Insert in Binary search tree recursively using comparison function in C - c

Question

I am using nested structures to create a BST but I have a problem while inserting because I use a comparison function to do so!
here is my comparison function
int compare_doubles(const void* a, const void* b)
{
const double* a_ = (const double*)a;
const double* b_ = (const double*)b;
return (*a_ > *b_) - (*a_ < *b_);
}
int compare_int(const void* a, const void* b)
{
const int* a_ = (const int*)a;
const int* b_ = (const int*)b;
return (*a_ > *b_) - (*a_ < *b_);
}
and here is the structures
typedef struct tree_t BinarySearchTree; //opaque structure declared on BinarySearchTree.h
struct tree_t{
int (*comparison)(const void *, const void *);
struct tree_t* lchild;
struct tree_t* rchild;
struct t_node* noeud;
};
struct t_node{
const void *key;
const void *data;
City *city;
};
and this is my function to create a new BST
BinarySearchTree* newBST(int comparison_fn_t(const void *, const void *))
{
BinarySearchTree *t = (struct tree_t *)malloc(sizeof(struct tree_t));
t->comparison = comparison_fn_t;
t->lchild = t->rchild = NULL;
t->noeud = NULL;
return t;
}
This is my insertion function
BinarySearchTree* insertInBST(BinarySearchTree* bst, const void* key, const void* value) {
BinarySearchTree *t = bst;
if (bst->noeud == NULL)
{
struct t_node* n = (struct t_node *)malloc(sizeof(struct t_node));
t->noeud = n;
t->noeud->data = value;
t->noeud->key = key;
return t;
}
if ((bst->comparison(&key,&(bst->noeud->key))) < 0){
bst->lchild = insertInBST(bst->lchild, key, value);
}
else if ((bst->comparison(&key,&(bst->noeud->key))) >= 0){ // handle duplicate keys
bst->rchild = insertInBST(bst->rchild, key, value);
}
return bst;
}
when I try to run my code using these tests I get segfault (core dumped)
this is my main function
int main()
{
int *t =15;
int *g = 13;
int *j =15;
int *k = 13;
BinarySearchTree *root = newBST(&compare_doubles);
insertInBST(root, k,j);
insertInBST(root, t, g);
}```

Answer 1

Your comparison function is overly complicated (*a_ > *b_) - (*a_ < *b_) as you mix comparison (<, >) and arithmetic (-) operations. #WhozCraig suggested (a < b) ? -1 : (b < a).
You need to define struct City.
You need to #include <stdlib.h> for malloc.
In main you are casting integers to pointers. The compiler warning for the first case is:
warning: initialization of ‘int *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
As in int t = 15; int g = 13 and later insertInBST(root, &t, &g)
In main you use the wrong compare function (doubles instead of int).
I ran your code through gdb and it crashes in if (bst->noeud == 0) because insertInBST(root, t, g) invokes bst->rchild = insertInBST(bst->rchild, key, value) but bst->rchild is NULL.
In insertInBST, you only need to do the comparison once to figure out if you need the left or right branch.