C, Reading file elements into arrays, Bad Access Code

Question

I'm writing a program that reads in 30 numbers from a file stores them in an array then passes that array to a function which will print out only the even numbers from that array. However, I'm getting a Bad Access Code error in my while statement.

Any suggestions? Thanks in advance!

 #include <stdio.h>
void even(int numbers[]);

int main(int argc, const char * argv[]) {

    FILE *file = fopen("input.txt", "r");

    if (file == NULL) {
        printf("error");
    }

    int numbers[30];
    int num = 0;

    int i = 1;
    while(fscanf(file, "%d,", &num) > 0) {
        numbers[i] = num;
        i++;
    }

    fclose(file);

    even(numbers);

    return 0;
}

void even(int numbers[]){
    for (int i = 0; i < 30; i++) {
        if (numbers[i] %2 == 0) {
            printf("%d", numbers[i]);
        }
    }
}

while (fscanf(file, "%d, ", &num) > 0) is strictly wrong. Please read scanf(3). — Iharob Al Asimi
– Iharob Al Asimi, Commented Oct 23, 2015 at 17:13

Iharob Al Asimi · Accepted Answer · 2015-10-25 04:10:19Z

2

Your code has mainly 3.5 issues

You start with i = 1 in the first while loop.
```
int i = 1;
/*      ^ this should be 0 */
while(fscanf(file, "%d,", &num) > 0)
```
Since you start at 1 the 0th element is not initialized, yet you still try to read it (read before write) in even() and that, causes undefined behavior.
You never check for i's value not to go beyond the number of elements in the array.
You try to print 30 elements even though you might read less than that, you must count the total number of elements successfly read and pass that number to even(), or at least initialize the array to 0s.
If fscanf() succeeds it returns the number of elements matched. This will not cuase a problem in your code but is strictly wrong.

I suggets the following simple fix

int i = 0;
while ((fscanf(file, "%d,", &num) == 1) && (i < 30))

And

void even(int numbers[], size_t count) {
    for (int i = 0 ; i < count ; i++) {
        if (numbers[i] %2 == 0) {
            printf("%d", numbers[i]);
        }
    }
}

don't write a function that you can't reuse, it makes no sense.

edited Oct 25, 2015 at 4:10

answered Oct 23, 2015 at 17:14

Iharob Al Asimi

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1 Comment

bruceg Over a year ago

fscanf would return zero when your input file has unexpected characters.

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