I already get how to add an int to a linked list in C but I need to add a string and it simply doesn't work.
The main function gets the data from the user and prints it in the show function after adding it to the linked list.
list and main
struct nlista{
char dado[10];
struct nlista *prox;
}*Head;
int main(){
int op;
char data[10];
Head = NULL;
printf("type a value: ");
scanf("%s",&data);
inserir(data);
printf("the element is : ");
show();
}
inserir(): add the element in the end of list
void inserir(char data){
nlista *novoelemento;
novoelemento = (struct nlista *)malloc(sizeof(struct nlista));
nlista *check;
check = (struct nlista *)malloc(sizeof(struct nlista));
novoelemento->dado = data;
if(Head == NULL){
Head = novoelemento;
Head->prox = NULL;
}
else{
check = Head;
while(check->prox != NULL)
check = check->prox;
check->prox = novoelemento;
novoelemento->prox = NULL;
}
show(): display the linked list
void show()
{
nlista *check;
check = (struct nlista *)malloc(sizeof(struct nlista));
check = Head;
if (check == NULL){
return;
}
while(check != NULL) {
printf("%s", check->dado);
check=check->prox;
}
printf("\n");
}
What am I missing? The compiler message is: invalid conversion from char* to char. in the line of inserir(data);
Sorry, but I found many mistakes in your code. I have written a very simple solution for your question. Kindly refer and correct your mistakes.
Value is nothing but, the string i.e data(in the code) passed as an argument in function inserir in the main function. Remember each node of the linked list consists of a string element and the pointer to the next node. The string can be of various length. step 1 and step 2 will take care of that(see the code). Hope you are clear now.
#include <stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct nlista{
char *data;
struct nlista *prox;
}Node;
Node * inserir(Node *, char *);
'''inserir function should return your head node'''
void show(Node *);
'''show function takes head node'''
int main()
{
char data[10];
Node * Head = NULL;
printf("Type a value: ");
scanf("%s",data);
Head = inserir(Head,data);
printf("the element is : ");
show(Head);
}
Node* inserir(Node *Head, char *value)
{
Node *novoelemento;
novoelemento = (Node *)malloc(sizeof(Node));
//step 1. allocate memory to hold word
novoelemento->data = malloc(strlen(value)+1);
//step 2. copy the current word
strcpy(novoelemento->data,value);
Node *check;
check = (Node *)malloc(sizeof(Node));
if(Head == NULL){
Head = novoelemento;
Head->prox = NULL;
}
else{
check = Head;
while(check->prox != NULL)
check = check->prox;
check->prox = novoelemento;
novoelemento->prox = NULL;
}
return Head;
}
void show(Node *Head)
{
//check is of Node type using which you traverse the list and print the values
Node *check;
check = (Node *)malloc(sizeof(Node));
check = Head;
if (check == NULL){
return;
}
while(check != NULL) {
printf("%s", check->data);
check=check->prox;
}
printf("\n");
}
Hope this will help you.
We have char dado[10]; but novoelemento->dado = data; As you discovered, this does not compile.
You seem to want strncpy(novoelemento->dado, data, 10)[9] = 0; This copies the string within data over and ensures it's properly null terminated.
If you have strlcpy, you can do it better as strlcpy(novoelemento->dado, data, 10);
Related
I'm trying to write and use linked list. When trying to print the list to the file the first string gets chained to the last node and it causes a segfault.
I've tried debugging and it led me nowhere.
It only happens using printListToFile(...) and readstl(...).
