We have a huge C, and C++ code base. There is a plan to add a new feature into the existing system, but, this should happen only after 3 to 4 months.

So, we are looking for best possible options.

1. Branching off is one option, but, this involves porting the bug fixes to the feature branch from the trunk.
2. Staying on the trunk itself, have ifdef to differentiate the new feature compilation
3. Split the source/header files that involve the new feature, edit the makefiles to pick the right file.

I understand this question is pretty vague, and only people working on it can well decide the way forward. But, I'm looking for generalized opinions on a case like this.