C++ vector, return vs. parameter [duplicate]

Answer 1

Adding a fourth variant into the mix:

void FillVector_4(vector& v) {
   static const int tab[SZ] = {1,2,3, ... };
   v.assign(tab,tab+SZ);
}

If you're thinking about performance version 2 and version 3 may make the compiler create a vector copy for the return value. That is, if the compiler isn't able to do NRVO (named return value optimization). Also, consecutive push_backs without a reserve probably leads to a couple of reallocations since the vector needs to grow. Whether this matters at all depends on your problem you're trying to solve.

You'll be pleased to know that C++0x will make returning a locally created vector very efficient. I also recommend reading David Abrahams article series about efficient value types including passing/returning.