Help with structures and recursion

[highsummonerbob]

I'm making this ai program, but I'm having some trouble. I've made a smaller program that shows what what's wrong.

#include <stdio.h>

struct test *tree(struct test *p);

struct test {
  int t;
  struct test *test2;
};

int j=0;

int main() 
{
  
  struct test *root;
  
  
  tree(root);
  
  printf("Roots t %d \n",root->t);
  
}


struct test *tree(struct test *p) 
{
  struct test *malloc();
  
  *p = *malloc(sizeof(struct test));
      printf("Hi\n");
  
  p->t=1;
  if(j==0){
    j++;
    tree(p->test2);
      printf("Test2's t %d\n", p->test2->t);
      
    }
  
    return(p);
}

So the main function calls tree, sending root as an argument. It is malloced space for the structure, t is set to 0, then it calls itself with a pointer in root to an instance of itself. It's t is assigned a 1, then it is supposed to be returned, print that it is eaual to 1, then return to the main function and say that its equal to 1. However, it gets a segmentation fault the first time it trys to print p->test2->t.

[quzah]

 struct test *malloc();

What are you doing? Don't reprototype malloc.

*p = *malloc(sizeof(struct test));

Wrong two ways.

1) You should be passing a pointer to a pointer if you plan on actually updating the pointer outside of your test or tree function. (IE: Making it point to something not allocated.)

2) You shouldn't be dereferencing malloc.

struct foo *myfun( struct **foo )
{
    *foo = malloc( sizeof (struct foo) );
    ...do stuff...
}

...do stuff...

struct foo *thisonehere;

myfun( &thisonehere );

Next, you never actually test the return value of malloc. That's wrong. Additionally, you're using a global, which there is no need for. But that should get you started.

Quzah.

[highsummonerbob]

I know that I'm not testing malloc, but I didn't include error checking in this program just to make it simpler. I also don't usually use global variables, but in this case, it was easier to have a global variable rather than passing the function two arguments. I haven't tried your suggestions yet but I will do so soon.