#define NULL 0
#define EOF (-1)
#define BUFSIZ 8196
#define OPEN_MAX 20 /* max #files open at once */

struct _flags {
     unsigned int is_read : 1;
     unsigned int is_write : 1;
     unsigned int is_unbuf : 1;
     unsigned int is_eof : 1;
     unsigned int is_err : 1;
};

typedef struct _iobuf {
     int cnt; /* characters left */
     char *ptr; /* next character position */
     char *base; /* location of buffer */
     struct _flags flags;
     int fd; /* file descriptor */
} FILE;

extern FILE _iob[OPEN_MAX];

#define stdin (&_iob[0])
#define stdout (&_iob[1])
#define stderr (&_iob[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 fflush(FILE *stream);
int fclose(FILE *stream);
int fseek(FILE *fp, long offset, int origin);