指针显然无缘无故更改 - C

Question

我有一个学校作业，要用 C 创建一个各种各样的数据库，我可以在其中从文件或键盘读取，但数据库本身存储在内存中。

现在，我不会直接就作业寻求帮助，但由于我是 C 新手，我不明白为什么我编写的这段代码不起作用。

源文件的一部分，应该将一个学生添加到链表中。

想在此处添加这些，我将初始值设置为 NULL。

---

struct student *student_root = NULL;
struct teacher *teacher_root = NULL;

    void add_student(char *name) {
    if (student_root == NULL) { //if there is no student in the list

        /* Allocate memory equivalent to the size of struct student
        and store the address in student_root */
        student_root = malloc(sizeof(struct student));
        // ^ this is something I tried to do to fix it, but I think it is not needed

        struct student new; //creating the student root
        inn_student(&new); //innitializing the root
        student_root = &new;
        set_sn(student_root, 1);//sn = student number, like an ID
        set_student_name(student_root, name);

        student_out(*student_root);this works here
    }
    else {
        struct student new; //creating the student that is to be added
        inn_student(&new); //innitializing the student that is to be added

        set_student_name(&new, name);

        printf("%d\n", student_root->student_number);//when I do this, I get a random number instead of '1'
        set_next_student(student_root, &new); // adding the new student to the list (student number is added automatically)
    }
}

我面临的问题是我第一次插入时，student_root 指针正在工作，它指向“新”学生结构。 . .但是当我添加其他东西时，它不起作用。函数完成后，“新”结构是否会被遗忘在内存中？如果是这样，如何解决？

Answer 1

student_root = malloc(sizeof(struct student));

struct student new; //creating the student root
inn_student(&new); //innitializing the root
student_root = &new;

在您初始化student_root 以指向一个堆位置后，接下来几行您再次将其设置为指向一个自动局部变量，当您从该函数返回时，该变量的内存将被其他代码重写。

正确的做法是初始化inn_student(student_root)的字段，而不是inn_student(&new)。