Preprocessor Macro Function that allows for GUI Library Expansion - c-preprocessor

I am attempting to create a Preprocessor Macro Function that registers callback functions for my own GUI Library I am making. The library is designed to be easily expanded by 3rd parties by using the Macro function mentioned above.
My Problem: My macro function includes other preprocessor directives which I think are not allowed. I want to code my REGISTER_CUSTOM_CALLBACK_FUNCTION in a way that allows the user to create their own widgets and register their own callback function with the main GUI library. Any ideas how I can still achieve what I am trying to do?
#define FORWARD_DECLARE_CALLBACK_FUNCTION(callbackFunctName) Integer callbackFunctName(Draw_Box& window, Integer windowIndex, Integer id, Text cmd, Text msg);
#define REGISTER_CUSTOM_CALLBACK_FUNCTION(callbackFunctName) \
#ifndef CUSTOM_CALLBACK_1 \
#define CUSTOM_CALLBACK_1 \
FORWARD_DECLARE_CALLBACK_FUNCTION(callbackFunctName) \
#elif !defined CUSTOM_CALLBACK_2 \
#define CUSTOM_CALLBACK_2 \
FORWARD_DECLARE_CALLBACK_FUNCTION(callbackFunctName) \
#endif
// Intended Usage: In a customers code they will be able to create their own
// Widgets with their own Window Callback functions like this...
REGISTER_CUSTOM_CALLBACK_FUNCTION(progressBarCallback)
... some other code
REGISTER_CUSTOM_CALLBACK_FUNCTION(hyperlinkCallback)
Heres the main window callback that is called each clock step:
Integer main_callback(Draw_Box& window, Integer windowIndex, Integer id, Text cmd, Text msg)
{
#ifdef CUSTOM_CALLBACK_1
CUSTOM_CALLBACK_1(window, windowIndex, id, cmd, msg);
#endif
#ifdef CUSTOM_CALLBACK_2
CUSTOM_CALLBACK_2(window, windowIndex, id, cmd, msg);
#endif
}
Any ideas how I could code my REGISTER_CUSTOM_CALLBACK_FUNCTION to allow the user to create their own widgets and register their own callback function with the main GUI library?

Related

Default arguments to C macros

Suppose I have function bshow() with signature
void bshow(int arg0, int arg1, int arg2);
but for arbitrary reasons I want to implement it as a macro.
Furthermore, I want the function have default arguments
int arg0=0x10;
int arg1=0x11;
int arg2=0x12;
I've already done this for the case that bshow() is a function, using the standard tricks.
But how can I do it as a macro?
Eg. suppose I have a macro nargs() that uses the C Preprocessor to count the number of arguments. Eg.
nargs() // get replaced by 0 by the preprocessor
nargs(a) // get replaced by 1 by the preprocessor
nargs(a,b) // get replaced by 2 by the preprocessor
I'd like to do something like (which doesn't work):
#define arg0_get(a0,...) a0
#define arg1_get(a0,a1,...) a1
#define arg2_get(a0,a1,a2,...) a2
#define bshow(...) do{ \
int arg0=0x10; if(0<nargs(__VA_ARGS__)) arg0 = arg0_get(__VA_ARGS__); \
int arg1=0x11; if(1<nargs(__VA_ARGS__)) arg1 = arg1_get(__VA_ARGS__); \
int arg2=0x12; if(2<nargs(__VA_ARGS__)) arg2 = arg2_get(__VA_ARGS__); \
/* do stuff here */ \
}while(0)
Actually I've already implemented the bshow() function as a macro, as follows (here it has the actual number of arguments):
#define __bshow(bdim,data, nbits,ncols,base)({ \
bdim,data, nbits,ncols,base; \
putchar(0x0a); \
printf("nbits %d\n",nbits); \
printf("ncols %d\n",ncols); \
printf("base %d\n",base); \
})
#define _bshow(bdim,data, nbits,ncols,base, ...) __bshow(bdim,data, nbits,ncols,base)
#define bshow(...) \
if( 2==nargs(__VA_ARGS__)) _bshow(__VA_ARGS__, 32,24,16,0,__VA_ARGS__); \
else if(3==nargs(__VA_ARGS__)) _bshow(__VA_ARGS__, 24,16,0,__VA_ARGS__); \
else if(4==nargs(__VA_ARGS__)) _bshow(__VA_ARGS__, 16,0,__VA_ARGS__); \
else if(5==nargs(__VA_ARGS__)) _bshow(__VA_ARGS__, 0,__VA_ARGS__); \
// test
bshow(0,1);
bshow(0,1, 10);
bshow(0,1, 10,11);
bshow(0,1, 10,11,12);
EDIT:
The proposed solution doesn't have the intended effect because it seems to "instantiate" all instances of the macro, which in general has unintended consequences.
But I wonder if there's a more elegant way to do it.
It'd also be nice to abstract away the entire construction inside its own macro, so that one can apply it to other functions easily, as opposed to having to write the boilerplate manually for each function/macro.
Also this wasn't too helpful.

