[英]Segmentation fault when running C program
我一直在为CS类中的分配编写C程序,该程序可以成功编译,但是在运行时会出现分段错误错误。 分配处理链表; 我们必须采用描述在头文件linkedlist.h中并声明的方法,并将其实现为文件名为linkedlist.c的文件。 提供了一个名为listtest.c的文件,该文件用于测试该方法。
我的代码(linkedlist.c,注释来自给出的头文件,描述了方法的工作原理):
#include "linkedlist.h"
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
/* Alloc a new node with given data. */
struct ListNode* createNode(int inputData)
{
struct ListNode *newNodeCN;
newNodeCN->data = inputData;
return newNodeCN;
}
/* Insert data at appropriate place in a sorted list, return new list head. */
struct ListNode* insertSorted(struct ListNode* head, int inputData)
{
printf("insertsorted started \n");
struct ListNode * nextIS = NULL;
struct ListNode * newNodeIS = NULL;
struct ListNode * currIS = head;
struct ListNode * listHeadIS = currIS;
if (currIS == NULL)
{
listHeadIS = createNode(inputData);
return listHeadIS;
}
while (currIS->next != NULL)
{
nextIS = currIS->next;
if (currIS->data < inputData)
{
if (nextIS->data >= inputData)
{
nextIS->next = createNode(inputData);
newNodeIS = nextIS->next;
if (newNodeIS->data > listHeadIS->data)
{
listHeadIS = newNodeIS;
}
}
}
currIS = currIS->next;
}
return listHeadIS;
}
/* Remove data from list pointed to by headRef, changing head if necessary.
* Make no assumptions as to whether the list is sorted.
* Memory for removed node should be freed.
* Return 1 if data was present, 0 if not found. */
int removeItem(struct ListNode** headRef, int data)
{
struct ListNode * tempRem = *headRef;
int filterVal = data;
while (tempRem->next != NULL)
{
if (tempRem->data == filterVal)
{
free(tempRem);
tempRem = tempRem->next;
return 1;
}
}
return 0;
}
/* Insert data at head of list, return new list head. */
struct ListNode* push(struct ListNode* head, int data)
{
printf("push started \n");
int dataPush = data;
struct ListNode * tempPush = (struct ListNode*)malloc(sizeof(struct ListNode));
tempPush->data = dataPush;
tempPush->next = head;
*head = *tempPush;
return tempPush;
}
/* Remove and return data from head of non-empty list, changing head.
* Memory for removed node should be freed. */
int pop(struct ListNode** headRef)
{
struct ListNode * tempPop = *headRef;
int tempData;
tempData = tempPop->data;
free(tempPop);
tempPop = tempPop->next;
return tempData;
}
/* Return length of the list. */
int listLength(struct ListNode* head)
{
int i;
while (head->next != NULL)
{
i++;
head = head->next;
}
return i;
}
/* Print list data on single line, separated with spaces. */
void printList(struct ListNode* head)
{
printf("PrintList Started \n");
if (head != NULL)
{
while (head->next != NULL)
{
printf("%d\n", head->data);
head = head->next;
}
}
}
/* Free memory used by the list. */
void freeList(struct ListNode* head)
{
while (head != NULL)
{
free(head);
head = head->next;
}
}
/* Reverse order of elements in the list */
void reverseList(struct ListNode** headRef)
{
struct ListNode * origRL = *headRef;
struct ListNode * nextRL = NULL;
struct ListNode * prevRL = NULL;
while (origRL->next != NULL);
{
nextRL = origRL->next;
prevRL = origRL;
origRL = nextRL;
origRL->next = prevRL;
}
}
来自listtest.c的代码(我没有写这个):
#include <stdio.h>
#include <stdlib.h>
#include "linkedlist.h"
int main(int argc, char** argv)
{
int i, n;
struct ListNode* head = NULL;
struct ListNode* stack = NULL;
printf("empty list: ");
printList(head);
for(i = 0; i < 23; ++i)
{
n = (i*17+11) % 23;
head = insertSorted(head, n);
printf("sort succesful /n");
stack = push(stack, n);
}
printf("filled list: ");
printList(head);
printf("list length = %d\n", listLength(head));
printf("filled stack: ");
printList(stack);
printf("stack size = %d\n", listLength(stack));
for(i = -4; i < 25; i+=4)
{
n = removeItem(&head, i);
if(!n) printf("remove did not find %d\n", i);
}
printf("list after removes: ");
printList(head);
printf("list length = %d\n", listLength(head));
for(i = 0; i < 5; ++i)
{
printf("pop: %d\n", pop(&stack));
}
printf("stack after pops: ");
printList(stack);
printf("stack size = %d\n", listLength(stack));
reverseList(&head);
printf("list after reverse: ");
printList(head);
freeList(head);
head = NULL;
freeList(stack);
stack = NULL;
return 0;
}
根据Valgrind和GDB的说法,分割错误是由主要原因引起的。 Valgrind给我错误:
Access not within mapped region at address 0x6FFFFFFE3
==6300== at 0x400953: main
我的问题是究竟是什么导致分段错误,我该如何解决,代码中的其他任何内容都可能导致分段错误? 我不允许编辑listtest.c,因此任何更改都必须在linkedlist.c中。 谢谢。
struct ListNode * newNodeCN; newNodeCN-> data = inputData; 实际上没有分配新节点
int listLength(struct ListNode * head)-我从未初始化。
oid freeList(struct ListNode * head)-自由,然后取消引用
在insertSorted函数中,条件if(newNodeIS-> data ...)在没有验证其不是NULL的情况下取消对指针的引用,这是分段错误的根源。 尝试修复该报告:)
首先在函数createNode中,u使用元素“ data”,但没有为newNodeCN分配真正的内存,即类型为struct ListNode。 此外,当您要引用错误的内存地址(例如,指针不是malloc或数组外的地址等等)时,通常会出现“分段错误”。
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