我一直在为学校做一个项目(今晚到期！(，我有一些严重的内存问题。我对C还很陌生，当涉及到对指针进行mallocating之类的操作时，我仍然会被抛出一个循环，所以我真的需要一些帮助。
代码如下。文件的顺序是LinkedLists.h(LinkedList模块的Header(、LinkedLists.c(LinkedListmodule(和TestList.c(Main module(。
/******************************************************************************
* Base struct to contain data structure element information: deterimined by
* the application needs.
******************************************************************************/
#ifndef _LINKED_LISTS_H_
#define _LINKED_LISTS_H_
typedef struct ElementStructs
{
int ElementPosition;
char* ElementValue;
} ElementStructs;
/************** Nothing else in the module needs to be modified *************/
/******************************************************************************
* Base struct of list nodes, contains user information and link pointers.
* The "ElementStructs" typemark must be defined based on specific needs of the
* application.
******************************************************************************/
typedef struct LinkedListNodes
{
/* The user information field */
ElementStructs *ElementPtr;
/* Link pointers */
struct LinkedListNodes *Next;
struct LinkedListNodes *Previous;
} LinkedListNodes;
/******************************************************************************
* Base struct used to manage the linked list data structure.
******************************************************************************/
typedef struct LinkedLists
{
/* Number of elements in the list */
int NumElements;
/* Pointer to the front of the list of elements, possibly NULL */
struct LinkedListNodes *FrontPtr;
/* Pointer to the end of the list of elements, possibly NULL */
struct LinkedListNodes *BackPtr;
} LinkedLists;
/******************************************************************************
* Initialized the linked list data structure
******************************************************************************/
void InitLinkedList(LinkedLists *ListPtr);
/******************************************************************************
* Adds a record to the front of the list.
******************************************************************************/
void AddToFrontOfLinkedList(LinkedLists *ListPtr, ElementStructs *DataPtr);
/******************************************************************************
* Adds a record to the back of the list.
******************************************************************************/
void AddToBackOfLinkedList(LinkedLists *ListPtr, ElementStructs *DataPtr);
/******************************************************************************
* Removes (and returns) a record from the front of the list ('works' even on
* an empty list by returning NULL).
******************************************************************************/
ElementStructs *RemoveFromFrontOfLinkedList(LinkedLists *ListPtr);
/******************************************************************************
* Removes (and returns) a record from the back of the list ('works' even on
* an empty list by returning NULL).
******************************************************************************/
ElementStructs *RemoveFromBackOfLinkedList(LinkedLists *ListPtr);
/******************************************************************************
* De-allocates the linked list and resets the struct fields as if the
* list was empty.
******************************************************************************/
void DestroyLinkedList(LinkedLists *ListPtr);
#endif /* _LINKED_LISTS_H_ */
LinkedLists.c:
/******************************************************************************
* Extracts and prints the first and last 6 elements from the specified data
* set and prints the total number of words in the input file. Utilizes the
* LinkedList module as specified in LinkedLists.h
* Written by xxxxxxx
