostPosted: Fri Sep 01, 2006 6:30 pm    Post subject: alter array size in struct? Reply with quote
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?
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Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php
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memon



Joined: 03 Oct 2005
Posts: 63
PostPosted: Fri Sep 01, 2006 10:20 pm    Post subject: Reply with quote
yes... if you use C++ it is really easy:

Code:
#include <vector>

struct Vertex { float x, y, z; }

...

struct Mesh
{
  std::vector<Vertex> verts;   
};

...

Mesh* m = new Mesh;

int n = ReadNumVertices();
m->verts.resize(n);

for(int i = 0; i < n; ++i)
  m->verts[i] = ReadVertex();


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

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


If you prefer C, you use malloc:

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

Mesh* m = new Mesh;

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

for(int i = 0; i < n; ++i)
  m->verts[i] = ReadVertex();


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:

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

C++

Code:
delete m
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Ghoti



Joined: 31 Dec 2005
Posts: 288
PostPosted: Mon Sep 04, 2006 12:39 am    Post subject: Reply with quote
Thanks that is really helpfull :) thanks again
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Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php
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