有人可以告诉我我的函数添加到链接列表的逻辑是否正确？

Question

我启动了一个函数来将结构添加到链接列表中。我的教授希望我们按姓氏和名字的字母顺序添加结构。我最近对链接列表感到非常困惑，所以我想知道是否有人可以告诉我我是否使用了正确的逻辑或完全搞砸了。

// Similar to hw06, you will be inserting into a list of students sorted by their last name.
// Similar to hw05, there may be students on the list that have the same last name.
// You will also be tested to assure that a student is not added to the list twice (same first name and last name).
// If a student already exists with the same last name, then you will need to sort them by their first names.
//
// If the student is already on the list, return the integer value 0.
// If the student is not on the list, add the student to the list and return the integer value 1.
//
// "list" is initialized as NULL. Use this as your 'head' of the list and insert into it accordingly.
// There are 4 possibilities for inserting into the list:
//  - inserting into an empty list
//  - inserting at the beginning of the list
//  - inserting inbetween 2 nodes in the list
//  - inserting at the end of the list
int add(struct student* new_student)
{
struct container* temp = list;
// Nothing is in the list yet
if(temp == NULL){
    temp->student = new_student;
    temp->next = NULL;
    list->next = temp;
    return 1;
}
else{

    // If the list is not empty
    while(temp->next != NULL){

        // If a last name in the list is the same as the last name of the new student
        if(strcmp(temp->student->lastName, new_student->lastName) == 0){

            // If the first name is the same
            if(strcmp(temp->student->firstName, new_student->firstName) == 0){
                return 0;
            }
            // If the first name is different
            else{
                // Sort by first name instead of last name
            }
        }
    }
}


}

Answer 1

我在 if block 中发现了几个问题。

// Nothing is in the list yet
if(temp == NULL) {

   // This is a problem
   // You enter this block when temp is NULL.
   // Setting temp->new_student and temp->next when temp is NULL
   // causes undefined behavior.
   temp->student = new_student;
   temp->next = NULL;

   // This is a problem
   // You enter this block when list is NULL.
   // Setting list->next when list is NULL causes undefined behavior.
   list->next = temp;

   return 1;
}

您需要的是:

if(temp == NULL) {
   // Allocate memory for a new container.
   // Set the member data
   temp = malloc(sizeof(*temp));
   temp->student = new_student;
   temp->next = NULL;
   list = temp;
   return 1;
}