示例：位字段与位运算

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//提供CHAR_BIT的定义，CHAR_BIT表示每字节的位数
#include <limits.h>
//C99定义了bool、true、false
#include <stdbool.h>

/* 线的样式 */
#define SOLID 0  //实线
#define DOTTED 1 //点线
#define DASHED 2 //虚线

/* 三原色 */
#define BLUE 4
#define GREEN 2
#define RED 1
/* 混合色 */
#define BLACK 0
#define YELLOW (RED | GREEN)
#define MAGENTA (RED | BLUE)
#define CYAN (GREEN | BLUE)
#define WHITE (RED | GREEN | BLUE)

/* 按位方法中用到的符号常量 (也可以将下面的常量声明为枚举) */
#define OPAQUE 0x1
#define FILL_BLUE 0x8
#define FILL_GREEN 0x4
#define FILL_RED 0x2
#define FILL_MASK 0xE
#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

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

//声明一个描述方框属性的结构体
//注意：不同的机器，存储位字段的顺序不同。
struct box_props {
	bool opaque : 1; //是否透明; 或者 unsigned int (C99以前)
	unsigned int fill_color : 3;//填充色
	unsigned int : 4;
	bool show_border : 1;//是否显示边框; 或者 unsigned int (C99以前)
	unsigned int border_color : 3; //边框颜色
	unsigned int border_style : 2; //边框样式
	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;
};

void show_settings(const struct box_props * pb);
void show_settings1(unsigned short);
char * itobs(int n, char * ps);

int main(int argc, char* argv[])
{
	/* 创建Views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:\n");
	show_settings(&box.st_view);
	printf("\nBox settings using unsigned int view:\n");
	show_settings1(box.us_view);

	printf("bits are %s\n",
		itobs(box.us_view, bin_str));
	box.us_view &= ~FILL_MASK; /* 把表示填充色的位清0 */
	box.us_view |= (FILL_BLUE | FILL_GREEN); /* 重置填充色 */
	box.us_view ^= OPAQUE; /* 切换是否透明的位 */
	box.us_view |= BORDER_RED; /* 错误的方法 */
	box.us_view &= ~STYLE_MASK; /* 把样式位清0 */
	box.us_view |= B_DOTTED; /* 把样式设置为点 */
	printf("\nModified box settings:\n");
	show_settings(&box.st_view);
	printf("\nBox settings using unsigned int view:\n");
	show_settings1(box.us_view);
	printf("bits are %s\n",
		itobs(box.us_view, bin_str));

	system("pause");
	return 0;
}

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

void show_settings1(unsigned short us)
{
	printf("Box is %s.\n",
		(us & OPAQUE) == OPAQUE ? "opaque" : "transparent");
	printf("The fill color is %s.\n",
		colors[(us >> 1) & 07]);
	printf("Border %s.\n",
		(us & BORDER) == BORDER ? "shown" : "not shown");
	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 type.\n");
	}
	printf("The border color is %s.\n",
		colors[(us >> 9) & 07]);
}

char * itobs(int n, char * ps)
{
	int i;
	const static int size = CHAR_BIT * sizeof(int);
	for (i = size - 1; i >= 0; i--, n >>= 1)
		//01代表八进制1
		ps[i] = (01 & n) + '0';//1 + '0' 表示 '1'
	ps[size] = '\0';
	return ps;
}

运行测试