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            : ;
     unsigned int fill_color        : ;
     unsigned int                : ;
     unsigned int show_border    : ;
     unsigned int border_color    : ;
     unsigned int border_style    : ;
     unsigned int                : ;
 };

 //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[] =
 {
     "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\n", CHAR_BIT * sizeof(struct box_props));
     printf("size of unsigned short is %d bit\n", 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[ * sizeof(unsigned int) + ];

     printf("\nOriginal box settings:\n");
     show_settings(&box.st_view);
     printf("\nBox settings using unsigned int view:\n");
     show_setting1(box.us_view);
     //printf("bits are %s\n", itobs(box.us_view, bin_str));
     printf("bits are:\n");
     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("\nModified box settings:\n");
     show_settings(&box.st_view);
     printf("\nBox settings using unsigned int view:\n");
     show_setting1(box.us_view);
     //printf("bits are %s\n", itobs(box.us_view, bin_str));
     printf("bits are:\n");
     show_bstr(itobs(box.us_view, bin_str));

     return ;
 }

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

     printf("The border style is ");
     switch (pb->border_style)
     {
     case SOLID:
         printf("solid.\n");
         break;

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

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

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

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

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

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

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

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

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

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

     ps[size] = '\0';

     return ps;
 }

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

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

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

     putchar('\n');
 }

dualview.c