Reading combinations of string and integer from file in C

Question

I am novice to C langugage, so please bear with me. I've tried to read a file which contains strings but output obtained is single character.

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>

#define CALLOC(num, type) ((char*)calloc (num, sizeof(char)))
#define FREE(addr) (free((void*) (addr)))

int i, count;
char *x, *y, *z;

int main (void) 

{

FILE *stream;
if ( (stream = fopen ( "test.txt", "r" )) == NULL )
{ printf ("Cannot read the new file\n");
exit (1);
}

count = 3;

x=CALLOC(count, char);
y=CALLOC(count, char);
z=CALLOC(count, char);


for ( i=0; i<count; i++ ) 
{ fscanf (stream,"%c %c %c", &x[i], &y[i], &z[i]);
printf ("\n %d %c %c %c ", i, x[i], y[i], z[i]);
}

FREE(x);
FREE(y);
FREE(z);

fclose (stream);

}

Input test.txt file contains

1 ab 1
2 aa 5
1 cc 1

current output

 0 1 a b
 1   1 2
 2   a a

Expected output

 0 1 ab 1
 1 2 aa 5
 2 1 cc 1

I doubt whether I should use a character array but it seems not working and I feel reading a int using char is acceptable. Here I require the expected output, for this any method/suggestion is appreciated.

really shouldnt be casting the pointer to free ( its pointless ). also no need to cast the calloc. and should move the global variables into main ( theres no need for them to be global ) — amdixon
– amdixon, Commented Jul 21, 2015 at 10:41

P.P · Accepted Answer · 2015-07-21 10:43:57Z

3

%c reads in only one char. So it's not going to read ab as a single char. Your lines in file and your formats don't correctly to read an entire line.

A simple approach is to use fgets() and print the entire line:

char line[256];
i = 0;

while(fgets(line, sizeof line, stream))
{
   printf ("%d %s", i, line);
   i++;
}

By the way, macros for calloc and free are unnecessary. They really don't make the code any easier to read than directly using those functions.

And the casts in them are also unnecessary.

answered Jul 21, 2015 at 10:43

P.P

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5 Comments

Emman Over a year ago

It is printing as expected but it no more stores the values in any variable (such as x,y or z) that I can access later, I am trying to access only the second column ie "ab, aa, cc" is there any way to obtain?

P.P Over a year ago

If you need to look at values, then use sscanf() on line. But you have to use %s read strings such as ab and ensure the buffer you have can store as many bytes.

phuclv Over a year ago

It's not only unneccessary but also not recommended stackoverflow.com/q/605845/995714 I've never seen any one uses free with cast

P.P Over a year ago

@LưuVĩnhPhúc I have seen it before. But I don't recommend it in my answers/comments due to its exaggeration, authoritative-sounding and inflammatory nature. Instead I would always link to comp.lang.c (linked in the answer) page which explains quite clearly about the effects of casting without missing any necessary detail. Casting free is a pre-standard artifact where free used to take a char*. I have seen it old code. Still some (incorrectly) do it out of habit.

Emman Over a year ago

@BlueMoon as per the inputs I have removed the unnecessary casting and free. Since I am coding for a bigger puzzle I have used global variables so that I can access as and when required now I've used "sscanf(buffer, "%d%s%d", &line, hex, &ch);" and found working thanks.

Dienes László · Accepted Answer · 2015-07-21 11:02:28Z

0

The problem is you have the scan file. %c read a 8bit value. You scanned 3 char, but the file is contain 4 characters. If you don't use to be the value of the x, y, z I don't understand why use malloc.

Here a working source:

#include <stdio.h>
#include <stdlib.h>

int main() {
  int count,i;
  char w,x,y,z;
  FILE *stream;
  if((stream = fopen("test.txt","r")) == NULL) {
    printf("Cannot read the new file\n");
    return 1;
  }
  count = 3;
  for(i=0;i<count;++i) {
    fscanf(stream,"%c %c%c %c\n",&w,&x,&y,&z);
    printf("%d %c %c%c %c\n",i,w,x,y,z);
  }
  return 0;
}

answered Jul 21, 2015 at 11:02

Dienes László

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Comments

ameyCU · Accepted Answer · 2015-07-21 11:44:32Z

0

for ( i=0;i<count; i++ ) 
        { 
            fscanf (stream,"%s %s %s", x, y, z);
            printf ("\n %d %s %s %s ", i, x, y, z);  
        }

You can modify your loop to this.This loop will read file until end of file and you have to use %s as ab is a string not charater so it can't be stored in a char variable.

edited Jul 21, 2015 at 11:44

answered Jul 21, 2015 at 11:04

ameyCU

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2 Comments

anatolyg Over a year ago

feof here is not used correctly; see explanations here

ameyCU Over a year ago

@anatolyg Yes ,thank you for correcting me . I modified the loop as per OP's need .

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