The code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "lists_c.h"
#define test "ijm digidimdimadam jjsklva /s4t\t \nmjam \nla kookaracha la kookaracha\n"
/*a method that creates a "blank" node, declares a the next node and points it to NULL, the char array is already initialized.*/
struct Node *makeNode();
struct Node *makeFullNode(struct Node *Next, char *Ptr);
struct Node *readFile(char *path);
struct Node *readstl(char*);
void printList(struct Node *head);
void insertToList(struct Node *node, char *str);
void printListToFile(char *path, struct Node *head);
int main(int argc, char *argv[])
{
struct Node *head;
head = (struct Node *)malloc(sizeof(struct Node));
printf("this is mmn 23 Q3, a func that stores a file in a linked list and then prints it.\n");/*
printf("%s\n",argv[1]);
if (argc == 2) { */
head = readFile("tester1.txt");
printList(head);
printListToFile("test.tmp", head);
insertToList(head->next, test);
printf("head");
free(head);
/*}
else if (argc > 2) {
printf("Too many arguments supplied.\n");
} else {
printf("One argument expected.\n");
}*/
return 0;
}
struct Node *makeNode()
{
struct Node *node;
node = (struct Node *)malloc(sizeof(struct Node));
if (node == NULL) {
printf("memory allocation failed\n");
return NULL;
}
node->next = NULL;
return node;
}
/*a method that creates a node with all values, declares a the next node and points it to the next node recieved
and changes the char array to the one recieved.*/
struct Node *makeFullNode(struct Node *Next, char Ptr[])
{
struct Node *node;
node = (struct Node *)malloc(sizeof(struct Node));
node->next = (struct Node *)malloc(sizeof(struct Node));
node->ptr[NICE] = Ptr[NICE];
node->next = Next;
return node;
}
/*the method that reads the file into the list into the char array of each node and returns the head of the list */
struct Node *readFile(char *path)
{
FILE *fptr;
struct Node *curr, *head;
curr = (struct Node *)malloc(sizeof(struct Node));
head = (struct Node *)malloc(sizeof(struct Node));
if (curr == NULL || head == NULL) {
printf("memory allocation failed\n");
return NULL;
}
curr = head;
fptr = fopen(path,"r");
if (fptr == NULL) {
printf("error - failed to open file\n");
exit(0);
return NULL;
}
while (fgets(curr->ptr, NICE, fptr))/*if fgets returns NULL it means that we either reached EOF or error, both a reason to end the loop*/
{
curr->next = makeNode();
curr = curr->next;
}
if(ferror(fptr))/*checking if the loop ended for the right reason*/
{
printf("error - failed to read file\nthis is what we got so far\n");
}
printf("file succesfully read\n");
fclose(fptr);
free(curr);
return head;
}
/*the method that reads the file into the list into the char array of each node and returns the head of the list */
struct Node *readstl(char *path)/*!!!problem!!!*/
{
FILE *fptr;
int i, len;
struct Node *head;
head = (struct Node *)malloc(sizeof(struct Node));
fptr = fopen("readstrtofile.tmp", "w");
if (fptr == NULL) {
printf("error - failed to open file\n");
exit(0);
return NULL;
}
len = strlen(path);
for (i = 0; i < len && fputc(*(path + i), fptr) != EOF; i++);
if (ferror(fptr))/*checking if the loop ended for the right reason*/
{
printf("error - failed to read into file\nthis is what we got so far\n");
}
fclose(fptr);
head = readFile("readstrtofile.tmp");
remove("readstrtofile.tmp");
return head;
}
/*a method that prints the recieved list depending on the list to have the equal length rows.
as specified in mmn 12 tab creating uneven rows is acceptable therefor when ever there is tab in the file
the rows will appear uneven as to tab takes a place of one char but prints to 8 blank spaces in ubuntu */
void printList(struct Node *head)
{
struct Node *curr;
curr = (struct Node *)malloc(sizeof(struct Node));
if (head == NULL) {
printf("empty list\n");
return;
}
if (curr==NULL) {
printf("memory allocation failed\n");
return;
}
printf("this is the list printed nicely\n");
curr = head;
printf("%s\n", curr->ptr);
while (curr->next != NULL) {
curr = curr->next;
printf("%s\n", curr->ptr);
}
printf("\n/********************/\n");
}
/* a method that creates a new file named path and prints a list to it */
void printListToFile(char *path,struct Node *head)/*!!!problem!!!*/
{
struct Node *curr;
char c;
int i;
FILE *fptr;
curr = (struct Node *)malloc(sizeof(struct Node));
if (curr == NULL) {
printf("memory allocation failed\n");
exit(0);
}
curr = head;
fptr = fopen(path, "w+");
if (fptr == NULL) {
printf("error - failed to open file\n");
exit(0);
}
if (head == NULL) {
printf("empty list\n");
exit(0);
}
printf("this is the file %s printed nicely\n",path);
curr = head;
while (curr->next != NULL) {
