Yeah, DJBMASTER is right here: use the two code lines posted by him.

"HMmm...but if i remove the *, will the original p be altered ?"
Yes. In lite-C you can't pass structs by value, so p still points to your original struct.

"VecPlane orgP;
planesSetSize(orgP, 10);"
lite-C is supposed to differentiate between objects and pointers automatically (unless you set PRAGMA_POINTER). However, to be on the safe side you should use the address operator here: planesSetSize(&orgP, 10)