c++ Class default property - c++

Question

Is there a way in c++ to set a property in a union/class/struct as a default one? I use Visual Studio.
The idea is to be able to access them without having to reference it. Something like:
typedef uint64_t tBitboard;
union Bitboard {
tBitboard b; //modifier somewhere in this line to set as default
uint8_t by[8];
};
Bitboard Board;
And then I want to access:
Board=100;
that puts 100 in Board.b
Or
Board.by[3]=32;
so to put 32 in the byte 3 of the array. I think this is not possible, but may be someone knows a way.
Thanks!
Nice solutions!
I’m trying to use this one:
union Bitboard {
tBitboard b;
std::uint8_t by[8];
Bitboard(tBitboard value = 0) { b = value; }
Bitboard& operator = (tBitboard value) { b = value; return *this; }
};
But with in this line there is an error:
if (someBitboard)
Error 166 error C2451: conditional expression is not valid
Thanks

Answer 1

You might add constructors and operators to the union:
#include <iostream>
#include <iomanip>
typedef std::uint64_t tBitboard;
union Bitboard {
tBitboard b;
std::uint8_t by[8];
Bitboard(tBitboard value = 0) { b = value; }
Bitboard& operator = (tBitboard value) { b = value; return *this; }
std::uint8_t& operator [] (unsigned i) { return by[i]; }
};
int main()
{
// Construct
Bitboard Board = 1;
// Assignment
Board = tBitboard(-1);
// Element Access
Board[0] = 0;
// Display
unsigned i = 8;
std::cout.fill('0');
while(i--)
std::cout << std::hex << std::setw(2) << (unsigned)Board[i];
std::cout << '\n';
return 0;
}
This is covered in 9.5 Unions:
A union can have member functions (including constructors and destructors), but not virtual (10.3) functions.
Note: Please be aware of platform dependencies regarding the memory layout (endianess) of values.

Answer 2

You can overload = operator:
class C
{
public:
void operator = (int i)
{
printf("= operator called with value %d\n", i);
}
};
int main(int argc, char * argv[])
{
C c;
c = 20;
getchar();
}
Be careful though when overloading operators, which have some default behavior. It may be easier for you to use your class, but harder to others to catch up on your conventions. Using bit shift operators - as Bgie suggested - would be a better idea here.
If you publish an array, you can freely access its elements:
class C
{
public:
int b[5];
};
int main(int argc, char * argv[])
{
C c;
c.b[2] = 32;
}