Thread: Tree help please..

Hi All,

I make a BinarySearchTree implementation and it reads the a txt with more than 50000 inputs. It compiles perfectly but when I run it.. It gives me segmentation fault error, this program is simple to understand yet the Segmentation Fault error is so confusing since it does not explain what's the error is.. I was thinking there might be something wrong with the pointers, but I have been debugging for more than 2 days now and I couldn't find my error with the pointers.. Would someone explain what I did wrong? Here is my code..

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct BSTree *BST;

struct BSTree {
    int elm;
    BST left;
    BST right;
};

BST initiateTree(BST T) {
    if(T != NULL) {
        initiateTree(T->left);
        initiateTree(T->right);
        free(T);
    }
}

BST insertTree(int a, BST T) {
    if(T == NULL) {    
        T = malloc(sizeof(struct BSTree));
        if(T == NULL) {
            fprintf(stderr, "insert: FATAL - malloc failed!\n");
        } else {
            T->elm = a;
            T->left = T->right = NULL;
        }
    } else {
        if(a < T->elm) {
            T->left = insert(a, T->left);
        } else {
            if(a > T->elm) {
                T->right = insert(a, T->right);
            }
        }
    }
    return T;
}

main() {
    BST T;
    int element;
    FILE *fp;

    T = initiateTree(NULL);
    if((fp = fopen("data_search.txt", "r")) == NULL) {
        printf("main: FATAL - Failed to open data_search.txt!\n");
        return 0;
    } else {
        printf("main: Success to open data_search.txt\n");

        while(!feof(fp)) {
            element = getc(fp);
            insertTree(element, T);
        }
    }
}

Thank you so much..

Hi Salem,

Thank you for your reply.. As you mentioned before, I stored the return of insert() to the struct (T). Also, changed the main() to int main() that returns 0 at the last part.. I also checked and revised my code logic against your seg-fault error checklist, however, I still get the seg-fault error.. Would you explain a little bit more detail what si the error is in this small program? I attached my revised code here..

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct BSTree *BST;

struct BSTree {
	int elm;
	BST left;
	BST right;
};

BST makeEmpty(BST T) {
	if(T != NULL) {
		makeEmpty(T->left);
		makeEmpty(T->right);
		free(T);
	}
}

BST insert(int a, BST T) {
	if(T == NULL) {	
		T = malloc(sizeof(struct BSTree));
		if(T == NULL) {
			fprintf(stderr, "insert: FATAL - malloc failed!\n");
		} else {
			T->elm = a;
			T->left = T->right = NULL;
		}
	} else {
		if(a < T->elm) {
			T->left = insert(a, T->left);
		} else {
			if(a > T->elm) {
				T->right = insert(a, T->right);
			}
		}
	}
	return T;
}

int main() {
	BST T;
	int element, i;
	FILE *fp;
	
	T = makeEmpty(T);
	if((fp = fopen("data_search.txt", "r")) == NULL) {
		printf("main: FATAL - Failed to open data_search.txt!\n");
		return 0;
	} else {
		printf("main: Success to open data_search.txt\n");

		while(!feof(fp)) {
			element = getc(fp);
			T = insert(element, T);
		}
	}
	return 0;
}

Thank you so much..

Hi All,

Thanks for the advice from Brad0407 and iMalc, the intention to have makeEmpty() is to initialize a pointer but it is a bad practice to have a pointer that point to garbage.. So I get rid of it and initialize the pointer in the while(!feof(fp)) {}.. But it still gives me segmentation fault, yet I could not find other logic error(s).. Is there any stupid mistakes that I do in this program? Thank you..

Well, you shouldn't be using feof to control a loop: Cprogramming.com FAQ > Why it's bad to use feof() to control a loop.