Re: replicating default constructor's "non-initializing state"

Tamas Demjen <>
Tue, 08 Apr 2008 18:02:57 -0700
Jason Doucette wrote:

No, it's not my choice. I do *not want* to make a default constructor
myself. I want to keep the original default constructor that does no
initialization. But, C++ is forcing me to make my own.

You can write a do-nothing constructor, but even that will be heavier
than not having a constructor at all:

struct C
    C() { }

This is the most lightweight solution you can do in C++ if you already
have another constructor. Of course the compiler might add some implicit
function calls to it. However, if your structure only contains POD
types, they will remain uninitialized. There's a good chance the
compiler can inline this for you, and remove the empty body.

Another solution to consider: simply don't write your own constructor at
all. Create a static function, or a non-member function to initialize
your data. Example:

struct Color
    int r, g, b;
    static Color Create(int ar, int ag, int ab)
       Color c;
       c.r = ar;
       c.g = ag;
       c.b = ab;
       return c;

This has to perform two assignment operations for each member, though.
If performance is really so important for you, you might want to use a
less convenient method:

inline void InitColor(Color& c, int ar, int ag, int ab)
    c.r = ar;
    c.g = ag;
    c.b = ab;

The compiler will likely inline this for you in release builds. And
there's always a possibility of using a macro (ouch!).

Otherwise my tip would be to avoid early optimizations, and optimize
only after doing some benchmarking. Did you know that calling malloc
just once can be a thousand times slower than initializing those
integers with 0? There is a possibility that you're trying to optimize
something that's not likely to be anywhere near the bottleneck.


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