I have two structs declared in this way:
struct record {
const char *entry;
struct record *next;
};
struct s_table {
int capacity;
struct record *records;
};
And I wrote a method to remove a member of the struct s_table:
int s_table_remove_record(struct s_table *t, const char *begin,
const char *end) {
if (!t) {
printf("No table");
return 0;
}
printf("inside remove_record \n");
if (strcmp(begin, t->records->entry) == 0) {
printf("record found in the first if.");
struct record *temp = t->records->next;
free(t);
return 1;
}
printf("Before allocating the head\n");
struct record *head = t->records;
for (; t->records->next; t->records = t->records->next) {
printf("Inside the for loop \n");
if (strcmp(begin, t->records->entry) == 0) {
printf("record found in the second if");
struct record *temp = t->records->next;
t->records->next = t->records->next->next;
free(temp);
return 1;
}
}
printf("record not found\n");
return 0;
}
However I never get inside the for loop. Could you help me understand why and provide a solution?
To test the code:
#include <assert.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct record {
const char *entry;
struct record *next;
};
struct s_table {
int capacity;
struct record *records;
};
static int counter = 0;
struct s_table *s_table_new() {
struct s_table *t = (struct s_table *)malloc(sizeof(t));
t->capacity = 1000;
t->records = (struct record *)malloc(sizeof(struct record) * t->capacity);
return t;
}
int s_table_add_record(struct s_table *t, const char *begin, const char *end) {
if (!t) {
printf("No table");
return 0;
}
if (counter > t->capacity) {
printf("Not enough space!");
return 0;
}
t->records[counter].entry = begin;
printf("Record add is: %s \n", t->records[counter].entry);
if (!t) {
printf("Failed to allocate new recrd");
return 0;
}
return 1;
}
int main() {
static const char *tomatoes = "tomatoes 10Kg CHF 55";
static const char *carrots = "carrots 15Kg CHF 40";
static const char *peppers = "peppers 2Kg CHF 6";
struct s_table *t = s_table_new();
assert(t);
s_table_delete(t);
struct s_table *t2 = s_table_new();
assert(t2);
t = s_table_new();
assert(t);
s_table_delete(t2);
s_table_add_record(t, carrots, carrots + strlen(carrots));
printf("First record added\n");
s_table_add_record(t, carrots, carrots + strlen(carrots));
printf("Second record added \n");
s_table_add_record(t, carrots, carrots + strlen(carrots));
s_table_add_record(t, carrots, carrots + strlen(carrots));
s_table_add_record(t, peppers, peppers + strlen(peppers));
s_table_add_record(t, tomatoes, tomatoes + strlen(tomatoes));
printf("All records added \n");
s_table_remove_record(t, peppers, peppers + strlen(peppers));
return 1;
}
Related
I'm facing the segmentation fault error in the following dynamic linked list implementation; GDB shows the issue is on the node = node->next line in the "l_print" function of the linked-list ("LIST_CL.H" file). Anyone can help? I even tried "drawing debug" on paper but still I'm not getting the issue here.
Note: I report the whole code for both the insert and the print, in case it's useful. Therefore LIST.C file include the "switch case 6" to insert the element ("l_add" function in "LIST_CL.H" file) and the "switch case 1" to print the list ("l_print" function in "LIST_CL.H" file)
Note: The issue only happen when the list has one or more items. There's no errors when the list is empty ("list_cl" struct has NULL for both head and tail nodes)
LIST.C:
#include <stdio.h>
#include <string.h> //for strcpy
#include "cl_list.h"
#include "list_cl.h"
#define STRING_SIZE 25
int main(){
list_cl class = L_EMPTYLIST_CL;
puts("Select command:");
puts("0. Exit.");
puts("1. Insert node.");
puts("6. Print all nodes in the linked list.");
int k = 0;
scanf("%d", &k);
while(k != 0){
switch(k){
case 1:
char cf[17] = "";
char first_name[STRING_SIZE] = "";
char last_name[STRING_SIZE] = "";
getchar();
puts("Insert name:");
fgets(first_name, sizeof(first_name), stdin);
puts("Insert surname:");
fgets(last_name, sizeof(last_name), stdin);
puts("Insert fiscal code:");
fgets(cf, sizeof(cf), stdin);
client cliente;
strcpy(cliente.cf, cf);
cliente.first_name = first_name;
cliente.last_name = last_name;
class = l_add_cl(class, cliente);
puts("Node inserted.");
break;
case 6:
l_print(class);
break;
default:
break;
}
scanf("%d", &k);
}
}
LIST_CL.H:
list_cl l_add_cl(list_cl l, client p){
l_node node;
node.id = 1;
node.person = p;
node.next = NULL;
if(l.head == NULL){
//List is empty
l.head = &node;
l.tail = &node;
} else {
l.tail -> next = &node;
l.tail = &node;
}
return l;
}
void l_print(list_cl l){
l_node *node = NULL;
node = l.head;
while(node != NULL){
//client *cliente = &node->person;
//printf("ID Elemento: %d | Name: %s Surname: %s Fiscal Code: %s", node->id, cliente->first_name, cliente->last_name, cliente->cf);
node = node->next; // SEGMENTATION FAULT ERROR HERE!
