[英]Segmentation Fault: 11 - C Linked-List
我试图在C中实现链表。我使用了一种称为NODE的结构。 出于某些原因,当我调用函数createList()
时会遇到Segmentation Error 11
。 我调试了我的代码,并且我很确定该错误发生在这里:
/* Write into node */
strcpy(head->username, cur_username);
strcpy(head->password, cur_pw);
strcpy(head->type, cur_type);
printf("%s %s %s\n", head->username, head->password, head->type);
我认为错误是因为未正确分配内存。 但是我为每个节点值初始化了一个50个字符的数组,因此程序不应该自己管理内存吗?
char *filename = "password.csv";
int n_users = 0;
struct NODE {
char username[50];
char password[50];
char type[50];
struct NODE *next;
} *head=NULL, *curr=NULL;
/* Global placeholders so they can be used by other both add() and creatList() */
char line[50], *cur_username, *cur_pw, *cur_type;
char linecopy[50];
void createList(void) {
printf("Creating list\n");
bool success;
/* Open the file in read-only and copy content into array */
/* File pointer */
FILE *f;
/* Node pointer */
struct NODE * ptr = (struct NODE*) malloc(sizeof(struct NODE));
if (NULL == ptr) {
printf("\nError: was unable to initialize password validation information!! \n");
return;
}
head = curr = ptr;
/* Open the file in read */
f = fopen("password.csv", "r");
/* if f == NULL, there was an error - the file probably does not exist. We don't care, we will create the file later */
if (f != NULL) {
/* Read the file line by line */
while(fgets(line, 49, f) != NULL) {
struct NODE * p = (struct NODE*) malloc(sizeof(struct NODE));
/* Copy line into linecopy because strtok is destructive */
strcpy(linecopy, line);
/* Extract the ids from linecopy */
cur_username = strtok(linecopy, ",");;
cur_pw = strtok(NULL, ",");
cur_type = strtok(NULL, ",");
if(head==NULL)
add(head);
else
add(p);
if (!success) {
printf("\nError: was unable to initialize password validation information!! \n");
return;
}
}
}
/* Close file */
fclose(f);
}
** HEAD为NULL **
虽然我没有任何分段错误,但是我的头没有初始化...我正在从文件中读取输入,并为文件的每一行创建一个节点。 因此,我正在测试head == NULL并将头发送给add(struct * NODE)。 那不应该初始化头吗?
struct NODE {
char username[50];
char password[50];
char type[50];
struct NODE *next;
} *head=NULL, *curr=NULL;
/* Global placeholders so they can be used by other both add() and creatList() */
char line[50], *cur_username, *cur_pw, *cur_type;
char linecopy[50];
void createList(void) {
printf("Creating list\n");
bool success;
/* Open the file in read-only and copy content into array */
/* File pointer */
FILE *f;
/* Node pointer */
struct NODE * ptr = (struct NODE*) malloc(sizeof(struct NODE));
if (NULL == ptr) {
printf("\nError: was unable to initialize password validation information!! \n");
return;
}
head = curr = ptr;
/* Open the file in read */
f = fopen("password.csv", "r");
/* if f == NULL, there was an error - the file probably does not exist. We don't care, we will create the file later */
if (f != NULL) {
/* Read the file line by line */
while(fgets(line, 49, f) != NULL) {
struct NODE * p = (struct NODE*) malloc(sizeof(struct NODE));
/* Copy line into linecopy because strtok is destructive */
strcpy(linecopy, line);
/* Extract the ids from linecopy */
cur_username = strtok(linecopy, ",");;
cur_pw = strtok(NULL, ",");
cur_type = strtok(NULL, ",");
if (head == NULL)
success = add(head);
else
success = add(p);
if (!success) {
printf("\nError: was unable to initialize password validation information!! \n");
return;
}
}
}
/* Close file */
fclose(f);
}
是的,这将是一个问题。
/* Is list empty? */
if (head == NULL) {
/* Write into node */
strcpy(head->username, cur_username);
strcpy(head->password, cur_pw);
strcpy(head->type, cur_type);
printf("%s %s %s\n", head->username, head->password, head->type);
}
取消引用NULL
通常会导致分段错误。
在这种情况下,您始终要分配一个新节点。 尝试这个:
struct NODE *node = malloc(sizeof(struct NODE));
if (node != NULL)
{
strcpy(node->username, cur_username);
strcpy(node->password, cur_pw);
strcpy(node->type, cur_type);
/* push node onto list head */
node->next = head;
head = node;
}
在我看来,人头没有分配
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