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Read in a file and store in char array

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Join Date: Jun 2005

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dile

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Read in a file and store in char array

Jun 23rd, 2005

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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Join Date: Apr 2004

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: Read in a file and store in char array

Jun 23rd, 2005

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

"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand

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Join Date: Jun 2005

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dile

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Re: Read in a file and store in char array

Jun 23rd, 2005

this is what i have so far:

 Help with Code Tags 
 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.

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Join Date: Apr 2004

Posts: 4,342

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: Read in a file and store in char array

Jun 23rd, 2005

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

 Help with Code Tags 
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grid = (char *)malloc(sizeof(char) * 9 * 9);
grid = (char *)malloc(sizeof(char) * 9 * 9);

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

 Help with Code Tags 
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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 {.

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   for ( t = 0; t <50; t++ )
   for ( t = 0; t <50; t++ )

Here is a place to fix up:

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      while ( (num = fscanf(f_read, "%c", tempGrid))!= EOF )
      while ( (num = fscanf(f_read, "%c", tempGrid))!= EOF )

I might go with something more like this.

 Help with Code Tags 
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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.

Help with Code Tags

(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.

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Join Date: Jun 2005

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dile

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Re: Read in a file and store in char array

Jun 23rd, 2005

 Help with Code Tags 
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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

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: Read in a file and store in char array

Jun 23rd, 2005

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Originally Posted by dile

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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).

•

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]

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Join Date: Apr 2004

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: Read in a file and store in char array

Jun 23rd, 2005

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

 Help with Code Tags 
 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
*/