Thread: problem with reading ints from a text file into an array.

Hello everyone. I am having a problem with reading a textfile of ints into an array for sorting. The text file has the format of:

Code:

1
2
3
.
.
.

My main function is:

Code:

#include "header.h"

int main(void) {
    int i, array[SIZE];
    char buf[SIZE];

    FILE *fp;

    fp = fopen("100_sorted.txt", "r");
    if (fp ==NULL) {
        printf("Cannot open file for reading");
        exit(EXIT_FAILURE);
    }
    fgets(buf, sizeof(buf), fp);
    for (i = 0; i < SIZE; i++){
        sscanf(buf, "%d", &array[i]);
    }
    fclose(fp);

     insertion_sort(array,i);
     //selection_sort(array, n);
     //bubble_sort(array, n);
     //mod_bubble_sort(array, n);
     //quick_sort(array, 0, n - 1);
     //merge_sort(array, 0, n -1);

    for (i = 0; i < SIZE; i++){
        printf("%d\n", array[i]);
    }
    return (EXIT_SUCCESS);
}

The sort functions work correctly as I have tried them with a simple loop and array.

What is happening is it is seems to read the first int which is "1" and loops the "1" continously instead of reasing the next line.

I know it is probably something rather simple but I have been at it for a few hours and need a fresh set of eyes to take a looksee.

I would appreciate if someone could tell me what I need to do to fix it.
Thanks!

Let me go over your code, and show you exactly what is wrong.

Originally Posted by csharp100

Code:

        printf("Cannot open file for reading");

You forgot the newline at end of the line. Also, it would be better to write to standard error. That way, if the user redirected the expected output to a file, they will still see the error messages. So:

Code:

        fprintf(stderr, "Cannot open file for reading.\n");

That was not really an issue, but it is so useful in practice I thought I'd point it out anyway.

The real problems are in the following:

Originally Posted by csharp100

Code:

    fgets(buf, sizeof(buf), fp);
    for (i = 0; i < SIZE; i++){
        sscanf(buf, "%d", &array[i]);
    }

First, you are reading just one line, then parsing it again and again in the loop.

Second, you don't check the fgets() return value; it may return NULL if it cannot read the line.

Third, you don't check the sscanf() return value to see if it did the conversion or not.

I'd recommend you add a new variable, say char *line;, and moved the fgets() inside the loop:

Code:

        line = fgets(buf, sizeof buf, fp);
        if (!line) {
            fprintf(stderr, "Cannot read line %d.\n", i + 1);
            exit(EXIT_FAILURE);
        }

Similarly, to check that sscanf() really did do a conversion, check its return value -- the number of conversions you require from it:

Code:

        if (sscanf(line, "%d", &array[i]) < 1) {
            fprintf(stderr, "Line %d does not start with an integer.\n", i + 1);
            exit(EXIT_FAILURE);
        }

If you want to be thorough, you could also check the fclose() return value. You really should check it whenever you write to a file. It will return zero if there were no problems, and nonzero (EOF) if there is a problem. I'd recommend

Code:

    if (fclose(fp)) {
        fprintf(stderr, "Error closing the file.\n");
        exit(EXIT_FAILURE);
    }

Thank both of you. All was taken into consideration. It is functioning.