mikejsavage.co.uk / blog

25 Jun 2017 / C++ tricks: NO_INIT

This one is very simple and I'm surprised I've not written it down already.

Default initialisation is widely considered to be good, but if you're being a performance nut you might want to opt-out. In D you can do int x = void;. Rust apparently has mem::uninitialized(). You can do the same thing in C++ thusly:

enum class NoInit { DONT };
#define NO_INIT NoInit::DONT // if you want
struct v3 {
        float x, y, z;
        v3() { x = y = z = 0; }
        v3( NoInit ) { }

v3 a;
v3 b( NO_INIT );
// a = (0, 0, 0) b = (garbage)

On a similar note, in my code I prefer to design my structs so that all zeroes is the default state, and then my memory managers all memset( 0 ) when you allocate something. I find it easier than getting proper construction right, and I've heard that echoed by a few other people so I guess it's not a totally bunk idea.