User Name Password Register
DaniWeb IT Discussion Community
All
What is DaniWeb IT Discussion Community?
You're currently browsing the C++ section within the Software Development category of DaniWeb, a massive community of 456,584 software developers, web developers, Internet marketers, and tech gurus who are all enthusiastic about making contacts, networking, and learning from each other. In fact, there are 3,630 IT professionals currently interacting right now! Registration is free, only takes a minute and lets you enjoy all of the interactive features of the site.
Please support our C++ advertiser: Programming Forums
Views: 2028 | Replies: 1
Reply
Join Date: Aug 2004
Posts: 5
Reputation: mrb260478 is an unknown quantity at this point 
Rep Power: 0
Solved Threads: 0
mrb260478 mrb260478 is offline Offline
Newbie Poster

Read integers from a file

  #1  
Nov 5th, 2007
Can some one help me to :

How to Read integers stored in a text file in the following format :

26 52 23 41 19 61 54 4 19 95 84 25 55 22
(integers delimted by a space.)

to be used for sorting later.

Have tried following code:

#include <stdio.h>
#include <conio.h>

void main()
{
FILE *fp;
int *x,i=0;
int a,b;

fp=fopen("file1.txt","r");
if (fp==NULL)
{
printf("File Cannot be opened.\n");
}
fseek(fp,0L,2);
a=ftell(fp);
rewind(fp);
fseek(fp,+1,0);
b=ftell(fp);
while (b<a)
{
fscanf(fp," %d ",x[i]);
printf ("%2d - %d\n",i,x[i]);
++i;
b=ftell(fp);
//printf("ftell = %d y = %d\n",b,a);
}
fclose(fp);


}

Output (which is wrong, which is obvious):

0 - 1735
1 - 11552
2 - 12576
3 - 13111
4 - 2613
5 - 12576
6 - 11552
7 - 12576
8 - 13617
9 - 12853
10 - 8202
11 - 8242
12 - 8237
13 - 12849

Please help.

Manish
AddThis Social Bookmark Button
Reply With Quote  
Join Date: Sep 2004
Posts: 6,515
Reputation: Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of Narue has much to be proud of 
Rep Power: 31
Solved Threads: 489
Super Moderator
Narue's Avatar
Narue Narue is offline Offline
Expert Meanie

Re: Read integers from a file

  #2  
Nov 5th, 2007
Rule 1) A pointer isn't an array. Just because you say int *x doesn't mean you can immediately use x as if it were an array. You need to allocate memory to it first.

Rule 2) main returns int.

Rule 3) Don't try to use the file positioning functions until you actually know what you're doing. Just read from the file and everything will work.

It's really as simple as this:
  1. #include <stdio.h>
  2.  
  3. int main ( void )
  4. {
  5. FILE *in;
  6. int list[50];
  7. int i;
  8.  
  9. in = fopen ( "file1.txt", "r" );
  10.  
  11. if ( in != NULL ) {
  12. for ( i = 0; i < 50; i++ ) {
  13. if ( fscanf ( in, "%d", list[i] ) != 1 )
  14. break;
  15. }
  16.  
  17. for ( j = 0; j < i; j++ )
  18. printf ( "%d - %d\n", j, list[j] );
  19.  
  20. fclose ( in );
  21. }
  22.  
  23. return 0;
  24. }
If you want the list to grow indefinitely to meet the contents of the file, you have no choice but to allocate and resize the memory for a pointer manually (assuming you really are using C even though you posted in the C++ forum).
I'm here to prove you wrong.
Reply With Quote  
Reply

Only community members can participate in forum threads. You must register or log in to contribute.

DaniWeb C++ Marketplace
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

 

Thread Tools Display Modes

Similar Threads
Other Threads in the C++ Forum

All times are GMT -4. The time now is 6:31 am.
Forum system based on vBulletin Copyright ©2000 - 2008, Jelsoft Enterprises Ltd.
©2003 - 2008 DaniWeb® LLC