}
}
CL_LIST.H:
#include "client.h"
typedef struct _node {
unsigned int id;
client person;
struct _node *next;
} l_node;
typedef struct {
l_node *head;
l_node *tail;
} list_cl;
#define L_EMPTYLIST_CL {NULL,NULL}
CLIENT.H:
typedef struct {
char cf[17];
char *first_name;
char *last_name;
} client;
Fixed code:
LIST.C:
#include <stdio.h>
#include <string.h> //for strcpy
#include "cl_list.h"
#include "list_cl.h"
#define STRING_SIZE 25
int main(){
list_cl class = L_EMPTYLIST_CL;
puts("Seleziona un comando:");
puts("0. Exit.");
puts("1. Insert one node.");
puts("6. Print all nodes.");
int k = 0;
scanf("%d", &k);
while(k != 0){
switch(k){
case 1:
char cf[17] = "";
//char first_name[STRING_SIZE] = ""; THIS CAUSE DATA INCONSISTENCY
//char last_name[STRING_SIZE] = ""; THIS CAUSE DATA INCONSISTENCY
char *first_name = malloc(sizeof(char)*STRING_SIZE);
char *last_name = malloc(sizeof(char)*STRING_SIZE);
getchar();
puts("Insert name:");
//fgets(first_name, sizeof(first_name), stdin); ISSUE WITH SIZE OF FIRST_NAME
fgets(first_name, sizeof(char)*STRING_SIZE, stdin);
puts("Insert surname:");
//fgets(last_name, sizeof(last_name), stdin); ISSUE WITH SIZE OF LAST_NAME
fgets(last_name, sizeof(char)*STRING_SIZE, stdin);
puts("IInsert fiscal code:");
fgets(cf, sizeof(cf), stdin);
client *cliente = malloc(sizeof(client));
strcpy(cliente->cf, cf);
cliente->first_name = first_name;
cliente->last_name = last_name;
class = l_add_cl(class, *cliente);
puts("Element inserted.");
break;
case 6:
l_print(class);
break;
default:
break;
}
puts("Select command:");
scanf("%d", &k);
}
}
LIST_CL.H
list_cl l_add_cl(list_cl l, client p){
l_node *node = malloc(sizeof(struct _node));
node->id = 1;
node->person = p;
node->next = NULL;
if(l.head == NULL){
//Empty list
l.head = node;
l.tail = node;
} else {
l.tail -> next = node;
l.tail = node;
l.tail -> next = NULL;
}
return l;
}
void l_print(list_cl l){
l_node *node = NULL;
node = l.head;
while(node != NULL){
client *cliente = &node->person;
printf("ID Element: %d | Name: %s Surname: %s Fiscal code: %s", node->id, cliente->first_name, cliente->last_name, cliente->cf);
node = node->next;
}
}
CL_LIST.H
#include "client.h"
typedef struct _node {
unsigned int id;
client person;
struct _node *next;
} l_node;
typedef struct {
l_node *head;
l_node *tail;
} list_cl;
#define L_EMPTYLIST_CL {NULL,NULL}
CLIENT.H
typedef struct {
char cf[17];
char *first_name;
char *last_name;
} client;
I've a problem with memory allocation for an hash table with linked list (for avoid collisions) in C.
I think that the problem is on allocation of an item.
I've made two scruct, one for the single item and one for the table.
The first have two pointer to next and prev item.
Please help me.
I stay on this code until 3 days.
