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。我是 C 的新手，在分配指针和诸如此类的东西时仍然被抛出一个循环，所以我真的需要一些帮助。
代码如下。文件的顺序是 LinkedLists.h(LinkedList 模块的头文件)、LinkedLists.c(LinkedList 模块)和 TestList.c(主模块)。
/******************************************************************************
* 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_ */
链表.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 %s\n", 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 %s\n", 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: %s\n", 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;
}
程序编译正常。但是，运行它会在执行结束时导致段错误，并且 valgrind 会报告多个内存泄漏(如下所示)。如果您能提供任何帮助，我将不胜感激。问题主要出在 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(我都试过了，但它们的功能几乎相同，但都不起作用)。该 block 是一个 do/while 循环，如下所示:
do
{
CurElement = RemoveFromFrontOfLinkedList(LL);
if(CurElement != NULL)
printf("Word #%d: %s\n", 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)
最佳答案
==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)
这里指的是下面的代码:
LinkedListNodes *removedNode = malloc(sizeof(removedNode));
removedNode = ListPtr->FrontPtr;
您malloc 一 block 内存，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。
正如 Valgrind 所指出的，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，这意味着您丢失了对已分配内存的引用:
CurElement = RemoveFromFrontOfLinkedList(LL);
关于c - C 链表中的内存泄漏，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14069536/