Binary file input, and reallocating

Im trying to read in integers from a binary file and then if its more than my capacity (cap) then it reallocates. but for some reason it's only printing 1 number. Here is my code and output.

Code:

#include<stdio.h>
#include<stdlib.h>

int main()
{
        int cap = 10;
        int *arr = malloc( sizeof(int) * cap);
        int i;
        int num_items = 0;
        FILE * fptr;

        fptr = fopen("pewp.dat", "r");

        num_items = fread ( arr, sizeof(int), cap, fptr);

        while(num_items == cap)
        {
                cap+=10;
                arr = realloc(arr, sizeof(int) * cap);
                num_items = fread ( arr, sizeof( int ), cap, fptr );
                printf("num_items = %d\n", num_items);
        }

        fclose( fptr );
        printf("array = ");
        for( i=0; i<num_items; ++i)
        {
                printf("%d ", arr[i]);
        }
        printf("\n");

        free ( arr );
        return 0;

}

output

Code:

num_items = 1
array = 0

Apparently its only reading one record in successfully.

Also the realloc is a little flawed, you are basically reading in 10 records, then expanding the buffer to 20 and reading in 20 more records which would in fact require a buffer of 30 records at that point (10 for the prior and 20 for the next) and so on...I assume you probably only want to read 10 new records each time and append those to the existing array, right? That's not happening now.

Can you please tell me how many integer is there in the file "pewp.dat" ?

here is my write for pewp.dat

Code:

#include <stdio.h>
#include <stdlib.h>

int main ()
{
    int arr[] = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };
    FILE * fptr = fopen ( "pewp.dat", "w" );

    fwrite ( arr, sizeof ( int ), 11, fptr );

    fclose ( fptr );
    return 0;
}

Originally Posted by nonpuz

I assume you probably only want to read 10 new records each time and append those to the existing array, right?

and yes i want to increment my array thats supposed to be taking in the number by ten each time.

You are having 11 elements , at the first read itself you got 10 elements , for the second fread you have remaining one element thats why you got num_items as 1. if you want the num_items as 11. then add the previous value of the num_elements

Code:

 num_items = num_items+ fread ( arr, sizeof( int ), cap, fptr );
                printf("num_items = %d\n", num_items);

Your whole code

Code:

#include<stdio.h>
#include<stdlib.h>

int main()
{
        int cap = 10;
        int *arr = malloc( sizeof(int) * cap);
        int i;
        int num_items = 0;
        FILE * fptr;

        fptr = fopen("pewp.dat", "r");

        num_items = fread ( arr, sizeof(int), cap, fptr);
                printf("verify num_items = %d\n", num_items);  // print for the verification 
                //exit(0);

        while(num_items == cap)
        {
                cap+=10;
                arr = realloc(arr, sizeof(int) * cap);
                num_items = num_items+ fread ( arr, sizeof( int ), cap, fptr );
                printf("num_items = %d\n", num_items);
        }

        fclose( fptr );
        printf("array = ");
        for( i=0; i<num_items; ++i)
        {
                printf("%d ", arr[i]);
        }
        printf("\n");

        free ( arr );
        return 0;

}

Output:

Code:

verify num_items = 10
num_items = 11
array = 0 9 8 7 6 5 4 3 2 1 0

that worked on making num_items = 11 but my array is printing 0 9 8 7 6 5 4 3 2 1 0 and i want it should be 10 9 8 .... 1 0

sine arr is a pointer it was re-writed by the second fread function , so we must write after giving some space

Code:

                num_items = num_items+ fread ( arr+num_items, sizeof( int ), cap, fptr );

Changed code

Code:

int main()
{
        int cap = 10;
        int *arr = malloc( sizeof(int) * cap);
        int i;
        int num_items = 0;
        FILE * fptr;

        fptr = fopen("pewp.dat", "r");

        num_items = fread ( arr, sizeof(int), cap, fptr);
                printf("verify num_items = %d\n", num_items);
                //exit(0);

        while(num_items == cap)
        {
                cap+=10;
                arr = realloc(arr, sizeof(int) * cap);
                num_items = num_items+ fread ( arr+num_items, sizeof( int ), cap, fptr ); // added num_items with arr
                printf("num_items = %d\n", num_items);
        }

        fclose( fptr );
        printf("array = ");
        for( i=0; i<num_items; ++i)
        {
                printf(">%d<\n", arr[i]);
        }
        printf("\n");

        free ( arr );
        return 0;

}

output

Code:

>< has no special meaning , just to distinguish 
verify num_items = 10
num_items = 11
array = >10<
>9<
>8<
>7<
>6<
>5<
>4<
>3<
>2<
>1<
>0<

Thanks a lot, works noa