在链表中打印节点时无限循环

Question

If I call createnode(x) in main and then follow that with printNodes(); I will get an infinite while-loop that seems to be printing some memory address. I am guessing the issue lies in the fact that i set head = temp?

SinglyLinkedList *head = NULL;

void createNode(int data){
    SinglyLinkedList *temp = malloc(sizeof(SinglyLinkedList));
    temp-> data = data;

    if(head == NULL){
        head = temp;
        return;
    }

    temp->next = head;
    head = temp;
}

void printNodes(){

    SinglyLinkedList *temp = head;

    while ( temp != NULL ){
        printf("%d\r\n",temp->data);
        temp = temp->next;
    }

}

Answer 1

SinglyLinkedList *temp = malloc(sizeof(SinglyLinkedList));
temp->data = data;

if(head == NULL){
    head = temp;
    return;
}

temp->next = head;
head = temp;

should be

SinglyLinkedList *temp = malloc(sizeof(SinglyLinkedList));
temp->data = data;
temp->next = head;    // Moved

if(head == NULL){
    head = temp;
    return;
}

head = temp;

which is a very complicate way of writing

SinglyLinkedList *temp = malloc(sizeof(SinglyLinkedList));
temp->data = data;
temp->next = head;
head = temp;

Without this fix, printNodes results in undefined behaviour as a result of the lack of initialization of temp->next .

Answer 2

I don't see anything wrong with this code. I copied your code and tried calling the createNode function followed by printNodes() and it gave me the correct output.

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

typedef struct x {
    int data;
    struct x* next;
}SinglyLinkedList;


SinglyLinkedList *head = NULL;

void createNode(int data){
    SinglyLinkedList *temp = malloc(sizeof(SinglyLinkedList));
    temp-> data = data;

    if(head == NULL){
        head = temp;
        return;
    }

    temp->next = head;
    head = temp;
}

void printNodes(){

    SinglyLinkedList *temp = head;

    while ( temp != NULL ){
        printf("%d\r\n",temp->data);
        temp = temp->next;
    }

}

int main() {
    createNode(7);
    printNodes();
    return 0;
}

Output: 7
I don't know why you're getting an infinite loop. A suggestion would be to also set temp->next = NULL in your createNode function after temp->data = data