c - PrintList function is not working properly -
i'm working on list program course , seems working correctly far, thing acting weird printlist function. let's compile program , push 1 number (e.g. 4) in first node , print list, output is: [4]->[0]->null if didn't add node 0 data. sorry in advance if stupid question, here code wrote:
#include <stdio.h> #include <stdlib.h> struct node{ int data; struct node *next; }; typedef struct node node; void printlist(node *); void push(node **, int ); void insert(node *, int ); void append(node **, int ); void delete(node **, int ); void reverse(node **); int main(){ node *head, *temp; head=malloc(sizeof(node *)); if(head==null){ puts("cannot allocate memory"); } int i, t; int x; while(1){ printf("insert choice:\n1. print list\n2. push\n3. insert\n4. append\n5. delete\n6. reverse\n\nenter other number exit."); scanf("%d", &x); switch(x){ case 1: printlist(head); break; case 2: printf("\ninsert data push: "); scanf("%d", &i); push(&head, i); printlist(head); break; case 3: printf("\ninsert data insert: "); scanf("%d", &i); printf("\ninsert data of previous node: "); scanf("%d", &t); temp=head; while(temp->data!=t){ temp=temp->next; } insert(temp, i); printlist(head); break; case 4: printf("\ninsert data append: "); scanf("%d", &i); append(&head, i); printlist(head); break; case 5: printf("\ninsert value of node delete: "); scanf("%d", &i); delete(&head, i); printlist(head); break; case 6: reverse(&head); break; default: printf("\nexiting program."); exit(1); break; } } return 0; } void printlist(node *n){ while(n!=null){ printf("[%d]->", n->data); n=n->next; } printf("null\n\n"); return; } void push(node **headptr, int d){ node *newnode; newnode=malloc(sizeof(node *)); if(newnode==null){ puts("\ncannot allocate memory\n"); } newnode->next=(*headptr); newnode->data=d; (*headptr)=newnode; return; } void insert(node *prev, int d){ node *newnode; newnode=malloc(sizeof(node *)); if(newnode==null){ puts("\ncannot allocate memory\n"); } newnode->next=prev->next; newnode->data=d; prev->next=newnode; return; } void append(node **headptr, int d){ node *newnode, *cursor; newnode=malloc(sizeof(node *)); if(newnode==null){ puts("\ncannot allocate memory\n"); } newnode->next=null; newnode->data=d; if((*headptr)==null){ (*headptr)=newnode; return; } else{ cursor=(*headptr); while(cursor->next!=null){ cursor=cursor->next; } cursor->next=newnode; return; } } void delete(node **headptr, int d){ if((*headptr)==null){ puts("list empty"); return; } else{ node *temp=null, *cursor; cursor=(*headptr); while(cursor->data!=d){ temp=cursor; cursor=cursor->next; } temp->next=cursor->next; free(cursor); return; } } void reverse(node **headptr){ if((*headptr)==null){ puts("list empty"); return; } else{ node *prev=null, *current=(*headptr), *next; while(current!=null){ next=current->next; current->next=prev; prev=current; current=next; } (*headptr)=prev; return; } } edit: feel free give me suggestion code.
two problems
the first 1 pointed @bluepixy, reserving space wrong size:
malloc(sizeof(node *)); /* size of pointer object */ should be
malloc(sizeof(node)) /* size of object */ and in first call push() assigning address of uninitialized pointer:
newnode->next=(*headptr); /* (*headptr) contains garbage @ point */
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