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Jun 23rd, 2005

Read in a file and store in char array

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I'm C newbie and i'm having a tough time with my first assignment

The assignment is on creating a Number Puzzle.....apparently it's the newest craze in Toronto and my prof is a big fan....unfortunately

I'm trying to read in a file which looks like this:
9,8, ,5,,4,,
7,3,1, ,5

this is what i want to do..
-Read in the file and use fscanf to store everything in an array of chars called tempGrid. (I don't want the extra white space between commas)
-then tempGrid to another 1D array pointed to by a pointer called *grid.....WITHOUT the commas.
-And just print out the result

Obviously this is not my whole assignment, only like 1% of it.
I've tried to do this simple thing for two days now and i can't seem to get it to work.
PLEASE HELP!!

Another question: does fscanf write the result straight to an array or do i have to pass in a pointer that points to an array?

Thanks for any help. I really appreciate it. I'm on the verge of tearing my hair out in frustration

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dile

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Jun 23rd, 2005

Re: Read in a file and store in char array

Post the code you have so far -- remember to use code tags: [code][/code].

Dave Sinkula

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Jun 23rd, 2005

Re: Read in a file and store in char array

this is what i have so far:

C Syntax (Toggle Plain Text)
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
 
int main(int argc, char *argv[])
{
	FILE *f_read;
	int num;
	char tempGrid[50];
	int i,t;
 
	char *grid;
 
	grid = (char *)malloc(sizeof(char) * 9 * 9);
 
	if (argv[1] != NULL){
		f_read = fopen(argv[1], "r");
            	while ((num = fscanf(f_read, "%c",tempGrid))!= EOF){
			for (i =0; i < 50; i++){							grid[i] = tempGrid[i];
			}
		}
	}
 
	for (t = 0; t <50; t++)
		printf("%c\n", grid[t]);
	}
	return(0);
}
#include <stdio.h>
#include <string.h>
#include <stdlib.h>


int main(int argc, char *argv[])
{
	FILE *f_read;
	int num;
	char tempGrid[50];
	int i,t;

	char *grid;

	grid = (char *)malloc(sizeof(char) * 9 * 9);

	if (argv[1] != NULL){
		f_read = fopen(argv[1], "r");
            	while ((num = fscanf(f_read, "%c",tempGrid))!= EOF){
			for (i =0; i < 50; i++){							grid[i] = tempGrid[i];
			}
		}
	}

	for (t = 0; t <50; t++)
		printf("%c\n", grid[t]);
	}
	return(0);
}

when i run it the characters the array stores is some other weird characters. I think i need to do some kind of conversion after the while loop before i store the chars.

dile

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Jun 23rd, 2005

Re: Read in a file and store in char array

In C, it may be better not to cast the return value of malloc.

C Syntax (Toggle Plain Text)
grid = (char *)malloc(sizeof(char) * 9 * 9);
grid = (char *)malloc(sizeof(char) * 9 * 9);

Checking the return value is always recommended. As is here.

C Syntax (Toggle Plain Text)
f_read = fopen(argv[1], "r");
f_read = fopen(argv[1], "r");

Checking return values will save you countless hours of debugging, so it's a good habit to start. Unless you like to pull your hair out for hours.

This line was missing a {.

C Syntax (Toggle Plain Text)
   for ( t = 0; t <50; t++ )
   for ( t = 0; t <50; t++ )

Here is a place to fix up:

C Syntax (Toggle Plain Text)
      while ( (num = fscanf(f_read, "%c", tempGrid))!= EOF )
      while ( (num = fscanf(f_read, "%c", tempGrid))!= EOF )

I might go with something more like this.

C Syntax (Toggle Plain Text)
for ( i = 0; i < 50 && fscanf(f_read, "%c", &tempGrid[i]) == 1; i++ )
for ( i = 0; i < 50 && fscanf(f_read, "%c", &tempGrid[i]) == 1; i++ )

You are only reading into the first element of tempGrd. Later you pretend you have filled the whole thing up.

