C语言链表节点创建异常及段错误排查求助

First, let's tackle each of your problems step by step:

Problem 1: Unexpected Node Numbers (Output Shows 1 3 3) #

The root cause here is that you're only allocating memory for one node outside the loop in creation_noeud, then reusing that same pointer for every iteration. This means all "nodes" in your linked list are actually the same block of memory—each loop overwrites the num and u values, and the next pointers end up creating a circular reference (pointing back to the same node). That's why you see repeated 3s.

Fix for Node Numbering #

Move the malloc call inside the loop so you create a brand new node each time:

void creation_noeud(maillages mail){
    int i;
    noeuds new;
    mail->lst_noe = NULL;
    for (i = 0; i < mail->nb_noe; i++){
        // Allocate a new node for each iteration
        new = (noeuds)malloc(sizeof(struct noeud));
        if (!new) { // Always check if malloc succeeded!
            perror("Failed to allocate node");
            exit(EXIT_FAILURE);
        }
        new->num = i + 1;
        printf("Deplacement du noeud %d: ", new->num);
        scanf("%lf", &new->u);
        new->next = mail->lst_noe;
        mail->lst_noe = new;
    }
}

With this fix, your linked list will use the head-insert method correctly—so the first node in the list will be the last one you created (number 3), followed by 2, then 1. Your printf will now output 1 3 2 for the first three parameters.

Problem 2: Segmentation Fault #

There are a few issues causing the segfault—let's fix them one by one:

Issue 1: Mismatched printf Format and Arguments #

In your main function, you have 3 %d placeholders but pass 4 integer arguments:

// Wrong: 3 format specifiers, 4 arguments
printf("aaa %d %d %d aaa \n",1,mail->lst_noe->num,mail->lst_noe->next->num,mail->lst_noe->next->next->num);

This triggers undefined behavior, which can lead to a segfault. Update the format string to match the number of arguments:

printf("aaa %d %d %d %d aaa \n",1,mail->lst_noe->num,mail->lst_noe->next->num,mail->lst_noe->next->next->num);

Issue 2: recherche_noe Corrupts the Original List #

Right now, your recherche_noe function modifies the original list's head pointer (mail->lst_noe) when traversing. This destroys the list structure, leading to broken pointers and segfaults later. Instead, use a temporary pointer to traverse without altering the original list:

noeuds recherche_noe(maillages mail,int num){
    noeuds temp = mail->lst_noe; // Use a temp pointer to traverse
    printf("%d %d ",num, mail->lst_noe->num);
    while(temp != NULL && temp->num != num){
        temp = temp->next;
    }
    return temp; // Returns NULL if not found, the node if found
}

Issue 3: Unchecked Null Pointers #

If you try to access next on a NULL pointer (e.g., if you create fewer than 3 nodes but access lst_noe->next->next), you'll get a segfault. Always add checks before dereferencing pointers:

// In main, check if the list has enough nodes before accessing
if (mail->lst_noe && mail->lst_noe->next && mail->lst_noe->next->next) {
    printf("aaa %d %d %d %d aaa \n",1,mail->lst_noe->num,mail->lst_noe->next->num,mail->lst_noe->next->next->num);
} else {
    printf("Not enough nodes in the list!\n");
}

Bonus: Avoid Memory Leaks #

To clean up allocated memory when your program finishes, add a helper function to free the linked list:

void free_noeuds(noeuds head) {
    noeuds temp;
    while (head != NULL) {
        temp = head;
        head = head->next;
        free(temp);
    }
}
// Call this in main before exiting
free_noeuds(mail->lst_noe);
free(mail);

内容的提问来源于stack exchange，提问作者Talal C.