How to correctly initialize C struct array

Question

my problem is that i don't have an idea on how to properly initialize an array containing blocks to drawn on a small matrix display. Initializing the first object works sometimes (block) but going through the for-loop to initialize remaining objects doesn't seem to do anything. I would be very glad for any help!

Structs:

#define MAX_POINTS 50
#define ARRAYSIZE 2

typedef enum {false, true} bool;

typedef struct tpoint {
uint8_t x;
uint8_t y;
} POINT;

typedef struct tGeometery {
int numpoints;
int sizex;
int sizey;
POINT px[ MAX_POINTS ];
} GEOMETRY, *PGEOMETRY;

typedef struct tObj {
    PGEOMETRY geo;
    int dirx,diry;
    int posx,posy;
    void (* draw_object ) (struct tObj *, bool draw);
    void (* move_object ) (struct tObj *);
    void (* set_object_speed ) (struct tObj *, int, int);
} OBJECT, *POBJECT;

"Objects":

GEOMETRY ball_geometry = {
    12,     //Numpoints
    4,4,    //size X,Y
    {
              {1,0},{2,0},
        {0,1},{1,1},{2,1},{3,1},
        {0,2},{1,2},{2,2},{3,2},
              {1,3},{2,3}
    }
};

OBJECT ball = {
    &ball_geometry,
    0,0,    //Direction
    10,1,   //Start position
    draw_object,
    move_object,
    set_object_speed
};

GEOMETRY slab_geometry = {
    30,     //Numpoints
    10,3,   //Size X,Y
    {
        {0,0},{1,0},{2,0},{3,0},{4,0},{5,0},{6,0},{7,0},{8,0},{9,0},
        {0,1},{1,1},{2,1},{3,1},{4,1},{5,1},{6,1},{7,1},{8,1},{9,1},
        {0,2},{1,2},{2,2},{3,2},{4,2},{5,2},{6,2},{7,2},{8,2},{9,2}
    }
};

OBJECT slab = {
    &slab_geometry,
    0,0,    //Direction
    59,61,  //Start position (128/2 - 5)
    draw_object,
    move_object,
    set_object_speed
};

GEOMETRY block_geometry = {
    4,      //Numpoints
    2,2,    //Size X,Y
    {
        {0,0},{1,0},
        {1,0},{1,1}
    }
};

OBJECT block = {
    &block_geometry,
    0,0,    //Direction
    0,0,    //Start position
    draw_object,
    move_object,
    set_object_speed
};

Main:

void main(void) {
graphic_init();
keypad_init();

POBJECT bouncer = &ball;
POBJECT paddle = &slab;
POBJECT targetArray[ARRAYSIZE];
targetArray[0] = &block;

for (int i = 1; i < ARRAYSIZE; i++) {
    targetArray[i] = &block;
    targetArray[i]->posx = targetArray[i-1]->posx+3;
}

bouncer->set_object_speed(bouncer,4,1);
paddle->draw_object(paddle,true);
for (int i = 0; i < ARRAYSIZE; i++) {
    targetArray[i]->draw_object(targetArray[i],true);
}

while(1) {
    bouncer->move_object(bouncer);
}

}

"`typedef enum {false, true} bool;`" Why? C has supported real `bool`s since 1999. Just do `#include `. — Joseph Sible-Reinstate Monica, Jul 12 '20 at 16:26
`void main(void)` This is unnecessarily nonportable. Use `int main(void)` instead. See [What should main() return in C and C++?](https://stackoverflow.com/a/207992) for more details. (And again, since C99, you've been allowed to omit `return 0;` from `main` even though it returns an `int`.) — Joseph Sible-Reinstate Monica, Jul 12 '20 at 16:29

bruno · Accepted Answer · 2020-07-12T19:10:44.587

Doing

POBJECT targetArray[ARRAYSIZE];
targetArray[0] = &block;

for (int i = 1; i < ARRAYSIZE; i++) {
  targetArray[i] = &block;
  targetArray[i]->posx = targetArray[i-1]->posx+3;
}

all the elements of targetArray are the same ( e.g. block ), this not what you want because to do

targetArray[i]->posx = targetArray[i-1]->posx+3;

does in fact the same as :

 targetArray[0]->posx = targetArray[0]->posx+3;

which does finally :

 block.posx = block.posx+3;

and

for (int i = 0; i < ARRAYSIZE; i++) {
  targetArray[i]->draw_object(targetArray[i],true);
}

does the same as :

 for (int i = 0; i < ARRAYSIZE; i++) {
   targetArray[0]->draw_object(targetArray[0],true);
 }

which does finally :

 for (int i = 0; i < ARRAYSIZE; i++) {
   block.draw_object(&block,true);
 }

Why are you doing

POBJECT targetArray[ARRAYSIZE];

rather than

OBJECT targetArray[ARRAYSIZE];

and in tObj

PGEOMETRY geo;

rather than

GEOMETRY geo;

?

Using POBJECT and PGEOMETRY you need a new element for each entry of targetArray and for each field geo, like

targetArray[0] = malloc(sizeof(*(targetArray[0])));
*(targetArray[0]) = block;
targetArray[0]->geo = malloc(sizeof(*(targetArray[0]->geo)));
*(targetArray[0]->geo) = *(block.geo);
for (int i = 1; i < ARRAYSIZE; i++) {
  targetArray[i] = malloc(sizeof(*(targetArray[i])));
  *(targetArray[i]) = block;
  targetArray[i]->geo = malloc(sizeof(*(targetArray[i]->geo)));
  *(targetArray[i]->geo) = *(block.geo);
  targetArray[i]->posx = targetArray[i-1]->posx+3;
}

But using OBJECT and GEOMETRY :

targetArray[0] = block;
for (int i = 1; i < ARRAYSIZE; i++) {
  targetArray[i] = block;
  targetArray[i].posx = targetArray[i-1].posx+3;
}

It is a bad idea to hide a pointer through a typedef, I encourage you to never do that to let the * visible.

I do not also understand why you do

POBJECT bouncer = &ball;
POBJECT paddle = &slab;

rather than to use ball and slab in main

Also main return an int, not void

How to correctly initialize C struct array

1 Answers1