struct定义中在成员后面加冒号“:typedef unsigned char u_char;struct frame_control {u_char fc_subtype :4;u_char fc_type :2;u_char fc_protocol_version :2;u_char fc_order :1;u_char fc_wep :1;u_char fc_more_data :1;u_char fc_pwr_mgt :1;u_cha
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![struct定义中在成员后面加冒号“:typedef unsigned char u_char;struct frame_control {u_char fc_subtype :4;u_char fc_type :2;u_char fc_protocol_version :2;u_char fc_order :1;u_char fc_wep :1;u_char fc_more_data :1;u_char fc_pwr_mgt :1;u_cha](/uploads/image/z/5324468-68-8.jpg?t=struct%E5%AE%9A%E4%B9%89%E4%B8%AD%E5%9C%A8%E6%88%90%E5%91%98%E5%90%8E%E9%9D%A2%E5%8A%A0%E5%86%92%E5%8F%B7%E2%80%9C%EF%BC%9Atypedef+unsigned+char+u_char%3Bstruct+frame_control+%7Bu_char+fc_subtype+%3A4%3Bu_char+fc_type+%3A2%3Bu_char+fc_protocol_version+%3A2%3Bu_char+fc_order+%3A1%3Bu_char+fc_wep+%3A1%3Bu_char+fc_more_data+%3A1%3Bu_char+fc_pwr_mgt+%3A1%3Bu_cha)
struct定义中在成员后面加冒号“:typedef unsigned char u_char;struct frame_control {u_char fc_subtype :4;u_char fc_type :2;u_char fc_protocol_version :2;u_char fc_order :1;u_char fc_wep :1;u_char fc_more_data :1;u_char fc_pwr_mgt :1;u_cha
struct定义中在成员后面加冒号“:
typedef unsigned char u_char;
struct frame_control {
u_char fc_subtype :4;
u_char fc_type :2;
u_char fc_protocol_version :2;
u_char fc_order :1;
u_char fc_wep :1;
u_char fc_more_data :1;
u_char fc_pwr_mgt :1;
u_char fc_retry :1;
u_char fc_more_frag :1;
u_char fc_from_ds :1;
u_char fc_to_ds :1;
};
里面成员定义中加:
struct定义中在成员后面加冒号“:typedef unsigned char u_char;struct frame_control {u_char fc_subtype :4;u_char fc_type :2;u_char fc_protocol_version :2;u_char fc_order :1;u_char fc_wep :1;u_char fc_more_data :1;u_char fc_pwr_mgt :1;u_cha
这是位域操作的表示方法,也就是说后面加上“:1”的意思是这个成员的大小占所定义类型的1 bit,“:2”占2 bit,依次类推.当然大小不能超过所定义类型包含的总bit数.
一个bytes(字节)是8 bit(bit).例如你的结构中定义的类型是u_char,一个字节,共8bit,最大就不能超过8.
32位机下,
short是2字节,共16bit,最大就不能超过16.
int是4字节,共32bit,最大就不能超过32.
依次类推.
这样定义比较省空间.例如你上面的结构,定义的变量类型是u_char,是一字节类型,即8bit.
fc_subtype占了4bit,fc_type占2bit,fc_protocol_version占2bit,共8bit,正好是一个字节.
其他八个成员,各占1bit,共8bit,正好也是一个字节.
因此你的结构的大小如果用sizeof(struct frame_control)计算,就是2bytes.