The code :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define CAPACITY 50000
unsigned long hash(char *str) {
unsigned long int stringsum = 0;
for(; *str != '\0'; str++) {
stringsum += *str;
}
return stringsum % CAPACITY;
}
typedef struct item {
char *value;
char *key;
struct item *next;
struct item *prev;
} ht_item;
typedef struct hashtable {
ht_item **items;
int dim;
int count;
} HashTable;
HashTable* create_table(int size); HashTable* create_item(HashTable *table, char *value, char *key);
void print_table(HashTable* table, int dim);
int main(void) {
HashTable *table = create_table(CAPACITY);
table = create_item(table, "Giuseppe", "Nome");
print_table(table, CAPACITY);
return 0;
}
HashTable* create_item(HashTable *table, char *value, char *key) {
unsigned long index = hash(key);
printf("%u", index);
ht_item *_iterator; ht_item *prev;
for(_iterator = table->items[index], prev = NULL; _iterator != NULL; prev = _iterator, _iterator = _iterator->next);
_iterator = (ht_item*)malloc(sizeof(ht_item));
_iterator->key = (char*)malloc(200);
_iterator->value = (char*)malloc(200);
strcpy(_iterator->key, key);
strcpy(_iterator->value, value);
_iterator->next = NULL;
_iterator->prev = prev;
return table;
}
HashTable* create_table(int size)
{
HashTable *table = (HashTable*)malloc(sizeof(HashTable));
table->dim = size;
table->items = (ht_item**)calloc(size, sizeof(ht_item*));
for(int i = 0; i < size; i++){
table->items[i] = NULL;
}
return table;
}
void print_table(HashTable* table, int dim) {
for(int i = 0; i < CAPACITY; i++)
{
if(table->items[i] != NULL)
{ ht_item *_iterator = (ht_item*)malloc(sizeof(ht_item));
for(_iterator = table->items[i]; _iterator != NULL;
_iterator = _iterator->next)
{
printf("Key: %s\tValue: %s\n", _iterator->key, _iterator->value);
} free(_iterator);
}
}
}
Made some changes in your code. Please read through the blocks containing // CHANGE HERE comment.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define CAPACITY 50000
// CHANGE HERE - additional parameter, value to be used for modulo
unsigned long hash(char *str, unsigned int mod_value) {
unsigned long int stringsum = 0;
for(; *str != '\0'; str++) {
stringsum += *str;
}
// CHANGE HERE - use mod_value instead of CAPACITY
return stringsum % mod_value;
}
typedef struct item {
char *value;
char *key;
struct item *next;
struct item *prev;
} ht_item;
typedef struct hashtable {
ht_item **items;
int dim;
int count;
} HashTable;
HashTable* create_table(int size); HashTable* create_item(HashTable *table, char *value, char *key);
void print_table(HashTable* table, int dim);
int main(void) {
HashTable *table = create_table(CAPACITY);
table = create_item(table, "Giuseppe", "Nome");
print_table(table);
return 0;
}
HashTable* create_item(HashTable *table, char *value, char *key) {
// CHANGE HERE - function arguments validation
if (table == NULL)
{
return table;
}
if (value == NULL || key == NULL)
{
printf("Key or value is null\n");
return table;
}
// CHANGE HERE - pass table->dim to hash
unsigned long index = hash(key, table->dim);
printf("Index: %lu\n", index);
// CHANGE HERE - simplified the code a bit
ht_item* new_node = malloc(sizeof(ht_item));
new_node->key = malloc(200 * sizeof(char));
strncpy(new_node->key, key, 200);
new_node->value = malloc(200 * sizeof(char));
strncpy(new_node->value, value, 200);
// CHANGE HERE - if first node in index
if (table->items[index] == NULL)
{
table->items[index] = new_node;
return table;
}
ht_item *cur, *prev = NULL;
for(cur = table->items[index]; cur != NULL; prev = cur, cur = cur->next);
prev->next = new_node; // CHANGE HERE - it seems this line was missing
new_node->prev = prev;
new_node->next = NULL;
return table;
}
HashTable* create_table(int size)
{
HashTable *table = (HashTable*)malloc(sizeof(HashTable));
table->dim = size;
table->items = (ht_item**)calloc(size, sizeof(ht_item*));
for(int i = 0; i < size; i++){
table->items[i] = NULL;
}
return table;
}
void print_table(HashTable* table) {
// CHANGE HERE - function arguments validation
if (table == NULL)
{
printf("Table is null\n");
return;
}
// CHANGE HERE - change CAPACITY to dim
for(int i = 0; i < table->dim; i++)
{
//printf("i = %d [%d]\n", i, table->items[i] == NULL);
if(table->items[i] != NULL)
{
// CHANGE HERE - removed unnecessary malloc
ht_item *_iterator = NULL;
for(_iterator = table->items[i]; _iterator != NULL; _iterator = _iterator->next)
{
printf("Key: %s\tValue: %s\n", _iterator->key, _iterator->value);
}
}
}
}
The create_item function can and should be simplified.
