From: "Philip Bock" <bockfam AT icenter DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Arrays of pointers...
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Message-ID: <TEDS3.1137$1J5.105718@typhoon.mbnet.mb.ca>
Date: Sat, 30 Oct 1999 14:54:43 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

What I'm trying to do is create a vector graphics renderer. So I have vector
images stored as structs (called vimg), with an array of pointers to the
shapes that make up the vector drawings (called shape). But it seems that
the compiler doesn't go for the idea that I want to designate an array in a
struct without defining it's size, so I tried just defining it as a pointer,
trusting my constructor to deal with the assignment. But when the
constructor assigns the pointer a value that points to another pointer (e.g.
the beginning of the array) I get error messages. How do I fix?

Errors:
vector.cpp: In method `shape::shape(int, int, int)':
vector.cpp:139: assignment to `vector *' from `vector **'
vector.cpp: In method `vimg::vimg(int, int, int *)':
vector.cpp:147: assignment to `shape *' from `shape **'
vector.cpp:149: no match for `shape & = shape *'
vector.cpp:24: candidates are: struct shape & shape::operator =(const
shape&)

Code:
#include <allegro.h>
#include <iostream.h>
#include <conio.h>
#include <stdlib.h>

struct coord
{
 int x, y;
};

struct vector
{
 coord c1, c2;
 int color;
};

struct shape
{
 int numvects;
 int stype;
 int sfill;
 vector *vects;
 shape(int newnumvects, int newstype, int newsfill);
};

struct vimg
{
 int numvectors, numshapes;
 vector *vectors;
 shape *shapes;
 vimg(int nnumv, int nnums, int vpers[]);
};

void program_init(void);
void draw_vimg(vimg vectimg);
vimg *gen_vimg(void);
shape::shape(int newnumvects, int newstype, int newsfill);
vimg::vimg(int nnumv, int nnums);

int main(void)
{
// program_init();
// set_gfx_mode(GFX_VESA1, 640, 480, 0, 0);

 vimg *mygraphic;
 mygraphic = gen_vimg();
// draw_vimg(mygraphic);

// set_gfx_mode(GFX_TEXT, 0, 0, 0, 0);
}

void program_init(void)
{
 clrscr();
 gotoxy(37, 1);
 cout << "Atest1\n";

 cout << "Initializing Allegro library...\n";
 allegro_init();

 cout << "Setting up timer...\n";
 install_timer();

 cout << "Initializing mouse routines...";
 if (install_mouse() == -1)
  cout << "failed\n";
 else
  cout << '\n';
 cout << "Detected Operating System: ";

 if (os_type == OSTYPE_UNKNOWN)
  cout << "MS-DOS\n";
 if (os_type == OSTYPE_WIN95)
  cout << "Windows 95\n";
 if (os_type == OSTYPE_DOSEMU)
  cout << "Linux DOSEMU\n";
}

void draw_vimg(vimg vectimg, int x, int y, int xscale, int yscale)
{
 for(int a = 0; a != vectimg.numshapes; a++)
 {
  file://Code to draw one shape's outline
  for(int b = 0; b != vectimg.shapes[a].numvects; b++)
   line(screen, (vectimg.shapes[a].vects[b].c1.x*xscale)+x,
(vectimg.shapes[a].vects[b].c1.y*yscale)+y,
(vectimg.shapes[a].vects[b].c2.x*xscale)+x,
(vectimg.shapes[a].vects[b].c2.y*yscale)+y,
vectimg.shapes[a].vects[b].color);
  // Code to fill shape goes here.
 }
}

vimg *gen_vimg(void)
{
 int vpers[]={6};
 vimg newvimg(6, 1, vpers);

 newvimg.vectors[0].c1.x = 50;
 newvimg.vectors[0].c1.y = 1;
 newvimg.vectors[0].c2.x = 100;
 newvimg.vectors[0].c2.y = 1;
 newvimg.vectors[0].color = 1;
 newvimg.vectors[1].c1.x = 100;
 newvimg.vectors[1].c1.y = 1;
 newvimg.vectors[1].c2.x = 150;
 newvimg.vectors[1].c2.y = 50;
 newvimg.vectors[1].color = 1;
 newvimg.vectors[2].c1.x = 150;
 newvimg.vectors[2].c1.y = 50;
 newvimg.vectors[2].c2.x = 100;
 newvimg.vectors[2].c2.y = 100;
 newvimg.vectors[2].color = 1;
 newvimg.vectors[3].c1.x = 100;
 newvimg.vectors[3].c1.y = 100;
 newvimg.vectors[3].c2.x = 50;
 newvimg.vectors[3].c2.y = 100;
 newvimg.vectors[3].color = 1;
 newvimg.vectors[4].c1.x = 50;
 newvimg.vectors[4].c1.y = 100;
 newvimg.vectors[4].c2.x = 1;
 newvimg.vectors[4].c2.y = 50;
 newvimg.vectors[4].color = 1;
 newvimg.vectors[5].c1.x = 1;
 newvimg.vectors[5].c1.y = 50;
 newvimg.vectors[5].c2.x = 50;
 newvimg.vectors[5].c2.y = 1;
 newvimg.vectors[5].color = 1;

 newvimg.shapes[0].vects[0] = newvimg.vectors[0];
 newvimg.shapes[0].vects[1] = newvimg.vectors[1];
 newvimg.shapes[0].vects[2] = newvimg.vectors[2];
 newvimg.shapes[0].vects[3] = newvimg.vectors[3];
 newvimg.shapes[0].vects[4] = newvimg.vectors[4];
 newvimg.shapes[0].vects[5] = newvimg.vectors[5];
}

shape::shape(int newnumvects, int newstype, int newsfill)
{
 numvects = newnumvects;
 stype = newstype;
 sfill = newsfill;
 vects = new vector *[newnumvects];
}

vimg::vimg(int nnumv, int nnums, int vpers[])
{
 numvectors = nnumv;
 numshapes = nnums;
 vectors = new vector [nnumv];
 shapes = new shape *[nnums];
 for (int c = 0; c != nnums; c++)
  shapes[c] = new shape(vpers[c], 0, 0);
}