******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include "LinkedLists.h"
void InitLinkedList(LinkedLists *ListPtr)
{
ListPtr->NumElements = 0;
ListPtr->FrontPtr = NULL;
ListPtr->BackPtr = NULL;
}
void AddToFrontOfLinkedList(LinkedLists *ListPtr, ElementStructs
*DataPtr)
{
/* If there are no other elements, create new node and add it,
* assigning it to both the front and back pointers */
if(ListPtr->NumElements == 0)
{
ListPtr->FrontPtr = malloc(sizeof(LinkedListNodes));
ListPtr->FrontPtr->ElementPtr = DataPtr;
ListPtr->FrontPtr->Next = NULL;
ListPtr->FrontPtr->Previous = NULL;
ListPtr->BackPtr = ListPtr->FrontPtr;
}
/* If there are other elements, create new node and add it to the front
* while retaining previous node order */
else
{
/* Initialize new LinkedListNode */
ListPtr->FrontPtr->Previous = malloc(sizeof(LinkedListNodes));
ListPtr->FrontPtr->Previous->ElementPtr = DataPtr;
ListPtr->FrontPtr->Previous->Next = ListPtr->FrontPtr;
ListPtr->FrontPtr->Previous->Previous = NULL;
/* Assign newly initialized node as front node of LinkedList */
ListPtr->FrontPtr = ListPtr->FrontPtr->Previous;
}
/* List size plus one */
(ListPtr->NumElements)++;
}
void AddToBackOfLinkedList(LinkedLists *ListPtr, ElementStructs
*DataPtr)
{
/* If there are no other elements, create new node and add it,
* assigning it to both the front and back pointers */
if(ListPtr->NumElements == 0)
{
ListPtr->FrontPtr = malloc(sizeof(LinkedListNodes));
ListPtr->FrontPtr->ElementPtr = DataPtr;
ListPtr->FrontPtr->Next = NULL;
ListPtr->FrontPtr->Previous = NULL;
ListPtr->BackPtr = ListPtr->FrontPtr;
/*printf("Adding %sn", DataPtr->ElementValue);*/
}
/* If there are other elements, create new node and add it to the back
* while retaining previous node order */
else
{
/* Initialize new LinkedListNode */
ListPtr->BackPtr->Next = malloc(sizeof(LinkedListNodes));
ListPtr->BackPtr->Next->ElementPtr = DataPtr;
ListPtr->BackPtr->Next->Previous = ListPtr->BackPtr;
ListPtr->BackPtr->Next->Previous = ListPtr->BackPtr;
ListPtr->BackPtr->Next->Next = NULL;
/* Assign newly initialized node as back node of LinkedList */
ListPtr->BackPtr = ListPtr->BackPtr->Next;
printf("Adding %sn", ListPtr->BackPtr->ElementPtr->ElementValue);
}
/* List size plus one */
(ListPtr->NumElements)++;
}
ElementStructs *RemoveFromFrontOfLinkedList(LinkedLists *ListPtr)
{
if(ListPtr->NumElements > 0)
{
ElementStructs *removedElement = ListPtr->FrontPtr->ElementPtr;
LinkedListNodes *removedNode = ListPtr->FrontPtr;
if(ListPtr->NumElements == 1)
{
ListPtr->FrontPtr = NULL;
}
else
{
ListPtr->FrontPtr = ListPtr->FrontPtr->Next;
ListPtr->FrontPtr->Previous = NULL;
}
(ListPtr->NumElements)--;
free(removedNode);
return removedElement;
}
else
{
ElementStructs *nullElement = NULL;
return nullElement;
}
}
ElementStructs *RemoveFromBackOfLinkedList(LinkedLists *ListPtr)
{
if(ListPtr->NumElements > 1)
{
ElementStructs *removedElement = ListPtr->BackPtr->ElementPtr;
LinkedListNodes *removedNode = ListPtr->BackPtr;
if(ListPtr->NumElements == 1)
{
ListPtr->BackPtr = NULL;
}
else
{
ListPtr->BackPtr = ListPtr->BackPtr->Previous;
ListPtr->BackPtr->Next = NULL;
}
(ListPtr->NumElements)--;
free(removedNode);
return removedElement;
}
else
{
ElementStructs *nullElement = NULL;
return nullElement;
}
}
void DestroyLinkedList(LinkedLists *ListPtr)
{
while(ListPtr->FrontPtr != NULL)
{
LinkedListNodes *removedNode = ListPtr->FrontPtr;
ListPtr->FrontPtr = ListPtr->FrontPtr->Next;
/* Deallocate element in node */
free(removedNode->ElementPtr->ElementValue);
free(removedNode->ElementPtr);
/* Deallocate node */
free(removedNode);
}
free(ListPtr);
}
测试列表.c:
/******************************************************************************
* Tests the functionality of the LinkedList specified in LinkedLists.h using
* the file "american-english-words". Reads in individual words and stores them
* as node elements in the LinkedList.