I have put some comments inline.
HashTable* create_item(HashTable *table, char *value, char *key) {
// use modulo operator here, not in the hash function
unsigned long index = hash(key) % table->dim;
// nicer way of allocating
ht_item *insert = malloc(sizeof *insert);
// use strdup to avoid wasted memory and buffer overflows
insert->key = strdup(key);
insert->value = strdup(value);
// head insert rather than tail
insert->next = table->items[index];
table->items[index] = insert;
return table;
}
I dropped the use of the prev member. If you need that somewhere it's an exercise for you to add it. I don't think it's necessary for a simple hash table.
so basically I wrote a program to initialize, insert, and output the whole hash table. I thought I did pretty good, but there's many issues.
First issue being, some names are displayed with an additional weird character, why??
Second issue being, I can only input a size parameter (for initialize(size) function) of <8. Anything above 7 will output "Out of Space!" but why?? I thought I managed the space pretty well from what I was taught at uni:((
Please help!
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct list_node *node_ptr;
struct list_node
{
node_ptr next;
char *key;
char *value;
};
typedef node_ptr LIST;
typedef node_ptr position;
struct hash_table
{
LIST *list_ptr_arr;
unsigned int table_size;
};
typedef struct hash_table *HASHTABLE;
unsigned long long int
hash(const char *key, unsigned int hash_size)
{
unsigned long long int hash;
for(int i = 0; key[i]; i++)
{
hash = (hash<<32)+key[i];
}
return (hash%hash_size);
}
unsigned int
next_prime(int number)
{
int j;
for(int i = number; ; i++)
{
for(j = 2; j<i; j++)
{
if(i%j == 0){break;}
}
if(i==j){return j;}
}
}
HASHTABLE
initialize(unsigned int table_size)
{
HASHTABLE H;
H = (HASHTABLE) malloc(sizeof(struct hash_table));
if(H==NULL){printf("Out of Space!"); return 0;}
H->table_size = next_prime(table_size);
H->list_ptr_arr = (position*) malloc(sizeof(LIST)*H->table_size);
if(H->list_ptr_arr==NULL){printf("Out of Space!"); return 0;}
H->list_ptr_arr = (LIST*) malloc(sizeof(struct list_node)*H->table_size);
for(unsigned int i = 0; i<H->table_size; i++)
{
if(H->list_ptr_arr[i]==NULL){printf("Out of Space!"); return 0;}
H->list_ptr_arr[i]=NULL;
}
return H;
}
position
set(const char *key, const char *value)
{
position entry = (position) malloc(sizeof(struct list_node));
entry->value = (char*) malloc(strlen(value)+1);
entry->key = (char*) malloc(strlen(key)+1);
strncpy(entry->key,key,strlen(key));
strncpy(entry->value,value,strlen(value));
entry->next = NULL;
return entry;
}
void
insert(const char *key, const char *value, HASHTABLE H)
{
unsigned int slot = hash(key, H->table_size);
node_ptr entry = H->list_ptr_arr[slot];
node_ptr prev;
if(entry==NULL)
{
H->list_ptr_arr[slot] = set(key, value);
return;
}
while(entry!=NULL)
{
if(strcmp(entry->key, key)==0)
{
free(entry->value);
entry->value = malloc(strlen(value)+1);
