// filescreate.c: Create files wich contain simply their file name.
// This program tries to create all file names of length n, wich is the first argument.
// All file names without "\0" and "/" are valid under Unix/Linux/... and are no problem 
// (for the kernel; the filesystem may have additional restrictions).
// So with n=1 it creates 254, for n=2 64,516, for n=3 16,387,064, ... files, in the actual directory.
// For many files you should use a file system with tail packing (e. g. reiserfs) to avoid 
// > 99,9 % wasted space.
// Usefull for testing correct handling for filenames, e. g. for demonstrating
// that handling filenames as a name wich ist terminated by a newline is generally a bad
// idea, because a file can have many non-printable characters like newlines in it's name.
// This program can not create files with a slash ("/") or zero byte ("\0") in it, because
// the kernel does not allow it, and it will produce error messages (Can not open file ...).
// Existing common files will generally be overwritten, but the program terminates with 
// SIGSEGV when the permission is not sufficient or when the file is a directory.
// So it's a good idea to start this program only as a test user, which has no access
// to important files.
// Version 1.0, 2009-06-01 Dr. Rolf Freitag, License: GPL version 3

#include <stdio.h>
#include <stdlib.h>
#include <iso646.h>             // for and, bitand, or, bitor ...

// simple version number
#define SOFTWARE_VERSION_NUMBER 1.0

int
main (const int argc, const char *const argv[])
{
  FILE *filea = NULL;
  int i = 0, j = 0, i_number = 0;
  char a_fa[123] = { '\0' };    // for file name

  // check the argument count (only one option)
  if (2 not_eq argc)                 
  {
    (void) fprintf (stdout, "%s version %.1f\n", argv[0], SOFTWARE_VERSION_NUMBER);
    (void) fprintf (stdout, "With one argument (n) this program produces all possible file names of length n and with their file name as their content.\n");
   exit (-1);
  }

  // read the number 
  if (argc == 2)                // second argument: number for file length
  {
    i_number = (int) strtol(argv[1], (char **)NULL, 0); 
  }
  // limit the number to 1..10 (no file bombing)
  if (i_number < 1)
    i_number = 1;
  if (i_number > 8)
    i_number = 8; // with 8: all possible file names of length 8; should be enough.

  for (i = 0; i < ( 1 << (i_number*8)); i++) // for all file names
  {
    // get the file name (=file content)
    for (j = 0; j < i_number; j++) // for all bytes of the file name
      a_fa[j] = ( i bitand (0xff << (j*8)) ) >> (j*8);

    // zero termination of the file name
    a_fa[j] = 0;

    // open, write and close the file
    if (NULL == (filea = fopen (a_fa, "wr")))
    {
      printf ("fopen failed for i=%d, file name %s\n", i, a_fa);
      continue;
    }
    (void) fprintf (filea, "%s", a_fa);
    (void) fclose (filea);
  } // for all file names

  exit (0);
} // main