How to change value of a string in binary tree? - c

Question

This function update() should suppose to the this, it scans information from file stream upd, number of the PC and its new IP address. It should scan the tree looking for PC's that have same red_br and s_red_br, and when it finds that PC, should update its IP address with the new IP address (s_ip_adress).
red_br and s_red_br are numbers of a PC; ip_adresa is PC's current IP address; s_ip_adresa is a new IP address.
RACUNAR is from:
typedef struct racunar_st {
int red_br;
char naziv[MAX_NAZIV];
char ip_adresa[MAX_IP];
int brzina;
struct racunar_st *left;
struct racunar_st *right;
} RACUNAR;
void update(FILE *upd, FILE *out, RACUNAR *root){
int s_red_br;
char s_ip_adresa[MAX_IP];
while(fscanf(upd, "%d %s", &s_red_br, s_ip_adresa) == 2){
int temp = root->red_br;
char temp1 = *root->ip_adresa;
if (temp == s_red_br){
temp1 = *s_ip_adresa;
}
}
}
I know that I am not going through the whole tree; I just wanted to test it and I can't even change the root.
Here you go the full program:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define MAX_NAZIV 20
#define MAX_VEL 10
#define MAX_IP 14+1
typedef struct racunar_st {
int red_br;
char naziv[MAX_NAZIV];
char ip_adresa[MAX_IP];
int brzina;
struct racunar_st *left;
struct racunar_st *right;
} RACUNAR;
void init_tree(RACUNAR **root){
*root = NULL;
}
void add_to_tree(RACUNAR *new, RACUNAR **root){
if(*root == NULL){
*root = new;
} else if(new->brzina <= (*root)->brzina){
add_to_tree(new, &((*root)->left));
} else if(new->brzina > (*root)->brzina) {
add_to_tree(new, &((*root)->right));
}
}
RACUNAR *create_new_item(int red_br, char naziv[], char ip_adresa[], int brzina){
RACUNAR *new = (RACUNAR *)malloc(sizeof(RACUNAR));
if(new == NULL){
printf("Nema dovoljno RAM-a!!!\n");
exit(21);
}
new->red_br = red_br;
strcpy(new->naziv, naziv);
strcpy(new->ip_adresa, ip_adresa);
new->brzina = brzina;
new->left = NULL;
new->right = NULL;
return new;
}
void read_tree_from(FILE *in, RACUNAR **root){
int tmp_red_br;
char tmp_naziv[MAX_NAZIV];
char tmp_ip_adresa[MAX_IP];
int tmp_brzina;
while(fscanf(in, "%d %s %s %d", &tmp_red_br, tmp_naziv, tmp_ip_adresa, &tmp_brzina) != EOF){
RACUNAR *new = create_new_item(tmp_red_br, tmp_naziv, tmp_ip_adresa, tmp_brzina);
add_to_tree(new, root);
}
}
void save_item_to(FILE *out, RACUNAR *x){
fprintf(
out, "%d %s %s %d\n",
x->red_br, x->naziv, x->ip_adresa, x->brzina
);
}
void save_tree_to(FILE *out, RACUNAR *root){
if(root != NULL){
save_tree_to(out, root->left);
save_item_to(out, root);
save_tree_to(out, root->right);
}
}
void destroy_tree(RACUNAR **root){
if(*root != NULL){
destroy_tree(&((*root)->left));
destroy_tree(&((*root)->right));
free(*root);
*root = NULL;
}
}
FILE *safe_fopen(char *filename, char *mode, int error_code){
FILE *fp = fopen(filename, mode);
if(fp == NULL){
printf("Nije moguce otvoriti fajl '%s'\n", filename);
exit(error_code);
}
return fp;
}
void update(FILE *upd, FILE *out, RACUNAR *root){
int s_red_br;
char s_ip_adresa[MAX_IP];
while(fscanf(upd, "%d %s", &s_red_br, s_ip_adresa) == 2){
int temp = root->red_br;
printf("%d\n", temp); // just testing to see if the function read data from file
printf("%d\n", s_red_br);
printf("%s\n", s_ip_adresa);
if ( temp == s_red_br){
*root->ip_adresa = *s_ip_adresa;
}
} printf("%s\n", root->ip_adresa); // checking if that ip adress has been changed
}
int main(int arg_num, char *args[]) {
if(arg_num != 4){
printf("Neispravan poziv programa!\n Pozvati sa: FILENAME_IN FILENAME_UPDATE FILENAME_OUT\n");
exit(1);
}
char *in_filename = args[1];
char *update_filename = args[2];
char *out_filename = args[3];
FILE *in = safe_fopen(in_filename, "r", 1);
FILE *upd = safe_fopen(update_filename, "r", 2);
FILE *out = safe_fopen(out_filename, "w", 3);
RACUNAR *root;
init_tree(&root);
read_tree_from(in, &root);
update(upd, out, root);
save_tree_to(out, root);
destroy_tree(&root);
fclose(in);
fclose(upd);
fclose(out);
return 0;
}

Answer 1

Second attempt:
Your update(upd, out, root); takes an input file, an output file and a pointer to an in-memory binary tree. Your save_tree_to(out, root); takes an output file and a pointer to root. Make up your mind which of those two functions will write to the file. Assuming we don't need the output file for update and that it can simply make changes within the root data structure, then:
void update( FILE *upd, RACUNAR *root )
{
int s_red_br;
char s_ip_adresa[MAX_IP];
while ( fscanf( upd, "%d %s", &s_red_br, s_ip_adresa ) == 2 )
{
RACUNAR *node = find( s_red_br, root );
if ( NULL != node )
{
strncpy(node->ip_adresa, s_ip_adresa, MAX_IP);
}
else
{
// Either insert new data or throw some kind of error here.
}
}
}
Your real problem is the fact that you have data structure that is not sorted by a primary key. Given a red_br value, you can't find the matching node without searching the entire tree.
RACUNAR* find( int red_br, RACUNAR *root )
{
RACUNAR *node = root;
while ( NULL != node )
{
if ( red_br == node->red_br )
{
return node;
}
// TODO: Need search code here, basically requires a tree sorted by red_br values.
node = NULL;
}
return node;
}