strncpy(entry->value,value,strlen(value));
return;
}
prev = entry;
entry = prev->next;
}
prev->next = set(key, value);
}
void
dump(HASHTABLE H)
{
for(unsigned int i = 0; i<H->table_size; i++)
{
position entry = H->list_ptr_arr[i];
if(H->list_ptr_arr[i]==NULL){continue;}
printf("slot[%d]: ", i);
for(;;)
{
printf("%s|%s -> ", entry->key, entry->value);
if(entry->next == NULL)
{
printf("NULL");
break;
}
entry = entry->next;
}
printf("\n");
}
}
int main()
{
HASHTABLE H = initialize(7);
insert("name1", "David", H);
insert("name2", "Lara", H);
insert("name3", "Slavka", H);
insert("name4", "Ivo", H);
insert("name5", "Radka", H);
insert("name6", "Kvetka", H);
dump(H);
return 0;
}
Then I tried to change it up a bit:
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct list_node *node_ptr;
struct list_node
{
node_ptr next;
char *key;
char *value;
};
typedef node_ptr LIST;
typedef node_ptr position;
struct hash_table
{
LIST *list_ptr_arr;
unsigned int table_size;
};
typedef struct hash_table *HASHTABLE;
unsigned long long int
hash(const char *key, unsigned int hash_size)
{
unsigned long long int hash;
for(int i = 0; key[i]; i++)
{
hash = (hash<<32)+key[i];
}
return (hash%hash_size);
}
unsigned int
next_prime(int number)
{
int j;
for(int i = number; ; i++)
{
for(j = 2; j<i; j++)
{
if(i%j == 0){break;}
}
if(i==j){return j;}
}
}
HASHTABLE
initialize(unsigned int table_size)
{
HASHTABLE H;
H = (HASHTABLE) malloc(sizeof(struct hash_table));
if(H==NULL){printf("Out of Space!1"); return 0;}
H->table_size = next_prime(table_size);
H->list_ptr_arr = (position*) malloc(sizeof(LIST)*H->table_size);
if(H->list_ptr_arr==NULL){printf("Out of Space!2"); return 0;}
H->list_ptr_arr = (LIST*) malloc(sizeof(struct list_node)*H->table_size);
for(unsigned int i = 0; i<H->table_size; ++i)
{
if(H->list_ptr_arr[i]==NULL){printf("Out of Space!3"); return 0;}
H->list_ptr_arr[i]->value="HEAD";
H->list_ptr_arr[i]->next=NULL;
}
return H;
}
void
insert(const char *key, const char *value, HASHTABLE H)
{
unsigned int slot = hash(key, H->table_size);
LIST entry = H->list_ptr_arr[slot], newNode;
newNode = (position) malloc(sizeof(struct list_node));
if(newNode==NULL){printf("Out of Space4!"); return;}
newNode->next = entry->next;
strncpy(newNode->key,key,strlen(key));
strncpy(newNode->value,value,strlen(value));
entry->next = newNode;
}
void
dump(HASHTABLE H)
{
for(unsigned int i = 0; i<H->table_size; i++)
{
position entry = H->list_ptr_arr[i];
position p = entry->next;
if(p==NULL){continue;}
printf("slot[%d]: ", i);
for(;;)
{
printf("%s|%s -> ", p->key, p->value);
if(p->next == NULL)
{
printf("NULL");
break;
}
p = p->next;
}
printf("\n");
}
}
int main()
{
HASHTABLE H = initialize(4);
insert("name1", "David", H);
insert("name2", "Lara", H);
insert("name3", "Slavka", H);
insert("name4", "Ivo", H);
insert("name5", "Radka", H);
insert("name6", "Kvetka", H);
dump(H);
return 0;
}
Thank you!
I modified the second piece of code, it runs correctly on my computer.
