Question

Got a question for you all. Many of you will answer ‘it makes no difference’ but I’m somewhat adamant there is a difference due to the wording of the question:

‘Which class uses the least amount of memory?’

They’re asking for a singular answer – there must be one! I’ve had a chat with a previous Microsoft intern and he’s adamant there is no answer.

Maybe some would care to offer their thoughts?

Which class uses the least amount of memory?

class A 
{
    float duration;
    char code;
    int count;
    bool enabled;
};

class B 
{
    float duration;
    int count;
    char code;
    bool enabled;
};

class C
{
    char code;
    int count;
    bool enabled;
    float duration;
};

class D
{
    bool enabled;
    float duration;
    char code;
    int count;
};

Answer 1

On MSVC2010 I get

A = 16 bytes
B = 12 bytes
C = 16 bytes
D = 16 bytes

this is probably due to alignment of the different types. Since char and bool are both small they share a DWORD.

However this is compiler and platform independent. There is nothing stopping a compiler implementer from making them all the same size or making a char 64 bytes or whatever. The requirements of the standard are quite lax about this kind of thing.