printf("new node -> ptr -> %s\n",curr->ptr);
/*if(sizeof(curr->ptr)/sizeof(char)<=NICE)
{*/
for(i=0;i<NICE && (c = fputc(curr->ptr[i],fptr)) != EOF;i++);
printf("puting %s to file %s\n",curr->ptr,path);
curr = curr->next;
printf("bolili\n");
/*}
else
{
printf("lilibo\n");
break;
}*/
}
printf("\n/********************/\n");
}
/* a method that recievs a string turns it into a list and inserts it into another list */
void insertToList(struct Node *node, char *str)
{
struct Node *tail, *head;
tail = (struct Node *)malloc(sizeof(struct Node));
head = (struct Node *)malloc(sizeof(struct Node));
if (tail == NULL || head == NULL) {
printf("memory allocation failed\n");
return;
}
head = readstl(str);/*reading the string to a node*/
printList(head);
printf("\n/***********in insert*********/\n");
tail = head;
while (tail->next) {
tail = tail->next;
}/*getting tto the last node to connect it*/
strcpy(tail->ptr, node->next->ptr);/*connecting the lists*/
tail->next = node->next->next;
strcpy(node->ptr, head->ptr);
node->next = head->next;
printf("inserted string successfully\n");
}
/* a method that returns the size of the list*/
unsigned int sizeOfList(struct Node *head)
{
struct Node *tmp;
int size;
if (!(head))
return 0;
size = 1;
tmp = (struct Node *)malloc(sizeof(struct Node));
tmp = head;
while ((tmp = tmp->next))
size++;
return size;
}
header file
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define NICE 80
#define debug "\n/****************/\n"
/*the node structure of a the list which contains a string the size we choose is nice
to print by and a pointer to the next node in the list. */
struct Node {
char ptr[NICE];
struct Node *next;
};
/*makeNode - a method that returns a newely created node and sets all values to NULL values.*/
struct Node *makeNode();
/*makeFullNode - a method that return a newely created node with values set to params as listed below.
#param Next - tho ptr to the next node desired.
#param Ptr - the string that will go into the node ptr.*/
struct Node *makeFullNode(struct Node *Next, char *Ptr);
/*readFile - a method that reads a file into a linked list returning the head to that list.
it reads the file using fgets and a const to decide what size the node strings should be.
#param path - the name of the file to open.
#return the head of the list.*/
struct Node *readFile(char *path);
/*readstl - a method that reads a string into a linked list returning the head to that list.
it prints the list to a tmp file then reads the file using readFile.
#param path - the string to read.
#return the head of the list.*/
struct Node *readstl(char*);
/*printList - a method that prints the list to stdout.
it goes in loop on the nodes each time printing the node->ptr.
#param head - the head of the linked list.*/
void printList(struct Node *head);
/*insertToList - a method that inserts a string into list.
it creates a new list using readstl the connects the nodes using the basic method.
#param node - the node to override.
#param str - the string to insert.*/
void insertToList(struct Node *node, char *str);
/*a method that prints the list to stdout.
it goes in loop on the nodes each time printing the node->ptr.
#param head - the head of the linked list.*/
void printListToFile(char *path,struct Node *head);
/*sizeOfList - a method that returns how many node are in the list.
it goes in a while loop incresing counter by 1 each iteration.
#param head - the head of the list to measure.
#return the size of the list.*/
unsigned int sizeOfList(struct Node *head);
I think it is this line:
for(i=0;i<NICE && (c = fputc(curr->ptr[i],fptr)) != EOF;i++);
Why would fputc ever return EOF if everything goes right? It will try to write characters behind the ptr array. From the manpage of fputc:
fputc(), putc() and putchar() return the character written as an unsigned char cast to an int or EOF on error.
This means, your loop writes as long as fputc doesn't return an error code. But what you probably want, is writing either 80 (NICE is not a nice constant name) or strlen(curr->ptr) characters. Assuming based on your readFile function, you want both things as a limit. I would recommend rewriting this line as:
int len = strnlen(curr->ptr, 80);
if (fwrite(curr->ptr, 1, len, fptr) < 0) {
printf("error writing file");
}
or if the string is always null terminated:
if (fputs(curr->ptr, fptr) < 0) {
printf("error writing file");
}
Also ptr is not a good name for an array. It might confuse people or even you after some time, trying to understand the code. A better name would be value or text (even arr would be better, because it is not a pointer).
