求助！c primer plus 中程序15.4

[weixin_40859919]

/* dualview.c -- bit fields and bitwise operators */
#include <stdio.h>
/* BIT-FIELD CONSTANTS */
/* opaque and show */
#define YES 1
#define NO 0
/* line styles */
#define SOLID 0
#define DOTTED 1
#define DASHED 2
/* primary colors */
#define BLUE 4
#define GREEN 2
#define RED 1
/* mixed colors */
#define BLACK 0
#define YELLOW (RED | GREEN)
#define MAGENTA (RED | BLUE)
#define CYAN (GREEN | BLUE)
#define WHITE (RED | GREEN | BLUE)

/* BITWISE CONSTANTS */
#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"};
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;
};

union Views /* look at data as struct or as unsigned short */
{
struct box_props st_view;
unsigned int ui_view;
};

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

int main(void)
{
/* create Views object, initialize struct box view */
union Views box = {{YES, YELLOW , YES, 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.ui_view);

printf("bits are %s\n",
itobs(box.ui_view,bin_str));
box.ui_view &= ~FILL_MASK; /* clear fill bits */
box.ui_view |= (FILL_BLUE | FILL_GREEN); /* reset fill */
box.ui_view ^= OPAQUE; /* toggle opacity */
box.ui_view |= BORDER_RED; /* wrong approach */
box.ui_view &= ~STYLE_MASK; /* clear style bits */
box.ui_view |= B_DOTTED; /* set style to dotted*/
printf("\nModified box settings:\n");
show_settings(&box.st_view);
printf("\nBox settings using unsigned int view:\n");
show_settings1(box.ui_view);
printf("bits are %s\n",
itobs(box.ui_view,bin_str));

return 0;
}

void show_settings(const struct box_props * pb)
{
printf("Box is %s.\n",
pb->opaque == YES? "opaque": "transparent");
printf("The fill color is %s.\n", colors[pb->fill_color]);
printf("Border %s.\n",
pb->show_border == YES? "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]);

}

/* convert int to binary string */
char * itobs(unsigned int n, char * ps)
{
int i;
static int size = 8 * sizeof(unsigned int);

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

return ps;
}

程序原理理解了。不理解为什么 struct box_props 中两个一位的变量opaque 和 show_border设置成unsigned 就行，设成bool型变量就不对了。

按照我贴的程序结果如图，与书本完美契合

按照第六版书上程序，即用bool型，结果如图，不行

[sghcpt]

因为你把unsigned int改为bool，struct box_props结构体的大小已经改变了，在我测试的编译器中是变大了，由原来的4个字节变为16个字节了，这可能涉及到位域的概论了，所以你代码中union Views组合类型的占用的内存字节数就变大了，而不是原来的4个字节了。即之前每个字段位对应的值可能就改变了。所以在结构体中使用位域时，最好每个字段的类型都一致，这样就简单点。

[自信男孩]

bool是int类型。而不是unsigned int

[真相重于对错]

c 没有bool c++才有

[weixin_40859919]

引用 1 楼 cfjtaishan 的回复:

bool是int类型。而不是unsigned int

谢谢！

[weixin_40859919]

引用 3 楼 hdt 的回复:

c 没有bool
c++才有

有的。c11有。