On Friday, May 31, 2013 23:19:57 Shriramana Sharma wrote: > > However, :) if you are going to make a copy of the argument anyway, always > > take a struct by-value. That works with both lvalue and rvalue arguments > > and in the case of rvalues, you will get the automatic move semantics. > > > > My choice is by-value for structs unless there is any reason not to. > > So where is the cut-off point? I mean, by-value means a copy is done > every time the function is called right?
The compiler will move an object rather than copy it when it can. So, for instance, if you pass the function a temporary, it'll move that temporary rather than copying it. However, if it's called with an lvalue, odds are that it's going to have to make a copy (though it might be moved if it were the last time in the caller that the variable was referenced). > So how heavy (in terms of > sizeof) would a struct have to be to make passing by ref more > efficient than passing by value? That would depend on the compiler. You'd have to do tests to see. Certainly, for anything that's small enough to fit in a register, it's likely to be faster to pass by value. But how much beyond that the struct has to grow before it's large enough that passing by reference would be cheaper, I don't know. A lot that the compiler does could affect that. The only way to know for sure is to test it. - Jonathan M Davis
