[英]Segmentation Fault: 11 - C Linked-List
我試圖在C中實現鏈表。我使用了一種稱為NODE的結構。 出於某些原因,當我調用函數createList()
時會遇到Segmentation Error 11
。 我調試了我的代碼,並且我很確定該錯誤發生在這里:
/* 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);
我認為錯誤是因為未正確分配內存。 但是我為每個節點值初始化了一個50個字符的數組,因此程序不應該自己管理內存嗎?
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為NULL **
雖然我沒有任何分段錯誤,但是我的頭沒有初始化...我正在從文件中讀取輸入,並為文件的每一行創建一個節點。 因此,我正在測試head == NULL並將頭發送給add(struct * NODE)。 那不應該初始化頭嗎?
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,這將是一個問題。
/* 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
通常會導致分段錯誤。
在這種情況下,您始終要分配一個新節點。 嘗試這個:
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;
}
在我看來,人頭沒有分配
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