realloc does not copy values correctly

Question

I am trying to read a text file with unknown size into an array. I do that by reading one character at a time into the array and reallocate memory if the the end of the array is reached.

Starting from the increase in array size from 16 to 32, the realloc method copies only the first 4 characters.

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


int main()
{
    int *text_arr = malloc(1*sizeof(int));
    text_arr[0] = '\0';
    int text_len=1;
    int i=0;
    FILE *fp;

    fp = fopen("1.txt", "r");
    
    while ((text_arr[i] = fgetc(fp)) != EOF) {
        /* increment i for next loop */
        i++;

        /* extend the array if needed */
        if (i >= text_len) {
            /* debug prints */
            printf("Text: ");
            for (int n=0; n<i; n++)
                printf("%c,", text_arr[n]);
            printf("\n\n");
            
            /* double array size */
            text_len *= 2;
            text_arr = (int*)realloc(text_arr, text_len);
        }
    }
    text_arr[i] = '\0';

    fclose(fp);
    
    return 0;
}

What could be the problem?

Answer 1

You are working with sizeof (int) sized objects, you need to make sure to multiply your requested number of bytes by this size when you reallocate.

realloc(text_arr, sizeof (int) * text_len);