When I want to refactoring some C code, 1522 will using the C++ technology "reference", but there is no reference in C, so those code can't be compiled,
for now the best advice is to either select the extracted method and use find / replace on the selected code to turn "foo." into "foo->" and then fix any errors, or to avoid extract method in C for now. most (or even all) of the other refactoring operations should be fine in C.