* Written by xxxxx
*****************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "LinkedLists.h"
#define MAX_LENGTH 100 /* Length of longest word in any major English dictionary */
int main(int argc, char** args)
{
if(argc == 2)
{
/* Initialize LinkedList */
LinkedLists *LL;
/* File pointer to input file */
FILE *fp;
/* Node to store input data from file */
ElementStructs *NodeData;
/* Loop completion boolean */
int Done;
/* Loop position counter */
int Position;
/* Iterator */
ElementStructs *CurElement;
/* Open input file and check that it is readable. If not, exit */
fp = fopen(args[1], "r");
if(fp == NULL)
{
fprintf(stderr, "File open failed.");
return 2;
}
/* Initialize linked list and other necessary variables */
LL = malloc(sizeof(*LL));
InitLinkedList(LL);
Done = 0;
Position = 0;
do
{
if(!feof(fp))
{
/* Allocate space for new node data */
NodeData = malloc(sizeof(ElementStructs));
/* Allocate space in node element for input string */
NodeData->ElementValue = malloc(MAX_LENGTH * sizeof(char));
/* Read new node data from file */
fscanf(fp, "%s", NodeData->ElementValue);
/* Assign scanned values to node elements */
NodeData->ElementPosition = Position;
/*strcpy(NodeData->ElementValue, readString);*/
/* Add data node to LinkedList */
AddToFrontOfLinkedList(LL, NodeData);
}
else
Done = 1;
Position++;
}while(Done == 0);
do
{
CurElement = RemoveFromFrontOfLinkedList(LL);
if(CurElement != NULL)
printf("Word #%d: %sn", CurElement->ElementPosition,
CurElement->ElementValue);
}while(CurElement != NULL);
/* Deallocate linked list */
DestroyLinkedList(LL);
fclose(fp);
}
/* Bad command line input */
else
{
fprintf(stderr, "Incorrect number of arguments");
return 1;
}
return 0;
}
这个程序编译得很好。然而，运行它会在执行结束时导致seg故障，valgrind报告多个内存泄漏(如下所示(。如果你能提供任何帮助，我将不胜感激。该问题主要出现在LinkedList.c模块中的RemoveFromBackOfLinkedList和RemoveFromFrontOfLinkedList方法中。主模块(TestList.c(中有一段代码调用其中一个函数(我试过这两个函数，但它们的功能几乎相同，都不起作用(。该块是一个do/while循环，如下所示：
do
{
CurElement = RemoveFromFrontOfLinkedList(LL);
if(CurElement != NULL)
printf("Word #%d: %sn", CurElement->ElementPosition,
CurElement->ElementValue);
}while(CurElement != NULL);
Valgrind结果：
Word #225921: stoich
.
.
.
.
Word #6: Cam's
Word #5: petrochemistry's
Word #4: Tera
Word #3: benedictions
Word #2: wisted
Word #1: toxins
==4849== Invalid write of size 8
==4849== at 0x400B5C: RemoveFromFrontOfLinkedList (in /home/amb2189/hw3/TestList)
==4849== by 0x40085B: main (in /home/amb2189/hw3/TestList)
==4849== Address 0x10 is not stack'd, malloc'd or (recently) free'd
==4849==
==4849==
==4849== Process terminating with default action of signal 11 (SIGSEGV)
==4849== Access not within mapped region at address 0x10
==4849== at 0x400B5C: RemoveFromFrontOfLinkedList (in /home/amb2189/hw3/TestList)
==4849== by 0x40085B: main (in /home/amb2189/hw3/TestList)
==4849== If you believe this happened as a result of a stack
==4849== overflow in your program's main thread (unlikely but
==4849== possible), you can try to increase the size of the
==4849== main thread stack using the --main-stacksize= flag.
==4849== The main thread stack size used in this run was 8388608.
==4849==
==4849== HEAP SUMMARY:
==4849== in use at exit: 23,965,172 bytes in 413,185 blocks
==4849== total heap usage: 619,775 allocs, 206,590 frees, 28,923,332 bytes allocated
==4849==
==4849== 16 bytes in 1 blocks are possibly lost in loss record 1 of 9
==4849== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4849== by 0x4007E2: main (in /home/amb2189/hw3/TestList)
==4849==
==4849== 200 bytes in 2 blocks are possibly lost in loss record 5 of 9
==4849== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4849== by 0x4007F0: main (in /home/amb2189/hw3/TestList)
==4849==
==4849== 23,963,992 (3,305,392 direct, 20,658,600 indirect) bytes in 206,587 blocks are definitely lost in loss record 9 of 9
==4849== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4849== by 0x4007E2: main (in /home/amb2189/hw3/TestList)
==4849==
==4849== LEAK SUMMARY:
==4849== definitely lost: 3,305,392 bytes in 206,587 blocks
==4849== indirectly lost: 20,658,600 bytes in 206,586 blocks
==4849== possibly lost: 216 bytes in 3 blocks
==4849== still reachable: 964 bytes in 9 blocks
==4849== suppressed: 0 bytes in 0 blocks
==4849== Reachable blocks (those to which a pointer was found) are not shown.
