C //练习 8-2 用字段代替显式的按位操作，重写fopen和_fillbuf函数。比较相应代码的长度和执行速度。

C程序设计语言 （第二版） 练习 8-2

练习 8-2 用字段代替显式的按位操作，重写fopen和_fillbuf函数。比较相应代码的长度和执行速度。

注意：代码在win32控制台运行，在不同的IDE环境下，有部分可能需要变更。

IDE工具：Visual Studio 2010

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代码块：

#include <fcntl.h>
#include <stdarg.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/syscall.h>

#ifdef NULL
#undef NULL
#endif

#define NULL 0
#define EOF (-1)
#define BUFSIZ 1024
#define OPEN_MAX 20
#define SEEK_SET 0
#define SEEK_CUR 1
#define SEEK_END 2

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 = 03,
    _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)

#define PERMS 0666

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++;
}

int _flushbuf(int c, FILE *f) {
    int num_written, bufsize;
    unsigned char uc = c;

    if ((f->flag & (_WRITE | _EOF | _ERR)) != _WRITE) {
        return EOF;
    }

    if (f->base == NULL && ((f->flag & _UNBUF) == 0)) {
        if ((f->base = (char*)malloc(BUFSIZ)) == NULL)
            f->flag |= _UNBUF;
        else {
            f->ptr = f->base;
            f->cnt = BUFSIZ - 1;
        }
    }

    if(f->flag & _UNBUF){
        f->ptr = f->base = NULL;
        f->cnt = 0;
        if (c == EOF) {
            return EOF;
        }
        num_written = write(f->fd, &uc, 1);
        bufsize = 1;
    }
	else{
        bufsize = (int)(f->ptr - f->base);
        num_written = write(f->fd, f->base, bufsize);
        f->ptr = f->base;
        f->cnt = BUFSIZ - 1;
    }

    if (num_written == bufsize)
        return c;
    else {
        f->flag |= _ERR;
        return EOF;
    }
}

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 flushbuf(int c, FILE *f) {
    int num_written, bufsize;
    unsigned char uc = c;

    if ((f->flag & (_WRITE|_EOF|_ERR)) != _WRITE)
        return EOF;
    if (f->base == NULL && ((f->flag & _UNBUF) == 0)) {
        if ((f->base = (char*)malloc(BUFSIZ)) == NULL)
            f->flag |= _UNBUF;
        else {
            f->ptr = f->base;
            f->cnt = BUFSIZ - 1;
        }
    }
    if (f->flag & _UNBUF) {
        f->ptr = f->base = NULL;
        f->cnt = 0;
        if (c == EOF)
            return EOF;
        num_written = write(f->fd, &uc, 1);
        bufsize = 1;
    }
	else{
        if (c != EOF)
            *f->ptr++ = uc;
        bufsize = (int)(f->ptr - f->base);
        num_written = write(f->fd, f->base, bufsize);
        f->ptr = f->base;
        f->cnt = BUFSIZ - 1;
    }
    if(num_written == bufsize)
        return c;
    else{
        f->flag |= _ERR;
        return EOF;
    }
}

int fflush(FILE *f) {
    int retval;
    int i;

    retval = 0;
    if (f == NULL) {
        for (i = 0; i < OPEN_MAX; i++) {
            if ((_iob[i].flag & _WRITE) && (fflush(&_iob[i]) == -1))
                retval = -1;
        }
    } else {
        if ((f->flag & _WRITE) == 0)
            return -1;
        _flushbuf(EOF, f);
        if (f->flag & _ERR)
            retval = -1;
    }
    return retval;
}

int fclose(FILE *f) {
    int fd;

    if (f == NULL)
        return -1;
    fd = f->fd;
    fflush(f);
    f->cnt = 0;
    f->ptr = NULL;
    if (f->base != NULL)
        free(f->base);
    f->base = NULL;
    f->flag = 0;
    f->fd = -1;
    return close(fd);
}

int fseek(FILE *f, long offset, int whence) {
    int result;

    if ((f->flag & _UNBUF) == 0 && f->base != NULL) {
        if (f->flag & _WRITE) {
            if (fflush(f))
                return EOF;
        } else if (f->flag & _READ) {
            if (whence == SEEK_CUR) {
                if (offset >= 0 && offset <= f->cnt) {
                    f->cnt -= offset;
                    f->ptr += offset;
                    f->flag &= ~_EOF;
                    return 0;
                } else
                    offset -= f->cnt;
            }
            f->cnt = 0;
            f->ptr = f->base;
        }
    }
    result = (lseek(f->fd, offset, whence) < 0);
    if (result == 0)
        f->flag &= ~_EOF;
    return result;
}

int main(){
    int c;
    while((c = getchar()) != 'x'){
        putchar(c);
    }

	system("pause");
	return 0;
}