(Toggle Plain Text)

grid[i] = tempGrid[i];

Multiplying by sizeof(char) is the long way of multiplying by one, which is pointless.

If the number of characters in the file may be less than your 50, it might be wise only to print out as many as were read.

Take another swing and we'll move forward from there.

Dave Sinkula

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Re: Read in a file and store in char array

C Syntax (Toggle Plain Text)
for ( i = 0; i < 50 && fscanf(f_read, "%c", &tempGrid[i]); i++ )
for ( i = 0; i < 50 && fscanf(f_read, "%c", &tempGrid[i]); i++ )

Could you explain that line a bit?
I don't really undestand how "i <50 && fscanf..." part works

And also the malloc line was given to us by the prof. He said that we have to use that exact line. He said it's his way of making sure we don't use a 2D array for the assignment :p

dile

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Jun 23rd, 2005

Re: Read in a file and store in char array

Quote originally posted by dile ...

C Syntax (Toggle Plain Text)
for ( i = 0; i < 50 && fscanf(f_read, "%c", &tempGrid[i]); i++ )
for ( i = 0; i < 50 && fscanf(f_read, "%c", &tempGrid[i]); i++ )
Could you explain that line a bit?
I don't really undestand how "i <50 && fscanf..." part works

It just has two conditions to continue the loop -- that you don't overflow the buffer and that you successfully read some data (in the edited and fixed version the return value of fscanf is compared to 1).

Quote originally posted by dile ...

And also the malloc line was given to us by the prof. He said that we have to use that exact line. He said it's his way of making sure we don't use a 2D array for the assignment :p

[sarcasm=thin]Great -- another professor who needs a few more lessons.[/sarcasm]

Dave Sinkula

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Re: Read in a file and store in char array

You seem engaged in this, so I'll post my working copy.

C Syntax (Toggle Plain Text)
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
 
int main(int argc, char *argv[])
{
   char *grid = malloc(9 * 9);
   if ( grid )
   {
      int t, i = 0;
      if ( argc > 1 )
      {
         FILE *f_read = fopen(argv[1], "r");
         if ( f_read )
         {
            char tempGrid[50];
            puts("Just before while");
            while ( i < 50 && fscanf(f_read, "%c", &tempGrid[i]) == 1 )
            {
               if ( tempGrid[i] != ',' && !isspace(tempGrid[i]) )
               {
                  grid[i] = tempGrid[i];
                  ++i;
               }
            }
         }
      }
      for ( t = 0; t < i; t++ )
      {
         printf("%c\n", grid[t]);
      }
      free(grid);
   }
   return 0;
}
 
/* my output
H:\test>test file.txt
Just before while
9
8
5
4
7
3
1
5
*/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

int main(int argc, char *argv[])
{
   char *grid = malloc(9 * 9);
   if ( grid )
   {
      int t, i = 0;
      if ( argc > 1 )
      {
         FILE *f_read = fopen(argv[1], "r");
         if ( f_read )
         {
            char tempGrid[50];
            puts("Just before while");
            while ( i < 50 && fscanf(f_read, "%c", &tempGrid[i]) == 1 )
            {
               if ( tempGrid[i] != ',' && !isspace(tempGrid[i]) )
               {
                  grid[i] = tempGrid[i];
                  ++i;
               }
            }
         }
      }
      for ( t = 0; t < i; t++ )
      {
         printf("%c\n", grid[t]);
      }
      free(grid);
   }
   return 0;
}

/* my output
H:\test>test file.txt
Just before while
9
8
5
4
7
3
1
5
*/

Last edited by Dave Sinkula; Jun 23rd, 2005 at 11:58 pm. Reason: Changed 'if ( argc > 1 && argv[1] != NULL )' to 'if ( argc > 1 )'.

Dave Sinkula

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Jun 24th, 2005

Re: Read in a file and store in char array

thank you so much for your help!

Now i can actually start on the assignment

dile

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Oct 9th, 2010

Re: Read in a file and store in char array

Sorry, i am newbie...i want to ask to dave, where the read file command in the code?

daffi_gusti

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