does order of members of objects of a class have any impact on performance?

Question

May order of members in binary architecture of objects of a class somehow have an impact on performance of applications which use that class? and I\'m wondering about how to dec

Answer 1

In addition to the runtime performance, described in the cache-line related answers, I think one should also consider memory performance, i.e. the size of the class object.

Due to the padding, the size of the class object is dependent on the order of member variable declaration.

The following declaration would probably take 12 bytes

class foo {
    char c1;
    int  i;
    char c2;
}

However, upon simple re-ordering of the order of member declaration, the following would probably take 8 bytes

class bar {
    int  i;
    char c1;
    char c2;
}

In machines aligned with 4-byte words:

sizeof( foo ) = 12

but

sizeof( bar ) = 8