链表使用qsort函数排序，关于cmp函数的问题

函数cmp为什么注释部分换掉1，2不起作用？


#include 
#include 
typedef struct node* list;
struct node {
    int data;
    list next;
};


int cmp(const void* a,const void* b) {
    list p = *(list*)a;
    list *q = (list)b;//1
    return p->data - (*q)->data;//2
    /*list q = *(list*)a;
    return p->data - q->data;*/
}
list sort(list L) {
    int i, n = length(L);
    list  p = L;
    list(*a) = (list)malloc(n * sizeof(struct node));

    i = 0;
    while (p = p->next) {
        a[i] = p;
        i++;
    }

    qsort(a, n, sizeof(list), cmp);

    p = L;
    for (int i = 0; i < n; i++) {
        p->next = a[i];
        p = p->next;
    }
    p->next = NULL;

    return L;
}

//完整代码
#include 
#include 
typedef struct node* list;
struct node {
    int data;
    list next;
};
list creat() {
    list p;
    p = (list)malloc(sizeof(struct node));
    p->next = NULL;
    return p;
}
list insert(list L, int data) {
    list p;
    p = (list)malloc(sizeof(struct node));
    p->data = data;
    p->next = L->next;
    L->next = p;
    return L;
}
int length(list L) {
    list p = L;
    int count = 0;
    while (p = p->next)    count++;
    return count;
}
int cmp(const void* a,const void* b) {
    list p = *(list*)a;
    list *q = (list)b;
    return p->data - (*q)->data;
    /*list q = *(list*)a;
    return p->data - q->data;*/
}
list sort(list L) {
    int i, n = length(L);
    list  p = L;
    list(*a) = (list)malloc(n * sizeof(struct node));

    i = 0;
    while (p = p->next) {
        a[i] = p;
        i++;
    }

    qsort(a, n, sizeof(list), cmp);

    p = L;
    for (int i = 0; i < n; i++) {
        p->next = a[i];
        p = p->next;
    }
    p->next = NULL;

    return L;
}
void print(list L) {
    list p = L;
    while (p = p->next) {
        printf("%d ", p->data);
    }
    printf("\n");
}
int main() {
    list L = creat();
    int n;
    scanf_s("%d", &n);
    for (int i = 0; i < n; i++) {
        insert(L, rand() % n);
    }
    //print(L);
    L = sort(L);
    //print(L);
    return 0;
}


list *q = (list*)b;