Односвязный список(С)

[Yokai0]

Обьясниите пожалуйста, как работает этот код. Чем подробнее, тем лучше

func.h

#pragma once
#ifndef FUNC_H
#define FUNC_H
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>

struct SBirthday
{
	int mDay;
	int mMonth;
	int mYear;
};
typedef struct SStudent
{
	char mName[25];
	char mSurname[25];
	struct SBirthday mBirthday;
	int mMarks[6];
	struct SStudent* next, *prev;
} student;

void scanStudent(FILE* f, student* p);
void insertInProperPosition(student** head, student** tail, student* p);
void insertInTheEnd(student** tail, student* p);
void printList(student* head);
int studentCmp(student* a, student* b);
student* deleteStudent(student** head, student** p);

#endif // !FUNC_H

Source.c

#include "func.h"

int main()
{
	int n = 1;
	FILE* fl = fopen("C:\\Users\\oleg\\Desktop\\fl.txt", "r");

	student* head = (student*)malloc(sizeof(student));
	scanStudent(fl, head);
	student* tail = head, *p = NULL;

	while (!feof(fl))
	{
		p = (student*)malloc(sizeof(student));
		scanStudent(fl, p);
		insertInProperPosition(&head, &tail, p);
		n++;
	}

	p = head;
	student* psave = p;
	while (p)
	{
		psave = p->next;
		if (isStudentToDelete(p))
			free(deleteStudent(&head, &p));

		p = psave;
	}

	printList(head);

	_getch();
	return 0;
}

func.c

#include "func.h"

void scanStudent(FILE* fl, student* p)
{
	fscanf(fl, "%s", &p->mSurname);
	fscanf(fl, "%s", &p->mName);
	fscanf(fl, "%d", &p->mBirthday.mDay);
	fscanf(fl, "%d", &p->mBirthday.mMonth);
	fscanf(fl, "%d", &p->mBirthday.mYear);
	for (int i = 0; i < 6; i++)
		fscanf(fl, "%d", &p->mMarks[i]);
	p->next = NULL;
	p->prev = NULL;
}
int isStudentToDelete(student* s)
{
	int del = 0, m[5] = { 0 };
	for (int i = 0; i < 6; i++)
		m[s->mMarks[i] - 1] = 1;

	for (int i = 1; i < 5; i++)
		if (m[i] == 0)
			return 0;

	return 1;
}
void printList(student* head)
{
	student* a = head;
	while (a)
	{
		printf("%s %s\n", a->mSurname, a->mName);
		a = a->next;
	}
}
void insertInProperPosition(student** head, student** tail, student* p)
{
	int inserted = 0;
	if (studentCmp(p, *head) < 0)
	{
		p->next = *head;
		(*head)->prev = p;
		*head = p;
		inserted = 1;
	}

	student* temp = *head;
	while (temp->next && !inserted)
	{
		if (studentCmp(p, temp->next) < 0)
		{
			student* s = temp->next;
			temp->next = p;
			p->next = s;
			s->prev = p;
			p->prev = temp;
			inserted = 1;
		}
		temp = temp->next;
	}


	if (!inserted)
	{
		(*tail)->next = p;
		p->prev = *tail;
		*tail = p;
	}
}
void insertInTheEnd(student** tail, student* p)
{
	(*tail)->next = p;
	p->prev = (*tail);
	(*tail) = p;
}
int studentCmp(student* a, student* b)
{
	if (strcmp(a->mSurname, b->mSurname) < 0)
		return -1;
	if (strcmp(a->mSurname, b->mSurname) > 0)
		return 1;

	// surnames are equal here:
	if (strcmp(a->mName, b->mName) < 0)
		return -1;
	if (strcmp(a->mName, b->mName) > 0)
		return 1;

	return 0;
}
student* deleteStudent(student** head, student** p)
{
	student* toFree = *p;
	if (!((*p)->prev))
	{// p is head
		(*p)->next->prev = NULL;
		*p = (*p)->next;
		*head = *p;
	}
	else if (!((*p)->next))
	{// p is tail
		(*p)->prev->next = (*p)->next;
	}
	else
	{// p is in the middle
		(*p)->prev->next = (*p)->next;
		(*p)->next->prev = (*p)->prev;
	}

	return toFree;
}

Заранее благодарен.