#include<fcntl.h>

#define PERMS 0666
#define  NULL  0
#define  EOF   (-1)
#define BUFSIZ 1024
#define  OPEN_MAX 20

typedef struct _iobuf
      {
   int cnt;
   char *ptr;
   char *base;
   int flag;
   int fd;
      }  FILE;

extern FILE _iob[OPEN_MAX];

#define stdin (&_iob[0])
#define stdout (&_iob[1])
#define stderr (&_iob[2])

enum flags
 {
  _READ  = 01,
  _WRITE = 02,
  _UNBUF = 04,
  _EOF   = 010,
  _ERR   = 020
 };


FILE _iob[OPEN_MAX] =
{
  { 0, (char *) 0, (char *) 0, _READ, 0},
  { 0, (char *) 0, (char *) 0, _WRITE, 1},
  { 0, (char *) 0, (char *) 0, _WRITE | _UNBUF, 2},
};


int _fillbuf(FILE *);
int _flushbuf(int, FILE *);

#define feof(p)      (((p)->flag & _EOF) != 0)      
#define ferror(p) (((p)->flag & _ERR) != 0)
#define fileno(p) ((p)->fd)
#define getc(p)      (--(p)->cnt >=0 ? (unsigned char) *(p)->ptr++ : _fillbuf(p))
#define putc(x,p) (--(p)->cnt >=0 ? *(p)->ptr++ = (x) : _flushbuf((x),p))
#define getchar()    getc(stdin) 
#define putchar(x)   putc((x), stdout)

FILE *fopen(char *name, char *mode);


int main(int argc, char **argv)
{
  FILE *fp1;
  int c;
  if (fp1=fopen(argv[1],"r")) putchar(getc(fp1));
  return 0;
}

FILE *fopen(char *name, char *mode)
 {
   int fd;
   FILE *fp;

  if (*mode != 'r' && *mode != 'w' && *mode != 'a') return NULL;
  for (fp = _iob; fp < _iob + OPEN_MAX; fp++)
    if ((fp->flag & (_READ | _WRITE)) == 0) break;
  if (fp >= _iob + OPEN_MAX) return NULL;

  if (*mode == 'w') fd = creat(name, PERMS);
  else if (*mode == 'a')
    {
       if ((fd = open(name, O_WRONLY, 0)) == -1)
         fd = creat(name, PERMS);
       lseek(fd, 0L, 2);
    }
  else
      fd = open(name, O_RDONLY, 0);

  if (fd == -1) return NULL;

  fp->fd = fd;
  fp->cnt = 0;
  fp->base = NULL;
  fp->flag = (*mode == 'r') ? _READ : _WRITE;
  return fp;
}

int _fillbuf(FILE *fp)
 {
   int bufsize;

   if ((fp->flag & (_READ | _EOF | _ERR)) != _READ) return EOF;
   bufsize = (fp->flag & _UNBUF) ? 1 : BUFSIZ;
   if (fp->base == NULL)
     if ((fp->base = (char *) malloc(bufsize)) == NULL) return EOF;
   fp->ptr = fp->base;
   fp->cnt = read(fp->fd, fp->ptr, bufsize);
   if (--fp->cnt < 0)
     {
       if (fp->cnt == -1)
         fp->flag |= _EOF;
       else
         fp->flag |= _ERR;
       fp->cnt = 0;
       return EOF;
     }
  return (unsigned char) *fp->ptr++;
 }