Program do zarządzania studentami

main.c

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

typedef struct student {
  int   uid; // unique identifier
  float gpa; // grade point average
  char *firstname;
  char *lastname;
} student_t;

typedef struct list {
  struct student *stud;
  struct list *next;
} list_t;

list_t* init(student_t *stud) {
  list_t *head = malloc(sizeof(list_t));
  if (head == NULL) {
    fprintf(stderr, "[!] Nie udało się zainicjalizować listy\n");
    return NULL;
  }

  head->stud = stud;
  head->next = NULL;
  return head;
}

size_t length(list_t *head) {
  list_t *last = head;
  size_t n = 0;

  while (last != NULL) {
    n += 1;
    last = last->next;
  }

  return n;
}

int push(list_t *head, student_t *stud) {
  list_t *last = head;
  list_t *tail;

  if (head == NULL) {
    fprintf(stderr, "[!] Niezainicjalizowana lista\n");
    return 1;
  }

  while (last->next != NULL) {
    last = last->next;
  }

  last->next = malloc(sizeof(list_t));
  if (last->next == NULL) {
    fprintf(stderr, "[!] Nie udało się dodać elementu do listy\n");
    return 2;
  }
 
  tail = last->next;
  tail->stud = stud;
  tail->next = NULL;

  return 0; 
}

/* Poprzednia implementacja funkcji
student_t* pop(list_t *head) {
  list_t *last = NULL;
  list_t *tail = head;
  
  if (head == NULL) {
    fprintf(stderr, "[!] Lista jest pusta\n");
    return NULL;
  }

  if (head->next == NULL) {
    fprintf(stderr, "[!] Lista zawiera tylko jeden element\n");
    return NULL;
  }

  while (tail->next != NULL) {
    last = tail;
    tail = tail->next;
  }

  student_t *stud = tail->stud;

  free(tail);

  last->next = NULL;

  if (stud != NULL) {
    printf("[<] (%d) %s %s\n", stud->uid, stud->firstname, stud->lastname);
  } else {
    printf("[<] (nothing)\n");
  }
  return stud;
}
*/

list_t* pop(list_t *head, student_t* output) {
  list_t *tail = head;
  list_t *last = NULL;

  if (head == NULL) {
    fprintf(stderr, "[!] Nie zainicjalizowana lista\n");
    return head;
  }

  while (tail->next != NULL) {
    last = tail;
    tail = tail->next;
  }

  if (output == NULL) {
    fprintf(stderr, "[!] Nie mam gdzie zapisać wyniku\n");
    return head;
  }

  if (tail->stud == NULL) {
    fprintf(stderr, "[!] Brak informacji o studencie\n");
    return head;
  }

  // FIXME: what if tail->stud and output overlap?
  memcpy(output, tail->stud, sizeof(student_t));
  printf("[<] (%d) %s %s\n", output->uid, output->firstname, output->lastname);

  // tail->stud is managed by other function
  free(tail);
  
  if (last != NULL) {
    last->next = NULL;
    return head;
  } else {
    return NULL;
  }
}

void print(list_t *head) {
  list_t *last = head;
  printf("[*] Lista ma %zu elementów\n", length(head));
  while (last != NULL) {
    printf("[%p] stud => %p\n", (void*)last, (void*)last->stud);
    last = last->next;
  }
}

int main(int argc, char **argv) {
  student_t bchaber = {207390, 3.0, "Bartosz", "Chaber"};
  student_t kojak   = {275981, 5.0, "Telly", "Savalas"};
  student_t gal     = {999999, 1.0, "Gal", "Anonim"};

  student_t output  = {0};

  list_t *head = init(&kojak);
  push(head, &gal);
  push(head, &bchaber);
  print(head);
  head = pop(head, &output);
  print(head);
  head = pop(head, &output);
  print(head);
  head = pop(head, &output);
  print(head);
  head = pop(head, &output);
  print(head);
  return 0;
}