In readFile you have a loop in which you read a line and put it in curr->ptr and then create a new curr and link it to the previous curr.
This creates an extra empty curr at the end of the list which you don't need and so you free it later. Unfortunately, the next pointer of the previous node is still pointing at the empty node you just freed.
The easiest way to fix this without restructuring the loop a bit is to keep a record of the previous node, something like this:
struct Node* prev = NULL;
while (fgets(curr->ptr, NICE, fptr))/*if fgets returns NULL it means that we either reached EOF or error, both a reason to end the loop*/
{
curr->next = makeNode();
prev = curr;
curr = curr->next;
}
free(curr);
if (prev != NULL)
{
prev->next = NULL;
}
else
{
head = NULL; // For the empty file case. head == curr in this case
}
// The other clean up stuff
I have written a linked list program which stores data member as void *.
while trying to store annd print using scanf/printf functions, I am getting segmentation fault.
node definition -->
typedef struct node {
struct node *next;
void *data;
}node;
main function -->
head=(node *)malloc(sizeof(node));
if (head==NULL){
printf("error in allocation of memory\n");
exit(EXIT_FAILURE);
}
tail=(node*)create(head);
create function -->
void *create(node *current)
{
int user_choice;
while(current){
printf("\nEnter the data:");
scanf("%s",current->data);
printf("stored at %p\n",(void*)current->data);
printf("%s",(char*)current->data);
printf("\nType '1' to continue, '0' to exit:\n");
scanf("%d",&user_choice);
if(user_choice == 1){
current->next=(node*)malloc(sizeof(node));
current=current->next;
}
else{
current->next=NULL;
}
}
return current;
}
can anyone tell what is the correct argument for scanf & prinf should be..?
working code after incorporating points given in answers...
void *create(node *current)
{
node *temp;
int user_choice;
while(current){
printf("\nEnter the data:");
current->data=(char*)malloc(10*sizeof(char));
scanf("%s",current->data);
printf("stored at %p\n",(void*)current->data);
printf("%s",(char*)current->data);
printf("\nType '1' to continue, '0' to exit:\n");
scanf("%d",&user_choice);
if(user_choice == 1){
current->next=(node*)malloc(sizeof(node));
}
else{
current->next=NULL;
temp=current;
}
current=current->next;
}
return temp;
}
In your code,
scanf("%s",current->data);
is attempt to make use of an unitialized pointer, it invokes undefined behavior.
You need to follow either of bellow approach,
make the pointer point to valid chunk of memory (using malloc() and family for dynamic allocation, for example)
use an array.
You should first initialize data member of structure because
current->data = malloc("passes size here");
For putting data you have to typecast first this data because void is not storage type. void pointer can be used to point to any data type.
Like
*(char *)(current->data) = 1;
As others have said:
scanf("%s",current->data);
Is undefined in C. current->data needs to be pointing somewhere before you can store anything in it.
You should instead:
Accept input from scanf.
Store in temporary buffer.
Insert into linked list
print out whole linked list at the end
free() linked list at the end.
I also feel that your current void *create function is doing too much, and it would be easier to split up your code into different functions, just to make it easier to handle all the pointer operations, inserting etc.
To demonstrate these points, I wrote some code a while ago which does these things, and has been modified to help you with your code. It is not the best code, but it does use these points that will help you with your code.
