在為結構指針執行malloc時出現分段錯誤

Question

我試着寫基本的鏈表代碼。 我有兩個函數將數據添加到列表的開頭和列表的結尾。 每次在開頭添加數據的功能都很好。

我總是在insert_end函數中insert_end分段錯誤。 在對malloc執行malloc之后嘗試訪問temp1指向結構時，我收到錯誤。 但這與我在insert_first函數中所做的insert_first ，但每次都有效。 我試着谷歌搜索並在論壇中嘗試，沒有答案。 請幫忙。

這個鏈接是我確切的問題..但我完全不理解解決方案

C中的分段錯誤與malloc

我在這個街區遇到了錯誤

struct node *temp1,*trav;
    temp1 = (struct node *)malloc(sizeof(struct node));
    trav = (struct node *)malloc(sizeof(struct node));
    if (temp1 != NULL) { //******************Segmentation fault at this line**********
        temp1->data = input;
    }






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

//*******Structure to hold linked list*********//
struct node {
    int data;
    struct node *next;
}*head,*temp;


//***********Function to Display everything**********//

void display(struct node *head) {
    struct node *trav;
    trav= (struct node *)malloc(sizeof(struct node));
    printf("Entering into Display\n");
    if (head == NULL) {
        printf("Oh My God, the list is empty\n");
    }
    else {
        trav = head;
        while (trav != NULL) {
            printf("Value stored in [%p] is [%d]\n",trav,trav->data);
            trav = trav->next;
        }
    }
}


//***********Function to Insert at beginning*********//

struct node *insert_first(struct node *head,int input) {
    temp = (struct node *)malloc(sizeof(struct node));
    temp->data = input;
    printf("\nEntering insert first");
    if (head == NULL) {
        head = temp;
        head->next = NULL;
    }
    else {
        temp->next = head;
        head = temp;
    }
    return head;
}


//**************Function to Insert at End******************//
struct node *insert_last(struct node *head,int input) {
    struct node *temp1,*trav;
    temp1 = (struct node *)malloc(sizeof(struct node));
    trav = (struct node *)malloc(sizeof(struct node));
    if (temp1 != NULL) {
        temp1->data = input;
    }
    else {
        printf("empty");
    }
    printf("\nEntering insert last");
    if (head == NULL) {
        head = temp1;
        head->next = NULL;
    }
    else {
        trav = head;
        while (trav != NULL) {
            trav = trav->next;
        }
        trav->next = temp1;
    }
    return head;
}




//*************Main Fucntion***********//

int main() {
    int choice,value;
    head = NULL;
    while(1) {
        printf("\n******Please Enter your choice****\n1. To insert at beginning\n2. To insert at End\n3. To Insert middle\n4. To delete\n5. To display\n0. To Exit\n");
        scanf("%d",&choice);
        switch(choice){
            case 1:
                printf("Please Enter the value to be added\n");
                scanf("%d",&value);
                head = insert_first(head,value);
                break;
            case 2:
                printf("Please Enter the value to be added\n");
                scanf("%d",&value);
                head = insert_last(head,value);
                break;

            case 5:
                display(head);
                break;
            case 0:
                return 0;
            default:
                printf("Thats a wrong choice\n");
                break;
        }
    }
}

Answer 1

這是有問題的塊。

else {
    trav = head;
    while (trav != NULL) {
        trav = trav->next;
    }
    trav->next = temp1;

當你走出while循環時， trav為NULL 。 這就行了

    trav->next = temp1;

因分段違規而失敗。

將該塊更改為：

else {
    trav = head;
    while (trav->next != NULL) {
        trav = trav->next;
    }
    trav->next = temp1;