==4849== To see them, rerun with: --leak-check=full --show-reachable=yes
==4849==
==4849== For counts of detected and suppressed errors, rerun with: -v
==4849== Use --track-origins=yes to see where uninitialised values come from
==4849== ERROR SUMMARY: 5 errors from 5 contexts (suppressed: 2 from 2)
Segmentation fault (core dumped)
==4769== 8 bytes in 1 blocks are definitely lost in loss record 1 of 4
==4769== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4769== by 0x400B46: RemoveFromFrontOfLinkedList (in /home/amb2189/hw3/TestList)
==4769== by 0x400869: main (in /home/amb2189/hw3/TestList)
这是指以下代码：
LinkedListNodes *removedNode = malloc(sizeof(removedNode));
removedNode = ListPtr->FrontPtr;
malloc一个内存块，然后将其分配给removedNode，然后立即覆盖指针值。这不会分配给removedNode的内容，但会覆盖指针。
Valgrind:指出，下一次内存泄漏发生在main中
CurElement = malloc(sizeof(*CurElement));
CurElement的下一次使用会立即覆盖指针值，这意味着您已经丢失了对分配内存的引用：
CurElement = RemoveFromFrontOfLinkedList(LL);
对您的2个删除函数进行一些更改，
ElementStructs *RemoveFromFrontOfLinkedList(LinkedLists *ListPtr)
{
if(ListPtr->NumElements > 0)
{
/* ElementStructs *removedElement = ListPtr->FrontPtr->ElementPtr;*/
/*LinkedListNodes *removedNode = malloc(sizeof(removedNode)); // no need allocate because you are deleting the node
removedNode = ListPtr->FrontPtr;*/
LinkedListNodes *removedNode = ListPtr->FrontPtr; // use this line
ListPtr->FrontPtr = ListPtr->FrontPtr->Next;
ListPtr->FrontPtr->Previous = NULL;
free(removedNode);
(ListPtr->NumElements)--;
return NULL;
}
else
{
ElementStructs *nullElement = NULL;
return nullElement;
}
}
ElementStructs *RemoveFromBackOfLinkedList(LinkedLists *ListPtr)
{
if(ListPtr->NumElements != 0)
{
ElementStructs *removedElement = ListPtr->BackPtr->ElementPtr;
LinkedListNodes *removedNode = ListPtr->BackPtr;
ListPtr->BackPtr = ListPtr->BackPtr->Previous;
ListPtr->BackPtr->Next = NULL;
free(removedNode);
(ListPtr->NumElements)--; // add this line
return removedElement;
}
else
{
ElementStructs *nullElement = NULL;
return nullElement;
}
}
编辑1
CurElement = malloc(sizeof(*CurElement));这是main中的另一个内存泄漏，您不必使用malloc，只需删除这一行即可。
第2版：为什么不释放ELEMENT和ELEMENTVALUE。。。？
do
{
CurElement = RemoveFromFrontOfLinkedList(LL);
if(CurElement != NULL) {
printf("Word #%d: %sn", CurElement->ElementPosition,
CurElement->ElementValue);
free(CurElement->ElementValue); //add these 2 line to free ELEMENTVALUE And ELEMENT.
free(CurElement);
}
}while(CurElement != NULL);
我认为一个泄漏来自CurElement = malloc(sizeof(*CurElement));。下一次使用CurElement会重写此指针。
目前还不清楚NodeData->ElementValue在哪里被释放。
你想用做什么
LinkedListNodes *removedNode = malloc(sizeof(removedNode));
removedNode = ListPtr->FrontPtr;
您分配了一些空间并覆盖了指针