I was trying to scan a file and add the data into the link list ,then print the operation into an output file. I succeed in printing the operation to the output file, but the content of my link list is empty when I try to access it.
I then check the address of each node created and linked and found no problem, when it is inside the function the link list worked fine but not in main().
Input.txt
3
1 Coding Mark Programming
1 Cooking Minnie Culinary
1 Gardening Penny Botany
This code is not completed but it contain my problem:
#include<stdio.h>
#include<ctype.h>
#include<string.h>
struct book {
char *title;
char *author;
char *subject;
};
struct library {
struct book collection;
int num_books;
struct library *next;
};
void AddBook(FILE *IF, FILE *OF, struct library** thislib);//function prototype
int main(void){
FILE *IF,*OF;
int sel,numOp,i;
struct library *Lib=NULL;//declare head pointer
if(((IF=fopen("library.txt","a+"))==NULL)||((OF=fopen("output.txt","w"))==NULL)){//open input and output file
printf("File cannot be open!");
}
else{
fscanf(IF," %d",&numOp); //scan the number of operation from file
for(i=0;i<numOp;i++){ //Loop according to number of operation
if(feof(IF)) //if file pointer reach EOF break
break;
fscanf(IF," %d",&sel); //scan the type of operation
switch(sel){
case 1:
AddBook(IF,OF,&Lib); //add the book if sel is 1
break;
case 2:
break;
}
printf("%s ", Lib->collection.title); // print the title of the book but it show nothing
}
}
return 0;
}
void AddBook(FILE *IF, FILE *OF, struct library** thislib){
char title[30],author[30],subject[20]; //declare variable to hold data
struct library *temp=NULL; //create a new node
struct library *ptr=*thislib; //create a pointer that point to head of link list
temp=(struct library*)malloc(sizeof(struct library)); //allocate memory for the new node
fscanf(IF," %s %s %s" ,title,author,subject);
temp->collection.title=title; // put the data into link list
temp->collection.author=author;
temp->collection.subject=subject;
temp->next=NULL;
if((*thislib)==NULL){
(*thislib)=temp; // if there is no content in link list put temp into head
}
else{
while (ptr->next!=NULL)
{
ptr=ptr->next; //put node at the end of link list
}
ptr->next=temp;
}
fprintf(OF,"The book %s author %s subject %s has been added to the library.\n",title,author,subject);
printf("%s ",(*thislib)->collection.title); //this work fine but it keep updating, weren't it suppose to have the same value
}