使用 C 中的比较 function 递归地插入二叉搜索树

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

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).

2. You need to define struct City.

3. You need to #include <stdlib.h> for malloc.

4. 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 int t = 15; int g = 13 and later insertInBST(root, &t, &g)

5. In main you use the wrong compare function (doubles instead of int).

6. 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.

7. In insertInBST, you only need to do the comparison once to figure out if you need the left or right branch.