[SOLVED] (C) How do you store objects on the fly?

Question

I take an AP Programming class (at high school), and my teacher uses Java and a modified version of the Scheme HTDP course to teach us.
I love Python for its simple effectiveness, and I love C for its power.
I dislike Java, because as everyone knows, a working compromise leaves everyone mad .
That said, I just finished my "space invaders" project in Java. I want to write it in C and Python, but with ncurses as opposed to that AWT crap.
The python isn't really a problem, but...
Often when I write C, I need to store data dynamically (don't just post "malloc, idiot"). In C++, the vector object is great way to do this. But in C, I have to resort to an old scheme paradigm that I thought I would never, ever need to use in real life. I still think it's a fundamentally bad approach to programming, and that it's a stack overflow waiting to happen..
Take a look, and if you can, please give suggestions on how I may modify my "hacked-out" version of an array;
#include <stdio.h>
#include <stdlib.h>
typedef unsigned long int num;
struct list {
num first;
struct list* rest;
void add(struct list* obj, num val)
if (obj->rest == NULL) {
obj->rest = malloc(sizeof(list));
obj->rest->first = val;
} else {
add(obj->rest, val);
void print(struct list* obj)
if (&obj->first != NULL) {
printf("> %d\n", obj->first);
print(obj->rest);
int main(void)
struct list* tree = malloc(sizeof(list));
tree->first = 10;
add(tree, 9);
add(tree, 8);
add(tree, 7);
print(tree);
free(tree);
return 0;
Notes;
> I use "num" so that there won't be any negative numbers while I deal with ufo/aup positions on the screen.
> "add()" inserts a "num" to the end of the list.
> "print()" prints out the whole list.
> I am not very comfortable using recursion this way. I don't think it's very safe, I just don't know any better...
This is the output this file produces;
> 10
> 9
> 8
> 7
Last thing (I swear). These are sample functions in my actual vadorz.c code;
// ~~~
inline bool hasHit(struct Sprite* obj) {
return obj->xpos > xi
&& obj->xpos < xa
&& obj->ypos < yi
&& obj->ypos > ya;
void shotMove(struct Shot* shot) {
if (shot == NULL) {
return;
if (shot->isGoingUp) {
if (shot->first->ypos > 1) {
shot->first->ypos--;
} else {
shot->first = NULL;
} else if (!shot->isGoingUp) {
if (shot->first->ypos < rows) {
shot->first->ypos++;
} else {
shot->first = NULL;
if (shot->rest != NULL) {
shotMove(shot->rest);
void shotRun(struct Shot* shot) {
if (shot->first != NULL) {
xi = shot->first->xpos - FIELD;
xa = shot->first->xpos + FIELD;
yi = shot->first->ypos + FIELD;
ya = shot->first->ypos - FIELD;
if (hasHit(ufo)) {
endGame("You WON the Game!");
} else if (hasHit(aup)) {
endGame("Well. You failed.");
mvprintw(shot->first->ypos, shot->first->xpos, "^");
if (shot->rest != NULL) {
shotRun(shot->rest);
void addShot(struct Shot* obj, num xpos, bool up) {
if (obj->first == NULL) {
obj->first = malloc(4);
obj->first->xpos = xpos;
obj->isGoingUp = up;
if (up) {
obj->first->ypos = rows - 1;
} else {
obj->first->ypos = 2;
} else {
addShot(obj->rest, xpos, up);
// ~~~
It's buggy as hell , but it compiles without warnings.
Last edited by vkumar (2008-10-25 19:24:50)

Answer 1

You really need to read a good book on data structures. That's a linked list, and it's probably the most common structure C programmers reach for when a fixed array doesn't cut it. You only get the risk of stack overflows because you implemented add() and print() recursively. Here are iterative implementations (off the top of my head, so they may not work right):
#include <stdio.h>
#include <stdlib.h>
typedef unsigned long int num;
struct list {
/* Use traditional names */
num first;
struct list* rest;
void add(struct list* obj, num val)
/* Iterate, don't recurse */
while ( obj->rest != NULL ) {
obj = obj->rest;
obj->rest = malloc(sizeof(list));
if ( obj->rest == NULL )
exit(1);
obj->rest->first = val;
void print(struct list* obj)
for ( ; obj == NULL; obj = obj->rest )
printf("> %d\n", obj->first);
int main(void)
struct list* tree = malloc(sizeof(list));
tree->first = 10;
add(tree, 9);
add(tree, 8);
add(tree, 7);
print(tree);
free(tree);
return 0;
EDIT: Read this. It should answer any other questions you have.
Last edited by skymt (2008-10-25 15:15:32)