结构体 填充字段 知道的高手请进

[新屿]

C专家编程中，
结构体填充字段，
struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
short pid_id;
struct pid_tag *link;
} 看不明白。
填充字段是否占内存空间？如果占，占多少？是否是后面填充的数值？？这里很模糊，望理解的高手解释的清楚点。谢谢

[ouyh12345]

inactive占一位

[新屿]

[Quote=引用 1 楼 ouyh12345 的回复:]

inactive占一位
[/Quote]
能解释清楚点不，第一个int 变量如果占以为，那第二个呢，其中关于到字段填充，内存是怎么分配的？？？

[nice_cxf]

unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
由于一共8<32,因此一共占用sizeof(int)

[新屿]

[Quote=引用 3 楼 nice_cxf 的回复:]

unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
由于一共8<32,因此一共占用sizeof(int)
[/Quote]
struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
short pid_id;
struct pid_tag *link;
}
我sizeof上面的，结果是12
如果不填充那24个bit，
即：struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
short pid_id;
struct pid_tag *link;
}
这样sizeof的结果是8
如果下面的形式
struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
// short pid_id;
struct pid_tag *link;
}
sizeof的结果还是8
如果struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
// short pid_id;
// struct pid_tag *link;
}
sizeof结果是4
方便对照这个解释下吗？谢谢

[振翅高飞]

LZ看看这两篇吧，看完就懂了
http://apps.hi.baidu.com/share/detail/15820795
http://www.programfan.com/blog/article.asp?id=30210

[gqjjqg]

[Quote=引用 4 楼 zywx870823 的回复:]

引用 3 楼 nice_cxf 的回复:

unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
由于一共8<32,因此一共占用sizeof(int)

struct pid_tag{
unsigned int inactive :1;
……
[/Quote]

首先明确你是多少字节对齐的。

我这边是4字节对齐：
struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
short pid_id;
struct pid_tag *link;
} 这个是12
struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
short pid_id;
struct pid_tag *link;
} 这个还是12
struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
// short pid_id;
struct pid_tag *link;
} 这个是 8

struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
// short pid_id;
// struct pid_tag *link;
} 这个是4

[peng_weida]

字节对齐

[nice_cxf]

如果不填充那24个bit，
即：struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
// unsigned int :0;
short pid_id;
struct pid_tag *link;
}
引用 3 楼 nice_cxf 的回复:

unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
由于一共8<32,因此一共占用sizeof(int)

struct pid_tag{
unsigned int inactive :1;
unsigned int :1;
unsigned int refcount : 6;
unsigned int :0;
short pid_id;
struct pid_tag *link;
}
我sizeof上面的，结果是8
你确定是8么？什么编译器？我在vs2008下测试是12，unsigned int :0;加不加应该没关系啊