第 15 章 位操作（dualview）

/*-----------------------------------
    dualview.c -- 位字段和按位运算符
-----------------------------------*/

#include <stdio.h>
#include <limits.h>

//边框线样式
#define SOLID    0
#define    DOTTED    1
#define DASHED    2

//三原色
#define BLUE    4
#define GREEN    2
#define RED        1

//混合颜色
#define BLACK    (RED & GREEN & BLUE)
#define YELLOW    (RED | GREEN)
#define MAGENTA    (RED | BLUE)
#define CYAN    (GREEN | BLUE)
#define WHITE    (RED | BLUE | GREEN)

//按位方法中用到的符号常量
#define OPAQUE        0x1
#define FILL_BLUE    0x8
#define FILL_GREEN    0x4
#define FILL_RED    0x2
#define FILL_MASK    0xE        //掩码
#define BORDER            0x100
#define BORDER_BLUE        0x800
#define BORDER_GREEN    0x400
#define BORDER_RED        0x200
#define BORDER_MASK        0xE00
#define B_SOLID            0
#define B_DOTTED        0x1000
#define B_DASHED        0x2000
#define STYLE_MASK        0x3000

struct box_props
{
    unsigned int opaque            : 1;
    unsigned int fill_color        : 3;
    unsigned int                : 4;
    unsigned int show_border    : 1;
    unsigned int border_color    : 3;
    unsigned int border_style    : 2;
    unsigned int                : 2;
};

//把数据看作结构或 unsigned short 类型的变量
union Views
{
    struct box_props st_view;
    unsigned short us_view;
};

const char *color[8] = 
{
    "black", "red", "green", "yellow", "blue", "magenta", "cyan", "white"
};

void show_settings(const struct box_props *pb);
void show_setting1(unsigned short);
char* itobs(int n, char *ps);
void show_bstr(const char *str);

int main()
{
    printf("size of struct box_props is %d bit
", CHAR_BIT * sizeof(struct box_props));
    printf("size of unsigned short is %d bit
", CHAR_BIT * sizeof(unsigned short));

    //创建 Vies 联合，并初始化 initialize struct box view
    union Views box = {{true, YELLOW, true, GREEN, DASHED}};
    char bin_str[8 * sizeof(unsigned int) + 1];

    printf("
Original box settings:
");
    show_settings(&box.st_view);
    printf("
Box settings using unsigned int view:
");
    show_setting1(box.us_view);
    //printf("bits are %s
", itobs(box.us_view, bin_str));
    printf("bits are:
");
    show_bstr(itobs(box.us_view, bin_str));
    
    box.us_view &= ~FILL_MASK;        //把表示填充色的位清零
    box.us_view |= CYAN;            //重置填充色
    box.us_view ^= OPAQUE;            //切换透明位
    box.us_view &= ~BORDER_MASK;    //边框颜色位清零
    box.us_view |= BORDER_RED;
    box.us_view &= ~STYLE_MASK;        //样式位清零
    box.us_view |= B_DOTTED;        //边框样式设置为点
    printf("
Modified box settings:
");
    show_settings(&box.st_view);
    printf("
Box settings using unsigned int view:
");
    show_setting1(box.us_view);
    //printf("bits are %s
", itobs(box.us_view, bin_str));
    printf("bits are:
");
    show_bstr(itobs(box.us_view, bin_str));

    return 0;
}

void show_settings(const struct box_props *pb)
{
    printf("Box is %s.
", pb->opaque ? "opaque" : "transparent");
    printf("The fill color is %s.
", color[pb->fill_color]);
    printf("Border %s.
", pb->show_border ? "shown" : "not shown");
    printf("The border color is %s.
", color[pb->border_color]);
    
    printf("The border style is ");
    switch (pb->border_style)
    {
    case SOLID:
        printf("solid.
");
        break;

    case DOTTED:
        printf("dotted.
");
        break;

    case DASHED:
        printf("dashed.
");
        break;

    default:
        printf("unknown type.
");
        break;
    }
}

void show_setting1(unsigned short us)
{
    printf("Box is %s.
", (us & OPAQUE) ? "opaque" : "transparent");
    printf("The fill color is %s.
", color[(us >> 1) & 0x07]);
    printf("Border %s.
", (us & BORDER) == BORDER ? "shown" : "not shown");
    printf("The border color is %s.
", color[us >> 9 & 0x07]);

    printf("The border style is ");
    switch (us & STYLE_MASK)
    {
    case B_SOLID:
        printf("solid.
");
        break;

    case B_DOTTED:
        printf("dotted.
");
        break;

    case B_DASHED:
        printf("dashed.
");
        break;

    default:
        printf("unknown style");
        break;
    }
}

char* itobs(int n, char *ps)
{
    const static int size = CHAR_BIT * sizeof(int);

    for (int i(size - 1); i >= 0; --i, n >>= 1)
        ps[i] = (01 & n) + '0';

    ps[size] = '';

    return ps;
}

//以 4 位为一组，显示二进制字符串
void show_bstr(const char *str)
{
    int i = 0;

    while (str[i])        //str[i] 不是空字符
    {
        putchar(str[i]);

        if (++i % 4 == 0 && str[i])
            putchar(' ');
    }

    putchar('
');
}