C copying a file into a structure

Question

Ok, so I have a file with integers, like:

and I want to copy it into my structure, the problem being that my structure has 2 columns, and I don't know how to copy the file into just one.

My question is: is there a quick and easy function like qsort that will automatically copy my file over?

 #include <stdio.h>      /* printf */
 #include <stdlib.h>     /* qsort */

struct Element
{
int userId;
int score;
};

struct Element elements[] = { 
{1, 13},
{2,  9},
{3, 13},
{4, 19},
{5,  8},
{6, 11},
{7, 14},
{8, 17},
};

int ascendingSortCompareFunction (const void * a, const void * b)
{
   return (((struct Element *)a)->score - ((struct Element *)b)->score);
}

int descendingSortCompareFunction (const void * a, const void * b)
{
   return ((struct Element *)b)->score) - (((struct Element *)a)->score;
}

int main ()
{
int n;
int count;

count = sizeof(elements) / sizeof(elements[0]);

qsort(elements, count, sizeof(elements[0]), ascendingSortCompareFunction);
printf ("UserID\tScore (Ascending Sort)\n");
for (n = 0 ; n < count ; n++)
    printf ("%d\t%d\n", elements[n].userId, elements[n].score);

qsort(elements, count, sizeof(elements[0]), descendingSortCompareFunction);
printf ("UserID\tScore (Descending Sort)\n");
for (n = 0 ; n < count ; n++)
    printf ("%d\t%d\n", elements[n].userId, elements[n].score);

getchar();

return 0;
}

Sorry, but what does qsort have to do with reading numbers from a file? Please clarify. — OldProgrammer, Jan 02 '15 at 16:39
I'm not sure if I got it right. You're trying to load the values that are in your file in the `userId` field of the `Element`s present in your `elements` array? — Richard-Degenne, Jan 02 '15 at 16:41
@OldProgrammer Nothing, I have no idea how to read the file to a structure. qsort is the next bit — The Blue Juice, Jan 02 '15 at 16:42
@RichouHunterc I'm trying to load the file into my second column — The Blue Juice, Jan 02 '15 at 16:43
http://stackoverflow.com/questions/20378430/reading-numbers-from-a-text-file-into-an-array-in-c — OldProgrammer, Jan 02 '15 at 16:43
To be picky: your structure doesn't have "columns". In fact your structure hold exactly two values. You have an array of this structure. And it seems that you want to load the file data in the first field of each element in the array. Using the correct terminology will help you find relevant information on your own. — Jonathon Reinhart, Jan 02 '15 at 17:11
@JonathonReinhart Noted, I guess I was just trying to get my point across — The Blue Juice, Jan 02 '15 at 17:19
Is it the first column or the second column you want? My answer was assuming the second which made more sense to me, but you tell me — Neil Neyman, Jan 02 '15 at 17:25

Neil Neyman · Answer 1 · 2015-01-02T17:22:47.633

1

Not sure if there's a function available but it doesn't take much code to do it manually.

You open the file:

FILE *fp;
fp = fopen("myfile.txt", "r")

Then loop and read the file one line at a time, and insert each int into the struct array:

//looping through file and array with i as a counter
fscanf(fp,"%d", &elements[i].score);

This assumes that you are reading the scores from your file. That hopefully is enough to get you started!

Oh, and close the file after:

fclose(fp);

edited Jan 02 '15 at 17:22

answered Jan 02 '15 at 16:58

Neil Neyman

2,116
16
21

Not to mention `struct Element elements[8]` – Gopi Jan 02 '15 at 17:00
3

it should be &elements[i].score, instead of elements[i].score – simon_xia Jan 02 '15 at 17:05

Iharob Al Asimi · Answer 2 · 2015-01-02T23:40:24.143

I am almost sure that this is what you are looking for

#include <stdio.h>      /* printf */
#include <stdlib.h>     /* qsort */

struct Element
{
    int userId;
    int score;
};

int ascendingSortCompareFunction (const void * a, const void * b)
{
   return (((struct Element *)a)->score - ((struct Element *)b)->score);
}

int descendingSortCompareFunction (const void * a, const void * b)
{
   return -ascendingSortCompareFunction(a, b);
}

void readFromFile(const char *const filename,  struct Element **elements, size_t *count)
{
    FILE *file;
    void *auxiliary;
    int   index;
    int   score;
    char  line[128];

    if ((elements == NULL) || (count == NULL))
        return;
    *count    = 0;
    *elements = NULL;
    file      = fopen(filename, "r");
    if (file == NULL)
        return;

    index = 0;
    while (fgets(line, sizeof(line), file) != NULL)
    {
        if (sscanf(line, "%d", &score) == 1)
        {
            auxiliary = realloc(*elements, (1 + *count) * sizeof(struct Element));
            if (auxiliary == NULL)
            {
                free(*elements);
                fclose(file);

                *elements = NULL;

                return;
            }
            *elements                  = auxiliary;
            (*elements)[*count].userId = 1 + index;
            (*elements)[*count].score  = score;

            *count += 1;
            index  += 1;
        }
    }
    fclose(file);
}

int main ()
{
    size_t          count;
    size_t          n;
    struct Element *elements;
    size_t          size;

    elements = NULL;
    size     = sizeof(struct Element);
    count    = 0;

    readFromFile("/home/iharob/file.txt", &elements, &count);
    if ((elements != NULL) && (count > 0))
    {
        qsort(elements, count, size, ascendingSortCompareFunction);
        printf ("UserID\tScore (Ascending Sort)\n");

        for (n = 0 ; n < count ; n++)
            printf ("%d\t%d\n", elements[n].userId, elements[n].score);

        qsort(elements, count, size, descendingSortCompareFunction);
        printf ("UserID\tScore (Descending Sort)\n");

        for (n = 0 ; n < count ; n++)
            printf ("%d\t%d\n", elements[n].userId, elements[n].score);

        free(elements);
    }
    getchar();

    return 0;
}

after this line: '*elements = NULL;' there needs to be a line: '*count = 0;' — user3629249, Jan 02 '15 at 23:04
@user3629249 wow that was a very stupid mistake. Although `count` is initialized in `main()` and hence there was no error, but it's better to initialize it in `readFromFile()`. — Iharob Al Asimi, Jan 02 '15 at 23:40

C copying a file into a structure

2 Answers2