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 256
// typedefing struct list_node multiple times is confusing, so I remove these typedefs
struct list_node {
struct list_node *next;
// strings need storage space in the memory,
// declaring key and value as array here can save some calls to malloc()
char key[MAX_SIZE];
char value[MAX_SIZE];
};
struct hash_table {
struct list_node **list_ptr_arr;
unsigned int table_size;
};
// it's better not to hide pointer type using typedef
typedef struct hash_table HASHTABLE;
unsigned long long int hash(const char *key, unsigned int hash_size) {
// hash is not initialized originally (the value is choosed randomly)
unsigned long long int hash = 5;
for (int i = 0; key[i]; i++) {
hash = (hash << 32) + key[i];
}
return (hash%hash_size);
}
unsigned int next_prime(int number) {
int j;
for (int i = number; ; i++) {
for (j = 2; j < i; j++) {
if (i%j == 0) { break; }
}
if (i == j) { return j; }
}
}
HASHTABLE *initialize(unsigned int table_size) {
HASHTABLE *H;
// you don't need to type cast malloc() result in C
H = malloc(sizeof(*H));
H->table_size = next_prime(table_size);
// I suppose list_ptr_arr is a pointer to an array of struct list_node * object
H->list_ptr_arr = malloc(sizeof(*(H->list_ptr_arr)) * H->table_size);
for (unsigned int i = 0; i < H->table_size; ++i) {
// malloc() for H->list_ptr_arr only allocated area for struct list_node * array, the struct list_node pointed to is not allocated yet, so malloc() here
H->list_ptr_arr[i] = malloc(sizeof(*(H->list_ptr_arr[i])));
strcpy(H->list_ptr_arr[i]->value, "HEAD");
H->list_ptr_arr[i]->next = NULL;
}
return H;
}
void insert(const char *key, const char *value, HASHTABLE *H) {
unsigned int slot = hash(key, H->table_size);
struct list_node *entry = H->list_ptr_arr[slot], *newNode;
newNode = malloc(sizeof(*newNode));
newNode->next = entry->next;
// strlen() doesn't count the '\0', just use strcpy here
strcpy(newNode->key, key);
strcpy(newNode->value, value);
entry->next = newNode;
}
void dump(HASHTABLE *H) {
for (unsigned int i = 0; i < H->table_size; i++) {
struct list_node *entry = H->list_ptr_arr[i];
struct list_node *p = entry->next;
if (p == NULL) { continue; }
printf("slot[%d]: ", i);
for (;;) {
printf("%s|%s -> ", p->key, p->value);
if (p->next == NULL) {
printf("NULL");
break;
}
p = p->next;
}
printf("\n");
}
}
int main() {
HASHTABLE *H = initialize(4);
insert("name1", "David", H);
insert("name2", "Lara", H);
insert("name3", "Slavka", H);
insert("name4", "Ivo", H);
insert("name5", "Radka", H);
insert("name6", "Kvetka", H);
dump(H);
return 0;
}
P.S. Don't forget to free the hashtable.
Im doing this program for managing students enrolled in each subject.
The system is composed by a linked list of subjects and a linked list of students. Each subject has a linked list of pointers for its students.
Each student has a list of pointers to their respective subjects.
None of the linked lists have headers.
Im trying to create the function to build the list of pointers to the subjects of each student but i dont understand how can i create it.
The structs i have so far are:
typedef struct node_subject * ListSubjects;
typedef struct node_subject {
char *name;
struct node_ptrStudent *Students;
ListSubjects next;
}NodeSubject;
typedef struct node_student * ListStudents;
typedef struct node_student {
char *name;
int num;
struct node_ptrSubject *Subjects;
ListStudents next;
}NodeStudent;
typedef struct node_ptrSubject * ListPtrSubjects;
typedef struct node_ptrSubject {
ListSubjects subjects;
ListPtrSubjects next;
}ListPtrSubjects;
typedef node_ptrStudent * ListPtrStudents;
typedef struct node_ptrStudent {
ListStudents student;
ListPtrStudents next;
}ListPtrStudents;
void createListPtrSubjects (ListSubjects);
The Linux kernel style says "It’s a mistake to use typedef for structures and pointers." https://www.kernel.org/doc/html/v4.10/process/coding-style.html#typedefs; whether or not one agrees with this, I think you have to many typedef; it's kind of confusing.
If you were programming a relational database, which you kind of are, this would be an associative entity; see https://en.wikipedia.org/wiki/Associative_entity. Also, make sure that your subjects have a primary key.
