Reading in from a tab delimited text file?

selent · #1 25-Mar-2006, 07:23

Hi,

I have an assignment to do a minimum spanning tree. I've been given a text file such as the following:

York (tab) Leeds (tab) 60
London (tab) manchester (tab) 130

It's basically two cities and the distance between then, the text file therefore consits of three coloumns. I need to start my program by reading all of these values, but I don't know how to read them in since they're seperated by tabs. I'd really appriciate some help

Thank you,
Selen

davekw7x · #2 25-Mar-2006, 09:13

Quote:

Originally Posted by selent

Hi,

I have an assignment to do a minimum spanning tree.
.
.
.I don't know how to read them in since they're separated by tabs

If your assignment is a spanning tree, I would assume that you have had basic I/O. You might use fgets(), strtok(), sscanf() to get the data for each line.

Or you could just do it the old-fashioned way: do a little work, but maintain complete control.

The program specification will require that there be a tab character after the first city and a tab character after the second city. The program specification might also state the longest name that would be allowed. (How far is it from London to Llanfairpwllgwyngyllgogerychwyrndrobwllllantysilio gogogoch?)

If there is a bad input datum (no tab character, for example), you should probably specify what to do about this case also.

Here is one very elementary way to read the first name on the first line of the file:

Code:

1. Declare (or allocate) an array of char that is large enough to hold the longest
   name that would be allowed.

2. Open the input file.

3. Make a loop that starts with an index equal to zero and iterates
    the index to a maximum value of two less than the size of the
    array.

  Here is the loop:
     Read a character from the file
         If the character is a tab '\t' character
         then
            exit the loop
         else
            put the character into the next position of the name array

4. After the loop: put a zero byte (sometimes denoted '\0') into the
   next character in the array

CPP / C++ / C Code:

#include <stdio.h>

#define SIZE 30

int main()
{

  char city1[SIZE];

  int inchar;
  FILE *infile;
  char *inname = "test.txt";

  int i;

  infile = fopen(inname, "r");
  if (!infile) {
    printf("Couldn't open %s for reading\n");
    return 0;
  }

  for (i = 0; i < SIZE - 1; i++) {
    inchar = fgetc(infile);
    if (inchar == '\t') {
      printf("%d: tab encountered\n", i); /* print is for debug purposes only */
      break;
    }
    else {
      city1[i] = inchar;
    }
  }
  city1[i] = '\0';

  printf("city1: <%s>\n", city1);

  return 0;
}

I would probably test for EOF, and maybe '\n' inside the loop (and exit with an error message if either is encountered before the required '\t'). Maybe non-printing characters also. It's your call.

Regards,

Dave

cooper667 · #3 12-Apr-2006, 10:55

Quote:

Originally Posted by selent

Hi,

I have an assignment to do a minimum spanning tree. I've been given a text file such as the following:

York (tab) Leeds (tab) 60
London (tab) manchester (tab) 130

It's basically two cities and the distance between then, the text file therefore consits of three coloumns. I need to start my program by reading all of these values, but I don't know how to read them in since they're seperated by tabs. I'd really appriciate some help

Thank you,
Selen

Haha that looks familier...just starting mine...hope ive left enough time (unlike the predictive text)

mine reads in each line

Quote:

Return = fgets(City, 75, Cities);

then steps thro the line putting each char into an array untill a tab is reached

selent · #4 13-Apr-2006, 06:52

hahaha caught red-handed on a forum !! i've finished my MST now..just gonna finish the report today hopefully!
not sure who you are in electronics you are though, don't know the names of ppl very well

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Reading in from a tab delimited text file?

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