File handling in c

Question

I made a simple program to read the no of values and then, those values from file and storing them in an array and print the values of array.

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

void main(){
    int i=0,j=0,n,no[n];
    FILE *fp=fopen("input.txt","r");
    if(fp==NULL)
        printf("File input error\n");
    else{
        fscanf(fp,"%d",&n);
        *no=(int *)malloc(n*sizeof(int));
        while(i<n){
            fscanf(fp,"%d",&no[i]);
            printf("%d\t",no[i]);
            i++;
        }
    }
}

My input file was as follows

10 37 21 55 52 68 97 02 00 103 84

and the output I got is

37 21 55 52 68 97 2 0

Why do I see this output?

change to int *no;.. no=(int *)malloc(n*sizeof(int));

BLUEPIXY
– BLUEPIXY

2015-06-11 18:16:47 +00:00
Commented Jun 11, 2015 at 18:16 — BLUEPIXY
– BLUEPIXY, Commented Jun 11, 2015 at 18:16
What output did you expect?

Fred Larson
– Fred Larson

2015-06-11 18:23:06 +00:00
Commented Jun 11, 2015 at 18:23 — Fred Larson
– Fred Larson, Commented Jun 11, 2015 at 18:23
All the numbers should be printed?

Neeraj Verma
– Neeraj Verma

2015-06-11 18:28:01 +00:00
Commented Jun 11, 2015 at 18:28 — Neeraj Verma
– Neeraj Verma, Commented Jun 11, 2015 at 18:28
Including the first one (10)?

Fred Larson
– Fred Larson

2015-06-11 18:28:39 +00:00
Commented Jun 11, 2015 at 18:28 — Fred Larson
– Fred Larson, Commented Jun 11, 2015 at 18:28
I want numbers stored in the array only.

Neeraj Verma
– Neeraj Verma

2015-06-11 18:33:59 +00:00
Commented Jun 11, 2015 at 18:33 — Neeraj Verma
– Neeraj Verma, Commented Jun 11, 2015 at 18:33

R Sahu · Accepted Answer · 2015-06-11 18:22:18Z

2

The line

    *no=(int *)malloc(n*sizeof(int));

is not right. I am surprised your compiler didn't warn you.

*no is of type int. You are assigning a pointer to an int.

Using gcc, I get the following warning.

soc.c: In function ‘main’:
soc.c:11:12: warning: assignment makes integer from pointer without a cast
         *no=(int *)malloc(n*sizeof(int));

Also, the line

int i=0,j=0,n,no[n];

is not correct. n is not initialized before being used to define no.

Here's an updated version of your program that should work.

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

void main(){
   int i=0,j=0,n;
   int* no;
   FILE *fp=fopen("input.txt","r");
   if(fp==NULL)
      printf("File input error\n");
   else{
      if ( fscanf(fp,"%d",&n) == 1 )
      {
         no = malloc(n*sizeof(int));
         while(i<n){
            if ( fscanf(fp,"%d", &no[i]) == 1 )
            {
               printf("%d\t",no[i]);
            }
            else
            {
               // Unable to read the number.
               // Get out of the loop.
               break;
            }
            i++;
         }
      }
      else
      {
         // Unable to read n.
         // Print some message to indicate the error
      }
   }
}

answered Jun 11, 2015 at 18:22

R Sahu

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5 Comments

Neeraj Verma Over a year ago

what does 'no' signify here?

R Sahu Over a year ago

@NeerajVerma, no is a variable of type int*. No relation with the English word "no".

Neeraj Verma Over a year ago

Dude! I made this program and I know what is no .

Neeraj Verma Over a year ago

I am asking for malloc allocation of this variable

R Sahu Over a year ago

ok, which part of no = malloc(n*sizeof(int)); didn't make sense?

Tlacenka · Accepted Answer · 2015-06-11 18:14:15Z

0

In your code, you are trying to read n elements without checking for EOF. You should add a condition comparing fscanf with number of scanned elements (in this case 1) and therefore avoid reaching EOF unknowingly.

answered Jun 11, 2015 at 18:14

Tlacenka

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