For example,
#include <stdlib.h> /* EXIT_ realloc */
#include <limits.h> /* INT_MAX */
#include <errno.h> /* errno */
#include <stdio.h> /* perror printf */
#include <assert.h> /* assert */
struct Subject {
int id; /* Primary key. */
const char *name;
struct Takes *takes_head;
};
struct Student {
int id; /* Primary key. */
const char *name;
struct Takes *takes_head;
};
/* (Weak) Associative entity. */
struct Takes {
int subject_id, student_id; /* Compound key. */
struct Takes *next_subject, *next_student;
};
static struct School {
struct Subject *subjects;
int subjects_no;
struct Student *students;
int students_no;
} school;
static struct Subject *lookup_subject(const int id) {
if(id >= school.subjects_no) return 0;
return school.subjects + id;
}
static struct Subject *add_subject(const char *name) {
struct Subject *subjects, *s;
assert(name);
if(school.subjects_no == INT_MAX) { errno = ERANGE; return 0; }
/* fixme: realloc is slow; eg, double capacity. */
if(!(subjects = realloc(school.subjects,
sizeof *school.subjects * (school.subjects_no + 1)))) return 0;
school.subjects = subjects;
s = school.subjects + school.subjects_no;
s->id = school.subjects_no;
s->name = name;
s->takes_head = 0;
school.subjects_no++;
return s;
}
/* May output in a static buffer. */
static const char *subject_to_string(const int id) {
struct Subject *const subject = lookup_subject(id);
static char str[256] = ""; /* Static buffer. */
if(!subject) { sprintf(str, "<subject id %d>", id); return str; }
return subject->name;
}
static struct Student *lookup_student(const int id) {
if(id >= school.students_no) return 0;
return school.students + id;
}
static struct Student *add_student(const char *name) {
struct Student *students, *s;
assert(name);
if(school.students_no == INT_MAX) { errno = ERANGE; return 0; }
if(!(students = realloc(school.students,
sizeof *school.students * (school.students_no + 1)))) return 0;
school.students = students;
s = school.students + school.students_no;
s->id = school.students_no;
s->name = name;
s->takes_head = 0;
school.students_no++;
printf("%s is assigned id %d.\n", s->name, s->id);
return s;
}
/* May output in a static buffer. */
static const char *student_to_string(const int id) {
struct Student *const student = lookup_student(id);
static char str[256] = ""; /* Static buffer. */
if(!student) { sprintf(str, "<student id %d>", id); return str; }
return student->name;
}
static struct Takes *lookup_takes(const int student_id, const int subject_id) {
const struct Student *const student = lookup_student(student_id);
struct Takes *t;
if(!student) return 0;
for(t = student->takes_head; t && t->subject_id != subject_id; t = t->next_student);
return t;
}
static struct Takes *add_takes(const int student_id, const int subject_id) {
struct Subject *const subject = lookup_subject(subject_id);
struct Student *const student = lookup_student(student_id);
struct Takes *t = lookup_takes(student_id, subject_id);
printf("%s enrols in %s.\n", student_to_string(student_id),
subject_to_string(subject_id));
/* Already have it. */
if(t) return t;
/* Or else make a new. */
if(!subject || !student) { errno = EDOM; return 0; }
if(!(t = malloc(sizeof *t))) return 0;
t->subject_id = subject_id;
t->student_id = student_id;
t->next_subject = subject->takes_head, subject->takes_head = t;
t->next_student = student->takes_head, student->takes_head = t;
return t;
}
static void print_subject(const int subject_id) {
struct Subject *const subject = lookup_subject(subject_id);
struct Takes *t;
printf("_Subject: %s._\n", subject_to_string(subject_id));
if(!subject) return;
for(t = subject->takes_head; t; t = t->next_subject)
printf("%s takes %s.\n", student_to_string(t->student_id),
subject_to_string(t->subject_id));
}
static void print_student(const int student_id) {
struct Student *const student = lookup_student(student_id);
struct Takes *t;
printf("_Student: %s._\n", student_to_string(student_id));
if(!student) return;
for(t = student->takes_head; t; t = t->next_student)
printf("%s takes %s.\n", student_to_string(t->student_id),
subject_to_string(t->subject_id));
}
int main(void) {
const char *why = 0;
do { /* Try. */
struct Subject *subject;
struct Student *student;
int herbology_id, defense_id, potions_id;
int hermione_id, ron_id, harry_id;
why = "Herbology";
if(!(subject = add_subject(why))) break;
herbology_id = subject->id;
why = "Defense";
if(!(subject = add_subject(why))) break;
defense_id = subject->id;
why = "Potions";
if(!(subject = add_subject(why))) break;
potions_id = subject->id;
why = "Hermione";
if(!(student = add_student(why))) break;
hermione_id = student->id;
why = "Ron";
if(!(student = add_student(why))) break;
ron_id = student->id;
why = "Harry";
if(!(student = add_student(why))) break;
harry_id = student->id;
why = "enrol";
if(!add_takes(hermione_id, defense_id)
|| !add_takes(hermione_id, potions_id)
|| !add_takes(hermione_id, herbology_id)
|| !add_takes(ron_id, herbology_id)
|| !add_takes(harry_id, potions_id)) break;
print_subject(herbology_id);
print_subject(defense_id);
print_subject(potions_id);
print_student(hermione_id);
why = 0;
} while(0); if(why) perror(why); /* Catch. */
/* fixme: free memory in 'final' block. Remember to free Takes. */
return why ? EXIT_FAILURE : EXIT_SUCCESS;
}
I am working on a program that uses a binary search tree (as an exercise).