Here it is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXSTRLEN 100
typedef struct node {
void *data;
struct node *next;
} node_t;
typedef struct {
node_t *head;
node_t *foot;
} list_t;
list_t *create_list(void);
node_t *generate_node(void);
list_t *insert_node(list_t *list, char *data);
void print_list(list_t *list);
void free_list(list_t *list);
int
main(int argc, char *argv[]) {
list_t *list;
char data[MAXSTRLEN];
int user_choice;
list = create_list();
while (1) {
printf("Enter the data: ");
scanf("%s", data);
printf("\nType '1' to continue, '0' to exit:\n");
if (scanf("%d",&user_choice) != 1) {
printf("Invalid input\n");
exit(EXIT_FAILURE);
}
if (user_choice == 1) {
list = insert_node(list, data);
} else {
list = insert_node(list, data);
break;
}
}
print_list(list);
free_list(list);
list = NULL;
return 0;
}
/* inserting at foot, you can insert at the head if you wish. */
list_t
*insert_node(list_t *list, char *data) {
node_t *newnode = generate_node();
newnode->data = malloc(strlen(data)+1);
strcpy(newnode->data, data);
newnode->next = NULL;
if (list->foot == NULL) {
list->head = newnode;
list->foot = newnode;
} else {
list->foot->next = newnode;
list->foot = newnode;
}
return list;
}
node_t
*generate_node(void) {
node_t *new = malloc(sizeof(*new));
new->data = NULL;
return new;
}
void
print_list(list_t *list) {
node_t *curr = list->head;
printf("\nlinked list data:\n");
while(curr != NULL) {
printf("%s\n", (char*)curr->data);
curr = curr->next;
}
}
list_t
*create_list(void) {
list_t *list = malloc(sizeof(*list));
if (list == NULL) {
fprintf(stderr, "%s\n", "Error allocating memory");
exit(EXIT_FAILURE);
}
list->head = NULL;
list->foot = NULL;
return list;
}
void
free_list(list_t *list) {
node_t *curr, *prev;
curr = list->head;
while (curr) {
prev = curr;
curr = curr->next;
free(prev);
}
free(list);
}
UPDATE:
Also note how I allocated memory for newnode->data?
Like this:
newnode->data = malloc(strlen(data)+1); //using buffer from scanf
This now means I can store data in this pointer, your current->data will need to do something similar.
working code-->
void *create(node *current)
{
node *temp;
int user_choice;
while(current){
printf("\nEnter the data:");
current->data=(char*)malloc(10*sizeof(char));
scanf("%s",current->data);
printf("stored at %p\n",(void*)current->data);
printf("%s",(char*)current->data);
printf("\nType '1' to continue, '0' to exit:\n");
scanf("%d",&user_choice);
if(user_choice == 1){
current->next=(node*)malloc(sizeof(node));
}
else{
current->next=NULL;
temp=current;
}
current=current->next;
}
return temp;
}
Please try with this
void *create(node *current)
{
int user_choice;
while(true){
if(current == NULL) {
current = (node *)malloc(sizeof(node));
current->data = NULL;
current->next = NULL;
}
printf("\nEnter the data:");
scanf("%s",current->data);
printf("stored at %p\n", (void *)current->data);
printf("%s",current->data);
//printf("%s",(char*)current->data);
printf("\nType '1' to continue, '0' to exit:\n");
scanf("%d",&user_choice);
if(user_choice == 1){
current->next=(node*)malloc(sizeof(node));
current=current->next;
}
else{
current->next=NULL;
tail = current;
current=current->next;
break;
}
}
return current;
}
Note: The element has to be initialized (ie; it has to be alloted with some memory) before we are trying to make use of it.
I'm having a problem with inserting a node at the end of a linked list. It's not being executed when the start node is not null and I don't understand the problem. Please help me out here. The function is called second time but is not going to the else block.
typedef struct token_Info
{
int linenumber;
char* token;
char value[200];
struct token_Info* next;
} token_Info;
token_Info *tokenlist;
token_Info* insert_at_end( token_Info *list,char *name)
{
printf("token identified \t");
token_Info *new_node;
token_Info *temp,*start;
start = list ;
char *tempname ;
tempname = name;
new_node= malloc(sizeof(token_Info));
new_node->token = malloc(sizeof(strlen(tempname)+1));
strcpy(new_node->token,tempname);
new_node->next= NULL;
// printf("%d",strlen(tempname));
if(new_node == NULL){
printf("nFailed to Allocate Memory");
}
if(start==NULL)
{
start=new_node;
return start;
}
else
{
printf("anvesh");
temp = start;
while(temp->next != NULL)
{
temp = temp ->next;
}
temp->next = new_node;
return temp;
}
}
tokenlist = insert_at_end(tokenlist,"TK_BEGIN");
tokenlist = insert_at_end(tokenlist,"TK_BEGIN1");
UPDATE
I found two bugs, the first was the head of the list was not being returned when appending the list. The other in the memory allocation for the token string which incorrectly used sizeof.
