union中内嵌struct

#include<iostream>
using namespace std;
//用来解析
// bit-field used to unpack the st_mode in field in a _stat structure
struct modes
{
    unsigned others : 3;    // permissions for everyone else
    unsigned group  : 3;    // group permissions
    unsigned user   : 3;    // file owner permissions
    unsigned type   : 7;    // other file data - directory or regular file?
};

//在16bit和mode 位间映射
union map    // used to map between a 16-bit int and a mode bit field.
{
    unsigned short statmode;    // data input as 16-bit int  已16-bit输入
    modes convert;            // data output as modes bit field. 位域输出
};

int main()
{
    map    mapper;
    //存储16-bit整数到mapper的statmode域
//store a 16-bit integer into the mapper‘s statmode field
    mapper.statmode =0x88;

//read the unpacked information out of the mapper‘s convert field, which further divides the data into bit-fields
//从mapper转换域读解析信息，然后分数据到位域
    cout << mapper.convert.user << endl;
    cout << mapper.convert.group << endl;
    cout << mapper.convert.others << endl;

}