The size of a class can be changed simply by playing with the order of its members' declaration:
On my machine, sizeof (A) equals 12. This result might seem surprising because the total size of A's members is only 6 bytes: 1+4+1 bytes. Where did the remaining 6 bytes come from? The compiler inserted 3 padding bytes after each bool member to make it align on a four-byte boundary. You can reduce A's size by reorganizing its data members as follows:
This time, the compiler inserted only 2 padding bytes after the member c. Because b occupies four bytes, it naturally aligns on a word boundary without necessitating additional padding bytes.
Code: CPP
struct A
{
bool a;
int b;
bool c;
}; /*sizeof (A) == 12*/
On my machine, sizeof (A) equals 12. This result might seem surprising because the total size of A's members is only 6 bytes: 1+4+1 bytes. Where did the remaining 6 bytes come from? The compiler inserted 3 padding bytes after each bool member to make it align on a four-byte boundary. You can reduce A's size by reorganizing its data members as follows:
Code: CPP
struct B
{
bool a;
bool c;
int b;
}; // sizeof (B) == 8
This time, the compiler inserted only 2 padding bytes after the member c. Because b occupies four bytes, it naturally aligns on a word boundary without necessitating additional padding bytes.
