/* Compare to dbl.c. */

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

int chararray_append(char **a,int *aspace,int *alen,char c)
{
  if (*alen == *aspace) {
    int yspace = *aspace * 2 + 1;
    char *y = (char *) realloc(*a,yspace);
    if (!y) return 0;
    *a = y;
    *aspace = yspace;
  }
  (*a)[*alen] = c;
  ++*alen;
  return 1;
}

void die_read(void)
{
  fprintf(stderr,"file4: fatal: unable to read data.txt\n");
  exit(111);
}

int main(void)
{
  char *x = 0;
  int xspace = 0;
  int xlen = 0;
  FILE *f;
  char c;
  int i;

  f = fopen("data.txt","r");
  if (!f) die_read();

  while (fscanf(f,"%c",&c) == 1)
    if (!chararray_append(&x,&xspace,&xlen,c)) {
      fprintf(stderr,"file4: fatal: out of memory\n");
      exit(111);
    }
    
  if (ferror(f)) die_read();

  for (i = 0;i < xlen;++i) putchar(x[i]);
  for (i = 0;i < xlen;++i) putchar(x[i]);
  return 0;
}