The Empty Array In C

/*============================================================================
  ----------------------------------------------------------------------------
  nullArray.c - How to declare an array without stating its initial size and
                have the C compiler not complain about it.
                 (c) Damion 'Phr0z3n.Dev' Tapper, 2013.
                 Email: Phr0z3n.Dev@Gmail.com
  ----------------------------------------------------------------------------
  ============================================================================*/
#define USE_LEGAL_METHOD /* Comment this line to see the effect of the illegal method. */
#define USE_SEC_API /* Comment this line if you do not have the secure libraries. */

#define DONT_USE_CRASH_CODE /* Refer to the last #define (#ifndef) segment for use. */

#include <stdio.h>

int main(int argc, char *argv[], char **envp) /* char *envp[] is also valid but can be a memory hog. */
{
#ifndef USE_LEGAL_METHOD
    /* The compiler will complain about this... */
    char    nullArray[]; /* ...(the missing initial array size). */

    /* It will also complain about this. */
    struct tempS
    {
        char    nullArray[];
    };
#else
    /* But this is totally allowed. */
    struct tempS
    {
        int     structOffset; /* The magic bullet. */
        char    nullArray[];
    };
#endif

    struct tempS ts;

    ts.nullArray[0] = 'A';
    ts.nullArray[1] = 'B';
    ts.nullArray[100] = 'D';

#ifdef USE_SEC_API
    printf_s("%c\n", ts.nullArray[0]); /* The secure printf function (good programming practice). */
    printf_s("%c\n", ts.nullArray[1]);
    printf_s("%c\n", ts.nullArray[2]);
    printf_s("%c\n", ts.nullArray[100]);
    printf_s("%c\n", ts.nullArray[101]);
#else
    printf("%c\n", ts.nullArray[0]);
    printf("%c\n", ts.nullArray[1]);
    printf("%c\n", ts.nullArray[2]);
    printf("%c\n", ts.nullArray[100]);
    printf("%c\n", ts.nullArray[101]);
#endif


    /* What are the reasons for pointing this out?... */

    /* REASON #1: */
#ifndef DONT_USE_CRASH_CODE /* Comment the according #define at the top to see this segment at work. */
    /* In a pre-Service Pack version of Windows XP this piece of code would crash the system. */
    {
        int counter;

        for(counter = 0; counter >= 0; counter++)
            ts.nullArray[counter] = '\0';
    }
#endif

    /* REASON #2: */
    /* This nifty little trick could be used to exploit the main parameters char *argv[] and char **envp (*envp[]) */

    return 0;
}