How to count the number of integers in a file in C? [duplicate]

Question

I have this code which reads a file from the first argument to the main and counts the number of integers stored in it.

#include<stdio.h> #include <sys/wait.h> #include <stdlib.h> int array[100000]; int count = 0; int main(int argc, char* argv[]){ FILE* file; int i; file = fopen(argv[1],"r"); while(!feof(file)){ fscanf(file, "%d", &array[count]); count++; } for(i=0; i<count; i++){ printf(" \n a[%d] = %d\n",i,array[i]); } return 0; }

The output when I execute this file is

 a[0] = 1 a[1] = 2 a[2] = 3 a[3] = 4 a[4] = 5 a[5] = 6 a[6] = 7 a[7] = 8 a[8] = 9 a[9] = 10 a[10] = 0

Why is the value of count one greater than expected?

My input file using "./a.out /home/ghost/Desktop/file.txt" is as follows :

1 2 3 4 5 6 7 8 9 10

First mistake while(!feof(file)) that is wrong! You should read the documentation of fscanf() and then you would come up with this while (fscanf(file, "%d", array[count++]) == 1); Also, absolutetly no need for global variables. — Iharob Al Asimi
– Iharob Al Asimi, Commented Jan 12, 2016 at 13:41
You would have spotted/avoided this bug, if you bothered to check return value of fscanf (something you should always do). — hyde
– hyde, Commented Jan 12, 2016 at 13:43
@iharob Well, array is much safer as a global variable than a local variable in the stack, with that size... And using malloc in a snippet like this would just distract from the real issue. So using globals makes sense in the context. — hyde
– hyde, Commented Jan 12, 2016 at 13:51
@hyde I completely disagree. If the array is defined in main() it will have the same lifetime as the whole program. — Iharob Al Asimi
– Iharob Al Asimi, Commented Jan 12, 2016 at 13:53
@iharob I wasn't talking about lifetime, I was talking about stack size being limited. Allocating even just that maybe 5% (~400 KB out of typical 8MB) for the lifetime of the program is rather questionable. — hyde
– hyde, Commented Jan 12, 2016 at 14:00

Danny_ds · Accepted Answer · 2016-01-12 14:39:51Z

while(!feof(file)){ fscanf(file, "%d", &array[count]); count++; }

Instead of checking for eof, you need to check the returncode of fscanf():

while(fscanf(file, "%d", &array[count]) == 1) count++;

But it would be better to build in some safety too, like:

#define NUM_ITEMS 1000 int array[NUM_ITEMS]; int main(int argc, char* argv[]){ { FILE* file; int i, count = 0; file = fopen(argv[1], "r"); if (!file) { printf("Problem with opening file\n"); return 0; // or some error code } while(count < NUM_ITEMS && fscanf(file, "%d", &array[count]) == 1) count++; fclose(file); for(i=0; i<count; i++){ printf("a[%d] = %d\n", i, array[i]); } return 0; }

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