My problem is that when I try to add a customer(in the middle of my code lines 65-69) I get an error that BS_node is undeclared, though I insert struct BST_node *root in this function..
Part of my code is below, just for the readers to read it easier, if requested I can upload the full code ! Thanks!
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_STRING 50
void flush();
struct customer {
char *name;
char *address;
char *email;
};
struct double_linked_list {
struct customer *data;
struct double_linked_list *previous;
struct double_linked_list *next;
};
struct double_linked_list *customers_head=0;
struct BST_node {
struct double_linked_list *data;
struct BST_node *left;
struct BST_node *right;
};
struct BST_node *BST_email_root = 0;
struct BST_node *BST_find_customer(struct BST_node *root, char *email) {
if (root==NULL)
return NULL;
if (strcmp(email,root->data->data->email)==0)
return root;
else
{
if (strcmp(email,root->data->data->email)==-1)
return BST_find_customer(root->left,email);
else
return BST_find_customer(root->right,email);
}
}
void find_customer() {
char email[MAX_STRING];
struct double_linked_list *l;
struct BST_node *b;
printf("Give the email of the customer (up to %d characters) : ", MAX_STRING-1);
gets(email);
b = BST_find_customer(BST_email_root, email);
if (b==0)
printf("There is no customer with this email.\n");
else
{
l = b->data;
printf("Customer found! \n");
printf("Name : %s\n", l->data->name);
printf("Address : %s\n", l->data->address);
printf("Email : %s\n", l->data->email);
}
}
struct BST_node *new_BST_node(struct BST_node *root, struct double_linked_list *l)
{
if (root==NULL);
{
root = (BST_node *) malloc (sizeof(BST_node ));
if (root==NULL)
{
printf("Out of Memory!");
exit(1);
}
root->data=l;
root->left=NULL;
root->right=NULL;
}
if (strcmp(l->data->email,root->data->data->email)==-1)
root->left =new_BST_node(root->left,l);
else root->right =new_BST_node(root->right,l);
return root;
};
struct double_linked_list *new_customer()
{
char name[MAX_STRING], address[MAX_STRING], email[MAX_STRING];
struct BST_node *b;
struct double_linked_list *l;
struct customer *c;
printf("\nADDING NEW CUSTOMER\n=\n\n");
printf("Give name (up to %d characters): ", MAX_STRING-1);
gets(name);
printf("Give address (up to %d characters): ", MAX_STRING - 1);
gets(address);
printf("Give email (up to %d characters): ", MAX_STRING - 1);
gets(email);
b = BST_find_customer(BST_email_root, email);
if (b)
{
printf("Duplicate email. Customer aborted.\n");
return 0;
}
c = (struct customer *) malloc(sizeof(struct customer));
if (c == 0)
{
printf("Not enough memory.\n");
return 0;
}
c->name = strdup(name); // check for memory allocation problem
if (c->name == 0) return 0;
c->address = strdup(address); // check for memory allocation problem
if (c->address == 0) return 0;
c->email = strdup(email); // check for memory allocation problem
if (c->email == 0) return 0;
l = (struct double_linked_list*) malloc(sizeof(struct double_linked_list));
if (l == 0)
{
printf("Not enough memory.\n");
free(c->name);
free(c->address);
free(c->email);
free(c);
return 0;
}
l->data = c;
l->previous = 0;
l->next = customers_head;
if (customers_head)
customers_head->previous = l;
customers_head = l;
BST_email_root = new_BST_node(BST_email_root, l);
return l;
}
void displaymenu() {
printf("\n\n");
printf("1. New customer\n");
printf("2. Find customer using email\n");
printf("0. Exit\n\n");
printf("Give a choice (0-6) : ");
}
void flush()
{
char ch;
while ((ch = getchar()) != '\n' && ch != EOF);
}
int main() {
int choice;
do {
displaymenu();
scanf("%d", &choice);
flush();
switch (choice) {
case 1:
new_customer();
break;
case 2:
find_customer();
break;
} while (choice != 0);
return 0;
}
On the line 69, you have to specify struct BST_node instead of BST_node:
root = (struct BST_node *) malloc (sizeof(struct BST_node ));
As for the rest of the code: read the manual for gets, it's clearly a function one should not use, I'd advise replacing it with fgets. There's also a little closing bracket missing in your final switch (line 178).