sizeof

 union V {

struct X {

unsigned char s1:2;

unsigned char i:3;

} x;

 

unsigned char c;

  } v;

int n = sizeof(v);   //1

int l = sizeof(v.x);  //1

 

 

 

 union V {

struct X {

unsigned char s1:2;

unsigned char i;

} x;

 

unsigned char c;

  } v;

int n = sizeof(v);   //2

int l = sizeof(v.x);  //2