Should Local Variable Initialisation Be Mandatory?

Question

The maintenance problems that uninitialised locals cause (particularly pointers) will be obvious to anyone who has done a bit of c/c++ maintenance or enhancement, but I still se

Answer 1

As you've showed with respect to performacne it does not make a difference. The compiler will (in optimized builds) detect if a local variable is written without beeing read from and remove the code unless it has other side-effects.

That said: If you initialize stuff with simple statements just to be sure it's initialized it's fine to do so.. I personally don't do it, for a single reason:

It tricks the guys who may later maintain your code into thinking that the initialization is required. That little foo = 0; will increase the code-complexity. Other than that it's just a matter of taste.

If you unnessesary initialize variables via complex statements it may have a side-effect.

For example:

  float x = sqrt(0);

May be optimized by your compiler if you are lucky and work with a clever compiler. With a not so clever compiler it may as well result in a costly and unnessesary function-call because sqrt can - as a side-effect - set the errno variable.

If you call functions that you have defined yourself my best bet is, that the compiler always assumes that they may have side-effects and don't optimize them out. That may be different if the function happen to be in the same translation unit or you have whole program optimization turned on.