Segmentation fault on scanf in C. Doesn't make sense [closed] - c

Question

Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 8 years ago.
Improve this question
I have done this countless times before and for some reason now I cannot seem to scanf a string in C.
Here is my code for the specific function:
int putIn(NODE **head,NODE **current,NODE **prev) {
char tempName[40];
printf("Enter party name: ");
scanf("%s",tempName);
printf("Good?");
current=head;
int match=0;
printf("Hi");
while (*current !=NULL) {
printf("No");
if (strcmp((*current)->name,tempName)==0) {
printf("Name exists already");
match=1;
*current=(*current)->next;
}
}
printf("HI");
The function does not even get to the printf("Good"); statement. thanks for your help!
Edit:
Here is all code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define NODE struct node
struct node {
char name[20];
int number;
NODE *next;
};
int counter;
int putIn(NODE **head,NODE **current,NODE **prev);
int delete(NODE **head,NODE **current,NODE **prev);
int show(NODE **head,NODE **current,NODE **prev);
NODE *head=NULL;
NODE *current=NULL;
NODE *prev=NULL;
char tempName[40];
int main() {
int whileLoop=0;
while(whileLoop==0) {
printf("Enter A Command: (1)Insert Party (2)Delete Party (3)Show List (4)Quit: ");
int selection;
scanf("%d",&selection);
switch(selection) {
case 1:
putIn(&head,&current,&prev);
break;
case 2:
delete(&head,&current,&prev);
break;
case 3:
show(&head,&current,&prev);
break;
case 4:
whileLoop=1;
break;
default:
putIn(&head,&current,&prev);
}
}
return 0;
}
int putIn(NODE **head,NODE **current,NODE **prev) {
//char tempName[40];
printf("Enter party name: ");
scanf("%s",tempName);
printf("Good?");
current=head;
int match=0;
printf("Hi");
while (*current !=NULL) {
printf("No");
if (strcmp((*current)->name,tempName)==0) {
printf("Name exists already");
match=1;
*current=(*current)->next;
}
}
printf("HI");
current=(NODE **)malloc(sizeof(NODE *));
if (*head==NULL) {
head=current;
}
(*current)->next=NULL;
strcpy((*current)->name,tempName);
printf("enter party size: ");
scanf("%d",&(*current)->number);
prev=head;
int i;
for (i=0;i<counter-1;i++){
*prev=(*prev)->next;
}
if (counter!=0) {
(*prev)->next=*current;
}
printf("%d",(*head)->number);
counter+=1;
return 0;
}
int delete(NODE **head,NODE **current,NODE **prev) {
int openTable;
printf("Enter open table size: ");
scanf("%d",&openTable);
current=head;
int match=0;
int grow=0;
while (*current!=NULL) {
if ((*current)->number<=openTable) {
match=1;
printf("A table of %d has been removed",(*current)->number);
prev=head;
int i;
for (i=0;i<grow-1;i++) {
*prev=(*prev)->next;
}
(*prev)->next=(*current)->next;
free(*current);
counter-=1;
} else {
grow+=1;
*current=(*current)->next;
}
}
return 0;
}
int show(NODE **head,NODE **current,NODE **prev) {
if (head==NULL) {
printf("\nNo data entered");
}
else {
printf("\nHere is the waiting list: \n");
}
current=head;
while (*current !=NULL) {
printf("Name: %s Size: %d\n",(*current)->name,(*current)->number);
*current=(*current)->next;
}
return 0;
}

Answer 1

The problem has nothing to do with scanf if you don't enter something too long. Your candidates for crash are:
while (*current != NULL) {
and
if (strcmp((*current)->name, tempName) == 0) {
depending on the initialization status of your pointers to pointers, one of these might lead to segfault.
You have to provide the context of the function call where you call putIn(...);
Edit: After you gave insight into your logic, here's the error:
You start out with:
NODE *head = NULL;
NODE *current = NULL;
NODE *prev = NULL;
and, without any further initialization, go into:
putIn(&head, &current, &prev);
where you do the following:
...
current = (NODE **)malloc(sizeof(NODE *));
...
which means, the actual parameter (an important address value, that has been copied on the stack) in the function call is overwritten by the malloc result (which can't be correct, maybe you meant *current = (NODE *) malloc(sizeof(NODE)); ... or sth. else).
In the next step, you initialize (disconnect too) head with the already-disconnected current:
if (*head == NULL) {
head = current;
}
In the next line, you dereference the allocated pointer and access it as it would point to a structure node (with a NODE* member), which has not been allocated so far ...
(*current)->next = NULL;
which segfaults (because *current does not point to an allocated structure node).