I repositioned the test of the malloc() return value, and added a second one. I removed several unnecessary temporary variables that were cluttering the code. I added two functions, show_list() and free_list(). Finally, remember that the value string field is still uninitialised.
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct token_Info
{
int linenumber;
char* token;
char value[200];
struct token_Info* next;
} token_Info;
token_Info* insert_at_end( token_Info *list, char *name)
{
token_Info *new_node, *temp;
new_node= malloc(sizeof(token_Info));
if(new_node == NULL){ // repositioned
printf("\nFailed to allocate node memory\n");
exit(1); // added
}
new_node->token = malloc(strlen(name)+1); // removed sizeof
if(new_node->token == NULL){ // added
printf("\nFailed to allocate token memory\n");
exit(1);
}
strcpy(new_node->token, name);
new_node->next= NULL;
if(list==NULL)
return new_node;
// append
temp = list;
while(temp->next != NULL)
temp = temp->next;
temp->next = new_node;
return list; // original head
}
void free_list( token_Info *list)
{
token_Info *temp;
while (list) {
temp = list->next;
free(list->token);
free(list);
list = temp;
}
}
void show_list( token_Info *list)
{
printf ("\nCurrent list:\n");
while (list) {
printf ("%s\n", list->token);
list = list->next;
}
}
int main(int argc, char **argv)
{
token_Info *tokenlist = NULL;
tokenlist = insert_at_end(tokenlist, "TK_BEGIN");
show_list(tokenlist);
tokenlist = insert_at_end(tokenlist, "TK_SECOND");
show_list(tokenlist);
tokenlist = insert_at_end(tokenlist, "TK_FINAL");
show_list(tokenlist);
free_list(tokenlist);
return 0;
}
Program output:
Current list:
TK_BEGIN
Current list:
TK_BEGIN
TK_SECOND
Current list:
TK_BEGIN
TK_SECOND
TK_FINAL
The question could also be whether you want tokenlist to be a running end of the list, or remain at the start.
As of right now, your first call:
tokenlist = insert_at_end(tokenlist,"TK_BEGIN");
has tokenlist being the only node in the list.
The second call tokenlist = insert_at_end(tokenlist,"TK_BEGIN1"); returns 'temp' which happens to also be the 'TK_BEGIN' node, ( ie, the first node )
If you want the return value to be the last element, you would return new_node instead of temp. If you want to retain the start, you would return start;
All that said:
The calls to it are not part of any function,
I just ran it with the calls in main and got this output:
int main(void){
tokenlist = insert_at_end(tokenlist,"TK_BEGIN");
tokenlist = insert_at_end(tokenlist,"TK_BEGIN1");
return 0;
}
$> ./a.out
token identified token identified anvesh
I have an issue creating linked list: I don't know where I do an error in code, could you help me? Here's the code:
#include <stdio.h>
#include <stdlib.h>
#define LENGTH 255
struct node {
int info;
struct node *next;
} *head = NULL;
int create(FILE **data){
char read[LENGTH];
printf("Write data file name: ");
scanf("%s", read);
*data = fopen (read, "r");
if (data == NULL) {
printf("Error reading given file.");
}
return 0;
}
int put_Symbols_into_list(FILE *data) {
struct node *new_node, *current;
char c;
printf("Data given: ");
while (!feof(data)){
new_node = (struct node*)malloc(sizeof (struct node));
c = fscanf(data, "%s", &new_node -> info);
printf("%s ", &new_node -> info);
if (head == NULL){
head = new_node;
current = new_node;
} else {
current -> next = new_node;
current = new_node;
}
}
}
int main() {
FILE *data;
struct node *n;
create(&data);
put_Symbols_into_list(data);
//display_List(n);
return 0;
}
Steps that I do: Read data file for string and put it new node; if HEAD node doesn't have any data in it, put the read data in it; else put it in new node. Cycle this until there is not data left in data file. You can create new data file and put data in there, like 1 0 1 1 2 3 4 5 6.
You are not putting current->next to NULL after adding a new node. That will make a problem when you try to go through a list, since you won't know where it ends. I hope that's the problem that you're facing with.
