Data structure padding

Question

What is data structure padding in c++ and how do i check the number of bytes padded bytes?

class a { public: int x; int y; int z; };

Answer 1

Processors require that certain types of data have particular alignments. For example, a processor might require that an int be on a 4-byte boundary. So, for example, an int could start at memory location 0x4000 but it could not start at 0x4001. So if you defined a class:

class a
{
public:
    char c;
    int i;
};

the compiler would have to insert padding between c and i so that i could start on a 4-byte boundary.