使用strtok函数时程序崩溃【C语言】

Hey Marco, let's break down why your program is crashing and get your tokenization + linked list task working smoothly. From what you've shared, here are the most likely culprits and fixes:

1. The #1 Cause of strtok() Crashes: Modifying Read-Only Strings #

strtok() works by replacing delimiters in the input string with \0 to split tokens. If you pass a string literal (like char *input = "your input here";) to strtok(), you're trying to write to read-only memory (where string literals are stored). This will immediately crash your program.

Fix: #

Always use a modifiable character array for your input:

// Bad: String literal (read-only)
// char *input = "apple banana cherry date";

// Good: Modifiable array
char input[1024];
printf("Enter your string: ");
fgets(input, sizeof(input), stdin);
// Optional: Trim the newline from fgets
input[strcspn(input, "\n")] = '\0';

2. Linked List Memory Management Mistakes #

Crashes often happen here if you skip critical steps:

• Forgetting to check if malloc() succeeded (returns NULL if out of memory)
• Not initializing node pointers properly (leading to dereferencing NULL)
• Mishandling the linked list head/tail pointers during insertion

Example of Safe Node Creation & Insertion #

Here's how to safely add even-positioned tokens to your linked list and track occurrences:

struct node* createNode(const char* token) {
    struct node* newNode = (struct node*)malloc(sizeof(struct node));
    if (!newNode) {
        perror("malloc failed");
        exit(EXIT_FAILURE);
    }
    strncpy(newNode->sbuffer, token, Dim - 1);
    newNode->sbuffer[Dim - 1] = '\0'; // Ensure null termination
    newNode->occ = 1;
    newNode->next = NULL;
    return newNode;
}

// Add token to list (or increment count if it exists)
void addToken(struct node** head, const char* token) {
    struct node* current = *head;
    // Check if token already exists
    while (current != NULL) {
        if (strcmp(current->sbuffer, token) == 0) {
            current->occ++;
            return;
        }
        current = current->next;
    }
    // Token doesn't exist, add new node to head (or tail, your choice)
    struct node* newNode = createNode(token);
    newNode->next = *head;
    *head = newNode;
}

3. Correctly Tracking Even-Positioned Tokens #

Make sure your position counter is initialized correctly. Remember:

• If you count starting at 1 (1st token = position 1, 2nd = position 2, etc.), even positions are 2,4,6...
• If you start at 0, even positions are 0,2,4...

Example Tokenization Loop #

struct node* head = NULL;
char* token = strtok(input, " "); // Split on spaces (adjust delimiters as needed)
int position = 1; // Start counting at 1

while (token != NULL) {
    if (position % 2 == 0) { // Check for even position
        addToken(&head, token);
    }
    token = strtok(NULL, " "); // Get next token
    position++;
}

4. Printing the Linked List Safely #

Don't forget to handle an empty list, and always traverse with a temporary pointer to avoid losing the head:

void printList(struct node* head) {
    if (!head) {
        printf("No even-positioned tokens found.\n");
        return;
    }
    printf("Even-positioned tokens and their counts:\n");
    struct node* current = head;
    while (current != NULL) {
        printf("'%s': %d times\n", current->sbuffer, current->occ);
        current = current->next;
    }
}

Final Notes #

• Always free the linked list memory when you're done to avoid leaks:

void freeList(struct node** head) {
    struct node* temp;
    while (*head != NULL) {
        temp = *head;
        *head = (*head)->next;
        free(temp);
    }
}

• Double-check that your delimiter set in strtok() matches your needs (e.g., include commas, tabs if required).

内容的提问来源于stack exchange，提问作者Marco Follo