Barring any agreement otherwise, the code's copyright belongs to the individual developer who wrote it, though in the case of software projects this may get a little weird when multiple developers write and overwrite each other's code.

The following is speculation, because I've read up on the finer points of copyright laws as applied to purely digital property, but by sharing the code the developer has obviously gave the person he's sharing the code with implicit permission to work and use that copy of that code, although, again barring any prior agreement otherwise, he should also be able to rescind that permission as he chooses.