Sorting array of data structures in C

Question

My program is supposed to read a file, store the records of this file and then sort every record. I'm using an insertion sort algorithm to sort the records, but i'm having some problems making it work.

For example, if the thext file looks like that

string one; string one; string one; 1
string two; string two; string two; 2
string three; stringh three; string three; 3

I need the third record to be the first, the second one to be the second, and the first one to be the last. Since 3>2>1.

I think that the Insertion Sort algorithm is right, since i tested it with a simple array and it's working, but i'm having an hard time implementing it into my program. The error i get is insertionSort’ makes pointer from integer without a cast, i think it's because i'm using a data structure to store the data scanned from the file.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXLEN 100

struct Element
   {
    char one[100];
    char two[100];
    char three[100];
    int st;
   };

void insertionSort(int arr[]);
void printArray(int arr[]);


int main() {


    int i;
    struct Element elements[MAXLEN];


    FILE * fpointer = fopen("clients.txt", "r");

    char buffer[1024]; // Define a really big string to hold the line of text in
    char *field;
    int field_number;


    while(fgets(buffer,1024,fpointer))
        {
        field_number=0;
        field=strtok(buffer,";");
        while(field)
          {
           switch(field_number)
            {
              case 0:
              strcpy(elements[i].one,field);
              break;
              case 1:
              strcpy(elements[i].two,field);
              break;
              case 2:
              strcpy(elements[i].three,field);
              break;
              case 3:
              elements[i].st=atoi(field);
              break;
            }
         field=strtok(NULL,";"); // Get next field
         field_number++;
         }
        i++; // Move the index for elements to the next one
      }


    insertionSort(elements[MAXLEN].st);
    printArray(elements[MAXLEN].st);

    fclose(fpointer);
    return 0;

}


void insertionSort(int arr[])
{  
   struct Element elements[MAXLEN];
   int i, key, j;
   for (i = 1; i < 10; i++)
    {
       key = elements[i].st;
       j = i-1;


       while (j >= 0 && elements[j].st > key)
       {
           elements[j+1].st = elements[j].st;
           j = j-1;
       }
       elements[j+1].st = key;
    }

}


void printArray(int arr[])
{
int i;
for (i=0; i < 10; i++) {
    printf("%d ", arr[i]);
    printf("\n");
  }
}

Possible duplicate of Sorting structures from a file alphabetically in C — Chris Turner
– Chris Turner, Commented Aug 31, 2018 at 15:46

kiran Biradar · Accepted Answer · 2018-08-31 16:18:59Z

1

You have following problems in your code.

you have declared void insertionSort(int arr[]); and void printArray(int arr[]); functions which takes pointer to int array as argument but you are passing insertionSort(elements[MAXLEN].st); & printArray(elements[MAXLEN].st); just int as parameter.

Also insertionSort will sort the st fields of struct Element elements[MAXLEN]; but not the elements itself and insertionSort will sort the array in ascending order not in descending order as you want.

Hence Change this

   while (j >= 0 && elements[j].st > key)

to

   while (j >= 0 && elements[j].st < key.st)

Consider below code as example.

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define MAXLEN 100

    struct Element
       {
        char one[100];
        char two[100];
        char three[100];
        int st;
       };

    void insertionSort(struct Element elements[]);
    void printArray(struct Element elements[]);


    int main() {


        int i;
        struct Element elements[MAXLEN];


        FILE * fpointer = fopen("clients.txt", "r");

        char buffer[1024]; // Define a really big string to hold the line of text in
        char *field;
        int field_number;


        while(fgets(buffer,1024,fpointer))
            {
            field_number=0;
            field=strtok(buffer,";");
            while(field)
              {
               switch(field_number)
                {
                  case 0:
                  strcpy(elements[i].one,field);
                  break;
                  case 1:
                  strcpy(elements[i].two,field);
                  break;
                  case 2:
                  strcpy(elements[i].three,field);
                  break;
                  case 3:
                  elements[i].st=atoi(field);
                  break;
                }
             field=strtok(NULL,";"); // Get next field
             field_number++;
             }
           i++; // Move the index for elements to the next one
          }


        insertionSort(elements);
        printArray(elements);

        fclose(fpointer);
        return 0;

    }


void insertionSort(struct Element elements[])
{
   int i, j;
  struct Element key;
   for (i = 1; i < 10; i++)
    {
       key = elements[i];
       j = i-1;


       while (j >= 0 && elements[j].st < key.st)
       {
           elements[j+1] = elements[j];
           j = j-1;
       }
       elements[j+1] = key;
    }

}


    void printArray(struct Element elements[])
    {
    int i;
    for (i=0; i < 3; i++) {
        printf("%s %s %s%d ", elements[i].one,elements[i].two,elements[i].three,elements[i].st);
        printf("\n");
      }
    }

edited Aug 31, 2018 at 16:18

answered Aug 31, 2018 at 15:54

kiran Biradar

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3 Comments

Jack022 Over a year ago

Basically i had to pass the struct, i did not understand that. Thank you a lot!

Chris Turner Over a year ago

That code only copies the number field of the struct, but leaves the strings in the wrong place

kiran Biradar Over a year ago

@ChrisTurner Indeed, fixed your findings.

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