An interesting code about "struct" in "union"

Code:

union{
	struct st{
		char	c;
		char d;	
		short s;
	}token;
	int i;
}u;
int main(){
	u.i=0xff00dd01;
	char c = u.token.c;
	cout<<sizeof(u)<<endl;
}

My questions are:
1. why sizeof(u) is 4? I think it shall be 8 right?
2. What is c's value after execution?

thanks

1. why sizeof(u) is 4? I think it shall be 8 right?

Why should it be? An int is 4, and char is 1 (*2), short is 2, so the struct also adds up to 4.

2. What is c's value after execution?

0x1, assuming your machine is little-endian (therefore the least significant byte of i is stored first, overlapping with c)

2) c's value is green. Or marmelade. It depends on your system.

A union makes all members share the same memory, only with different representations. I've used this for binary readers as an example (to read structured data):

Code:

class CPointer
{
  public:
    union
    {
      void* Void;
      char* Char;
      short* Short;
      int* Int;
      float* Float;
    }
};

CPointer Pointer;

Pointer.Char = PointToDataSomwhere();

int IntVal1 = *Pointer.Int++;
int IntVal2 = *Pointer.Int++;
float FloatVal1 = *Pointer.Float++;
int IntVal3 = *Pointer.Int++;
float FloatVal2 = *Pointer.Float++;
float FloatVal3 = *Pointer.Float++;
short ShortVal1 = *Pointer.Short++;
int IntVal4 = *Pointer.Int++;

(forgive errors, I'm a C# user nowadays)