Initialize LUT in C with macros?

Question

I need a look-up-table in my program describing the size of different types. Right now I got it like:

typedef struct{
     APP_InterfaceType_t Type;  //This is just an enum
     uint8_t Size;
}APP_InterfacesLUT_t;

APP_InterfacesLUT_t MyLUT[] = {...}

Now problem is, I want to insert the content of the LUT from different .h files (I have my reasons) and it has to be done in the pre-processor.

I got the different types in separate .h files, and when I include one of these .h files in my build, the type (described in the .h file) and size should magically appear in the LUT.

So I am wondering if this is possible by calling some kind of Macro inside the .h files?

for example:

REGISTERTYPE(type, size); 

EDIT: The module where the LUT is defined doesn't know anything about the types. The idea is that when I want to add a new type to the program, I only have to include a header-file and not edit anything in the rest of the program :)

Answer 1

Yes, that's possible, but it will probably require you to use some multiple-inclusion and/or ifdef trickery.

See also X macros , but it becomes more complicated when you need to generalize it to work across multiple headers.

Answer 2

You could do conditional compilation if your LUT module knows about other modules. There are many approaches to this (like X-macros as unwind pointed out), but here's something traditional:

APP_InterfacesLUT_t MyLUT[] = {
#ifdef MODULE_A
    { TYPE_1, 12 },
    { TYPE_2, 45 },
#endif
#ifdef MODULE_B
    { TYPE_2, 22 },
    { TYPE_3, 77 },
#endif
};

If your LUT module doesn't know about other modules, then there's no way around it and you must do this at runtime.

Edit:

X-macro solution.

LUT.c:

APP_InterfacesLUT_t MyLUT[] = {
    #define X(a, b, c)   { a, b },
    #include "interfaces.x"
    #undef X
};

interfaces.x:

// Molude A
X( TYPE_1, 12, something else )
X( TYPE_2, 45, something else )
// Molude B
X( TYPE_2, 22, something else )
X( TYPE_3, 77, something else )