Function Prototypes

Function prototypes are more important in the 64-bit programming environment than the 32-bit programming environment, because the default return value of an undeclared function is int.

If a function prototype is missing for a function returning a pointer, the compiler will convert the returned value to an int by setting the high-order word to 0, corrupting the value. In addition, function prototypes allow the compiler to do more type checking, regardless of the compilation mode.

When compiled in 64-bit mode, system header files define full function prototypes for all kernel services provided by the 64-bit kernel. By defining the __FULL_PROTO macro, function prototypes are provided in 32-bit mode as well. It is recommended that function prototypes be provided by including the system header files, instead of providing a prototype in a source file.