Thread: Appending content in the middle of a text file

Hi, I am doing a forum in C as my mini project. The idea is like any other forum. A user enters a query and other users reply to it. But it creates a problem here. After adding queries, if I wish to reply to query in between then it adds a redundant entry in file. 1st entry is the original query without reply and 2nd entry is the same query now with a reply added.
I want only 1 entry of the query along with replies.

Here is the code:

Code:

#include<stdio.h>
#include<stdlib.h>
#include<conio.h>
#include "var.c"
int check_count();
void add_query();
void add_reply();
void view_all();
void main()
{
	int user_typ,op_typ;
	clrscr();	
	printf("\nWELCOME\n");	
	
	recsize=sizeof(q);
	while(op_typ!=0)
	{
		printf("\n\n1.Add a new entry\n2.View all entries\n3.Reply to an entry\n0.Exit");
		printf("\nEnter your choice here");
		scanf("%d",&op_typ);
		switch(op_typ)
		{
			case 1:
			{
				add_query();


			}
			break;


			case 2:
			{
				view_all();
			}
			break;


			case 3: add_reply();
			break;
		}


	}
}


//Check the count of query to be posted
int check_count()
{
	FILE *qp;
	qp=fopen("queries.txt","rb+");
	while(fread(&q,sizeof(q),1,qp)==1)
	{
	}
	return q.qid+1;
}


//add a new query
void add_query()
{
	FILE *fp;
	int query_no,u_cat;
	fp=fopen("queries.txt","ab+");
	if(fp==NULL)
	{
		printf("\nError in creating/opening file");
	}
	query_no=check_count();
	q.qid=query_no;
	printf("\nEnter query no. %d: ",q.qid);
	fflush(stdin);
	gets(q.question);
	printf("\nselect which category you belong to:\n1.Student\n2.Professor\n3.Expert");
	printf("\nEnter your input here: ");
	scanf("%s",q.user_cat);
	fseek(fp,0,SEEK_END);
	fwrite(&q,sizeof(q),1,fp);
	fclose(fp);
	printf("\nYou entered: %s ",q.question);
	printf("\nCategory: %s ",q.user_cat);
}


//Display queries posted
void view_all()
{
	FILE *fp;
	fp=fopen("queries.txt","rb+");
	clrscr();
	if(fp==NULL)
		printf("\nCannot open file");
	while(fread(&q,sizeof(q),1,fp)==1)
		printf("\nQuery No.%d\nQuery: %s\nCategory: %sReply: %s\n\n",q.qid,q.question,q.user_cat,q.reply);
	fclose(fp);
}


void add_reply()
{
	FILE *fp,*fr;
	char another,ch;
	int query_id;
	another='Y';
	fp=fopen("queries.txt","a+");
	fr=fopen("replies.txt","w+");
	if(fp==NULL)
	{
		printf("\nCannot open file");
	}
	if(fp==NULL)
		printf("\nCannot open file");
	while(another=='Y')
	{
		printf("\nEnter the query no. to which you wish to add a reply: ");
		scanf("%d",&query_id);
		while(fread(&q,sizeof(q),1,fp)==1)
		{
			if(q.qid==query_id)
			{
				printf("\nQuery: %s",q.question);
				printf("\nEnter your reply here: ");
				fflush(stdin);
				gets(q.reply)                         //The problem is here. Adds duplicate entries
				fseek(fp,- sizeof(q),SEEK_CUR);


				fwrite(&q,sizeof(q),1,fp);
				break;
			}
		}
		printf("\nAdd another reply?(Y/N)");
		fflush(stdin);
		another=getche();
	}
}

This is the file var.c where I have declared the structure:

Code:

#include<stdio.h>
#include<conio.h>
struct query
	{
		int qid;
		char question[3000];
		char user_cat[20];
		char reply[50][500];
	};
	struct query q;
	long int recsize;

Kindly advise.
Thanx

Maybe read K&R2, do the exercises, then start over from scratch?

How would you do it on paper? Learn to think, come up with a solution and then turn your solution into "code".

first thing to do dont use fgets and fflush

Thanx. But I am still confused regarding the appending at specific position to a file concept.

The issue is that you need to insert text into the middle of a file, not append to the file. You may want to start off by trying to do this with a large ram buffer that contains the entire text file.

Is there a way to insert data in between without the exact byte of insertion?

You can't "insert data in between" you can only replace existing data. If you want to insert something you will need to create a new file, write the information that you want before your "new" data then write your "new" data followed by the rest of the data the original file contained.

Jim

What do you mean by "byte of insertion"?

Have you tried:

- Open existing file ("file 1")
- Create new file ("file 2")
- While there's no line to insert, copy line from "file 1" to "file 2"
- When there is a line to insert, add that line to "file 2"
- While not at the end of file, copy line from "file 1" to "file 2"
- Close "file 1" and "file 2"
- Delete "file 1"
- Rename "file 2" to "file 1"

You could also read the entire file into memory, add the new line where it belongs, and overwrite the existing file with the updated data.