Realloc in C and NULL-pointer

Question

Why does this program not work for every input? (Read in input and print out in reverse order) Xcode6 generated the Error Message: hw5(14536,0x7fff7c23f310) malloc: * error for object 0x100103aa0: pointer being realloc'd was not allocated * set a breakpoint in malloc_error_break to debug Unfortunately I do not understand this.

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

int main()
{
  char *input;
  unsigned long long index;
  input = malloc(1);

  for (index = 0; (input[index] = getchar()) != EOF; index++)
  {
    if (input == NULL)
    {
      free(input);
      printf("Error: Out of memory!\n");
      return 0;
    }
    realloc(input, index + 2);
  }

  for (index = index - 1; index != 0; index--)
  {
    putchar(input[index]);
  }
  printf("\n");

  free(input);

  return 0;
}

Answer 1

realloc() returns a pointer to the new object. I'm using a temporary variable because if realloc() fails to reallocate the memory, a NULL is returned and input remains valid.

char* temp = realloc(input, index + 2);
if( !temp )
{
    //deal with error ...
}

input = temp ;