Also you're having redundant code, since current will always point to new_node after adding it. So you don't have to put it both in if and else block. Just an advice.
You forgot to make the last node point to NULL. This will be extremely important when you try to traverse your list and display it.
int put_Symbols_into_list(FILE *data)
{
struct node *new_node, *current;
char c;
printf("Data given: ");
while (!feof(data)){
new_node = (struct node*)malloc(sizeof (struct node));
c = fscanf(data, "%d", &new_node -> info);
printf("%d ", new_node->info);
if (head == NULL){
head = new_node;
current = new_node;
} else {
current->next = new_node;
current = new_node;
new_node->next = NULL; // << added
}
}
return 0;
}
In addition to the answers above, you are declaring current as a local variable in put_Symbols_into_list, and not initializing current. Each time you exit put_Symbols_into_list, the value of current may be lost. You either need to declare current as static struct node *current, pass it as a parameter, or declare it globally. I would favor the static approach in this setting.
So this is my code for the a linked list program. I know it's not that great, but it works. I want to change the ins() function so that new elements are inserted to the list by magnitude.. i.e., the last node on the list will contain the greatest integer, and the smallest the first. The integers are read in from a text file, and as you can see in main(), the INSERT and REMOVE commands in the text file are interpreted as commands to either insert (the following integer on the next line) into the list, or remove an element from the list. How can I do this with my existing code? I tried modifying my ins() function, but was unable to get my list ordered properly.
#include <stdio.h>
#include <stdlib.h>
struct node {
int number;
struct node *next;
};
/* prototypes */
void ins(struct node *llist, int number);
void rem(struct node *llist);
void sho(struct node *llist);
int main(void)
{
int number;
char command[6];
struct node *llist;
struct node *root;
llist = (struct node *)malloc(sizeof(struct node));
llist->number = 0;
llist->next = NULL;
root = llist;
printf("addr: \n\n%p,%p\n\n", &llist, &root);
FILE *file;
file = fopen("a3data.txt", "r");
if (file == NULL)
{
printf("\n----------------------------------------\n");
printf("| Error. Did not read file. Exiting. |\n");
printf("----------------------------------------\n\n");
exit(1);
}
else
{
while ((fscanf(file, "%s", command)) != EOF)
{
if((strcmp(command, "INSERT"))==0)
{
fscanf(file, "%d", &number);
printf("\nINSERT ", number);
ins(llist, number);
sho(llist);
}
else if((strcmp(command, "REMOVE"))==0)
{
printf("\n REMOVE ");
rem(llist);
sho(llist);
}
}
}
printf("\n");
free(llist);
return(0);
}
void ins(struct node *llist, int number)
{
while(llist->next != NULL)
{
llist = llist->next;
}
llist->next = (struct node *)malloc(sizeof(struct node));
llist->next->number = number;
llist->next->next = NULL;
}
void rem(struct node *llist)
{
while(llist->next->next != NULL)
{
llist = llist->next;
}
llist->next = NULL;
}
void sho(struct node *llist)
{
while(llist->next != NULL)
{
printf("%d ", llist->number);
llist = llist->next;
}
printf("%d", llist->number);
}
Modified function in your case
void ins(struct node *llist, int number)
{
struct node *llist1;
while(llist->next != NULL)
{
if (llist->next->number > number)
break;
llist = llist->next;
}
llist1 = (struct node *)malloc(sizeof(struct node));
llist1->number = number;
llist1->next = llist->next;
llist->next = llist1;
}
Your insert is simply adding the element in the tail. You have to write code to compare the present value of node(list->number) against the number to be inserted. If the current value is greater than the number to be inserted, then the number has to be inserted before the current node. For this, you will have to keep previous pointer also. The code, I have written, is just to understand the logic, Didn't check for correctness.
if(llist->number > innumber) {
node *newNode = (struct node *)malloc(sizeof(struct node);
newNode->number = innumber;
prevPointer->next = newNode;
newNode->next = llist;
}
in ins() function, instead of
while(llist->next != NULL)
use
while((llist->next != NULL) && (llist->number < number))
This will help you to sort while inserting itself.
Also in rem() function, you have to free the memory that you dynamically allocate.