【发布时间】：2013-04-23 18:28:46
【问题描述】：
我添加联系人的程序方法之一是在执行时出现以下错误：
Unhandled exception at 0x00111deb in G00290342.exe: 0xC0000005: Access violation reading location 0x00000050.
我研究了这个错误，发现它是由访问已在使用的内存引起的。我已将其缩小到导致“curr”变量为 NULL 的 readFile 方法中的指针逻辑。
它正在中断的代码在这里：
while(curr->next != NULL)
{
curr = curr->next;
}
这是完整的方法供参考：
int addContact(struct contact *theList)
{
struct contact *newContact, *curr;
char fn[15],sn[15],ph[15],cmpy[15],eml[15];
//create the new structure
newContact = (struct contact *)malloc(sizeof(struct contact));
if(newContact == NULL)
{
return(0);
}
//find the end of list
curr = theList;
//scroll through the list
while(curr->next != NULL)
{
curr = curr->next;
}
//now have the last contact and the new one here
printf("\nEnter a surname: ");
gets(newContact->sname);
printf("\nEnter a first name: ");
gets(newContact->fname);
printf("\nEnter a phone: ");
gets(newContact->phone);
printf("\nEnter a company: ");
gets(newContact->company);
printf("\nEnter an email: ");
gets(newContact->email);
//add the new contact to the end of the list
curr->next = newContact;
newContact->prev = curr;
newContact->next = NULL;
return(0);
}//end addContact
这是我读取测试文件的主要方法：
main()
{
int sts,iChoice;
struct contact *ptrList, *head;
//head of sorted list
struct contact *srtdList;
srtdList = NULL;
ptrList = NULL;
ptrList = readFile("test.csv",ptrList);
head = ptrList;
/////menu for options
system("cls");
printf("\n\n\t\tWelcome to BV Contact Organizer\n\n");
printf("\n\n\t\tEnter a number ranging from 1 to 6 for options.\n\n");
printf("\n\t\t1. Search");
printf("\n\t\t2. Add");
printf("\n\t\t3. Sort");
printf("\n\t\t4. Remove");
printf("\n\t\t5. Edit");
printf("\n\t\t6. Exit");
printf("\n\n\t\tEnter your menu choice: ");
fflush(stdin);
scanf("%d", &iChoice);
// user enters one of 6 values:
// Search,add,sort,remove,exit or edit contacts
switch(iChoice)
{
case 1: // Add
{
sts = addContact(head);
sts = writeListToFile("test.csv",head);
while(ptrList != NULL)
{
printf("\n%s,%s,%s,%s,%s",ptrList->sname,ptrList->fname,ptrList->phone,ptrList->company,ptrList->email);
ptrList = ptrList->next;
}
break;
}
case 2: // Sort
{
//return the head of the sorted list to here
srtdList = sortList(head,srtdList);
head = srtdList;
if(srtdList != NULL)
{
printf("\n\nSorted List");
while(srtdList != NULL)
{
printf("\n%s,%s,%s,%s,%s",srtdList->sname,srtdList->fname,srtdList->phone,srtdList->company,srtdList->email);
srtdList = srtdList->next;
}
sts = writeListToFile("testSort.csv",head);
}
else
{
printf("nothing to print");
}
printf("\n\n\n");
system("pause");
break;
}
case 3: // Exit
{
printf("\n\nProgram exiting!...");
break;
}
default:
{
printf("\n\nInvalid menu choice,please choose a number ranging from 1 to 6!...");
}
}//end of switch
return(iChoice);
} // end of main
这是所要求的结构联系定义：
struct contact {
char sname[15];
char fname[15];
char phone[15];
char company[15];
char email[15];
struct contact *prev;
struct contact *next;
};
这是用于读取文件的方法并导致问题：
struct contact *readFile(char * FName,struct contact *ptrList)
{
struct contact *head, *newContact;
FILE *fptr;
char oneLine[60];
char *sname, *fname, *phone,*company, *email;
head = ptrList;
fptr = fopen(FName,"r");
if(fptr == NULL)
{
printf("\nCant open file!");
return(ptrList);
}
fgets(oneLine, 55, fptr);
while(!feof(fptr))
{
fgets(oneLine, 55, fptr);
if(oneLine[strlen(oneLine)-1] == '\n')
{
oneLine[strlen(oneLine)-1] = '\0';
}
sname = strtok(oneLine,",");
fname = strtok(NULL,",");
phone = strtok(NULL,",");
company = strtok(NULL,",");
email = strtok(NULL,",");
if(head == NULL)
{
head = (struct contact *)malloc(sizeof(struct contact));
ptrList = head;
strcpy(head->sname,sname);
strcpy(head->fname,fname);
strcpy(head->phone,phone);
strcpy(head->company,company);
strcpy(head->email, email);
head->prev = NULL;
head->next = NULL;
}
else
{
newContact = (struct contact *)malloc(sizeof(struct contact));
head->next = newContact;
newContact->prev = head;
newContact->next = NULL;
//copy the data to the new one
strcpy(head->sname,sname);
strcpy(head->fname,fname);
strcpy(head->phone,phone);
strcpy(head->company,company);
strcpy(head->email,email);
//move down the list so that the head variable
//points to the last contact
head = newContact;
}
}//end while
fclose(fptr);
return(ptrList);
}
【问题讨论】：
-
您确定
curr不是NULL，因为它看起来就是这样。看起来与NULL这里的0x00000050有些偏移 -
您没有检查“theList”是否为 NULL。如果是这样，您的 while 循环将失败。至少断言它。
-
您可能想在尝试遍历之前检查
theList是否为NULL，因为如果是，您新分配的节点应该成为新的列表头。此外，由于报告的值不是0x00000000，很可能您一开始就没有正确地将列表头初始化为NULL，这是逻辑上的另一个错误。最后，您需要通过地址（即双指针）传入列表头，或者始终将真实的列表头作为函数结果返回，否则您将永远无法正确设置外部列表头。 -
而且.. 好像这还不够，不要使用
gets()。该功能在安全方面非常糟糕，它已从语言中弃用，并且不会包含在下一个标准中。请改用fgets()。由于您正在更新您的问题帖子，您是否有机会也可以添加struct contact的结构定义？ -
@WhozCraig 我认为是
0x00000050，因为这是next在contact对象中的偏移量。
标签： c pointers memory-management data-structures