How to get C code to print to output file? - c

Question

I have a code that sorts a list, I can get it to sort when the list is hardcoded. I am now attempting to implement getting the list from an input file and running it the same way through the code then printing it to an output file. I am trying to get a scanned list from an input file to go through what I have (that is working) for sorting and for the result to be printed to an output file.

Answer 1

You have assigned *tmp to head. But I can see that head had always been NULL. So the loop is never entered, and nothing is being inserted to the list.
So what we'd need to do it first initialize head to a node instance
typdef struct node
{
char* data;
struct node *prev;
struct node *next;
}node;
head = malloc(sizeof(node));
then we assign it data.
head->attribute = value;
finally we set this pointer location value to our tmp pointer as well.
tmp = head;
no we can proceed with our loop
strings in C are represented as an array of chars, whose stored location points to the first element of the char array. the array must also end with a NULL chat '\0'. note that strlen(str) will return length of string without the NULL char so you must add 1 while mallocing to take this into sconsideration. i would advise not messing with strings unless absolutely necessary. by that I mean trying to manually manipulate them. this will introduce another set of problems not related to what we're working on in general. we should just use strncar(), strncpy() methods until c style strings become completely intuitive.

Answer 2

I hope I understood right your question. I tried to fix the program like it will read a file and make a list of the data in the file.
I fixed some issues;
For the transverse function, i added a for loop and printed the data using %c.
while (temp != NULL) {
for(i=0; temp->data[i]!='\0'; i++) {
printf("%c\n", temp->data[i]);
}
temp = temp->next;
}
I changed the insertAtEnd function like this;
void insertAtEnd(FILE* f, char* data)
And naturally, in main function, calling this function changed like;
insertAtEnd(ifp, result[i]);
By the way for the following statement, my complier wanted me to express the temp as char, it said it was the first use of this. It also seems like you entered a space after &.
insertAtEnd(ofp, &temp);
I added the following statements to the main function;
argc -= optind;
argv += optind;
I also changed this ifp= fopen(ifilename, "r"); statement with this ifp= fopen("ifilename.txt", "r");statement. I opened a text file named ifilename.txt and wrote some data there.
EDIT:
Ok so if you want to print the strings to an output file and you want to print the words in the lines individually, you will change the code doing the following things:
I changed the struct's data with an array, gave it an expected maximum line length with a sharp defined MAX_LEN;
struct node
{
char* data[MAX_LEN];
struct node *prev;
struct node *next;
};
I changed the insertAtEnd function again because I scanned the file in main function, made an array of the strings, sent it to this function and added it to the end of the list. I used this piece of code in main fuction:
char* result[count];
char* temp = (char*)malloc(sizeof(char));
while (fgets(temp, sizeof(temp), ifp))
{
result[count] = (char*)malloc(sizeof(char)*20);
strcpy(result[count], temp);
insertAtEnd(result, count);
count++;
}
count is the number of strings in the file. I also sent this number to insertAtEnd function;
void insertAtEnd(char* data[], int size)
{
//Create a new node
struct node *newnode = (struct node*)malloc(sizeof(struct node));
newnode->data[size] = data[size];
if (newnode->data[size] != NULL) {
...
I wanted to use the output file you opened in the main function, so I sent this file and sent the count -number of strings- to the printing function transverse like this;
void traverse(FILE *of, int size)
{
int i;
// List is empty
if (head == NULL) {
printf("\nList is empty\n");
return;
};
// Else print the Data
struct node* temp;
temp = head;
while (temp != NULL) {
for(i=0; i<size; i++) {
fputs(temp->data[i], of);
temp = temp->next;
}
fprintf(of, "\n");
}
}
Also in main function, calling this function will be changing like;
traverse(ofp, count);