Exercise 8.02

Page 178

Rewrite fopen and _fillbuf with fields instead of explicit bit operations. Compare code size and execution speed.

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

typedef struct _iobuf {
	int cnt; /* characters left */
	char *ptr; /* next character position */
	char *base; /* location of buffer */
	int flag; /* mode of file access */
	int fd; /* file descriptor */
} 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,
};

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)

#include <fcntl.h>
#define PERMS 0666
FILE *f_open(char *name, char *mode)
{
	int fd;
	FILE *fp;

	if (*mode != 'r' && *mode != 'w' && *mode != 'a') {
		return NULL;
	}

	/* Look for free space in _iob array */
	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);
		}
	} 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;
}

#include <stdlib.h>
#include <unistd.h>
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++;
}

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 main()
{
	/* This cannot be tested until _flushbuf and therefore getc are implemented, which 
	 * is the next task! Tested with a debugger instead. */
	int c;
	char str[100];
	for (int i = 0; (c = getchar()) != EOF; i++) {
		str[i] = c;
	}
}