TN.164.MPW C Functions - Here’s the low-down on when C functions need not be declared in include files. “The include files are all screwed up!” This is a common misconception people have when they look through the MPW C include files. People report that the declaration of a ROM or system call foo() has been mistakenly left out of this or that include file. Here’s the low-down on when functions do not have to be declared in an include file.