I found a nice answer.
What you do is you call the vfn() macro, which is (I think) a higher-order macro that returns a macro that returns the token concatenated with the number of args (in hex base, no 0-padding) and then evaluates it at the args. Or something.
Eg. supposed you want to overload a macro called bshow(). You #define the macro bshow() as #define bshow() vfn(bshow,__VA_ARGS__), and you define 1 instance of bshow for each argument count (eg. #define bshow0(...), for 0 arguments, #define bshow1(...) for 1 argument, #define bshow2(...) for 2 arguments, etc.). So now, eg., bshow(0,1) returns bshow2() (because you called it with 2 arguments) evaluated at (0,1), which is _bshow(0,1, 16,32,16), and then _bshow(0,1, 16,32,16) gets evaluated too. You can check the final preprocessor output by running gcc with the -E option, but the intermediate steps are hard to understand (for me).
You also need to decide on the mandatory args and the optional args.
That's almost all I (sort of) understand about what's going on, although I did upload a YT tutorial a while ago on how the argument-counting works.
// ----------------------------------------------------------------
// library
#define __nargs100__(a00,a01,a02,a03,a04,a05,a06,a07,a08,a09,a0a,a0b,a0c,a0d,a0e,a0f,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19,a1a,a1b,a1c,a1d,a1e,a1f,a20,a21,a22,a23,a24,a25,a26,a27,a28,a29,a2a,a2b,a2c,a2d,a2e,a2f,a30,a31,a32,a33,a34,a35,a36,a37,a38,a39,a3a,a3b,a3c,a3d,a3e,a3f,a40,a41,a42,a43,a44,a45,a46,a47,a48,a49,a4a,a4b,a4c,a4d,a4e,a4f,a50,a51,a52,a53,a54,a55,a56,a57,a58,a59,a5a,a5b,a5c,a5d,a5e,a5f,a60,a61,a62,a63,a64,a65,a66,a67,a68,a69,a6a,a6b,a6c,a6d,a6e,a6f,a70,a71,a72,a73,a74,a75,a76,a77,a78,a79,a7a,a7b,a7c,a7d,a7e,a7f,a80,a81,a82,a83,a84,a85,a86,a87,a88,a89,a8a,a8b,a8c,a8d,a8e,a8f,a90,a91,a92,a93,a94,a95,a96,a97,a98,a99,a9a,a9b,a9c,a9d,a9e,a9f,aa0,aa1,aa2,aa3,aa4,aa5,aa6,aa7,aa8,aa9,aaa,aab,aac,aad,aae,aaf,ab0,ab1,ab2,ab3,ab4,ab5,ab6,ab7,ab8,ab9,aba,abb,abc,abd,abe,abf,ac0,ac1,ac2,ac3,ac4,ac5,ac6,ac7,ac8,ac9,aca,acb,acc,acd,ace,acf,ad0,ad1,ad2,ad3,ad4,ad5,ad6,ad7,ad8,ad9,ada,adb,adc,add,ade,adf,ae0,ae1,ae2,ae3,ae4,ae5,ae6,ae7,ae8,ae9,aea,aeb,aec,aed,aee,aef,af0,af1,af2,af3,af4,af5,af6,af7,af8,af9,afa,afb,afc,afd,afe,aff,a100,...) a100
#define __nargs__(...) __nargs100__(,##__VA_ARGS__, ff,fe,fd,fc,fb,fa,f9,f8,f7,f6,f5,f4,f3,f2,f1,f0,ef,ee,ed,ec,eb,ea,e9,e8,e7,e6,e5,e4,e3,e2,e1,e0,df,de,dd,dc,db,da,d9,d8,d7,d6,d5,d4,d3,d2,d1,d0,cf,ce,cd,cc,cb,ca,c9,c8,c7,c6,c5,c4,c3,c2,c1,c0,bf,be,bd,bc,bb,ba,b9,b8,b7,b6,b5,b4,b3,b2,b1,b0,af,ae,ad,ac,ab,aa,a9,a8,a7,a6,a5,a4,a3,a2,a1,a0,9f,9e,9d,9c,9b,9a,99,98,97,96,95,94,93,92,91,90,8f,8e,8d,8c,8b,8a,89,88,87,86,85,84,83,82,81,80,7f,7e,7d,7c,7b,7a,79,78,77,76,75,74,73,72,71,70,6f,6e,6d,6c,6b,6a,69,68,67,66,65,64,63,62,61,60,5f,5e,5d,5c,5b,5a,59,58,57,56,55,54,53,52,51,50,4f,4e,4d,4c,4b,4a,49,48,47,46,45,44,43,42,41,40,3f,3e,3d,3c,3b,3a,39,38,37,36,35,34,33,32,31,30,2f,2e,2d,2c,2b,2a,29,28,27,26,25,24,23,22,21,20,1f,1e,1d,1c,1b,1a,19,18,17,16,15,14,13,12,11,10,f,e,d,c,b,a,9,8,7,6,5,4,3,2,1,0)
#define __vfn(name, n) name##n
#define _vfn( name, n) __vfn(name, n)
#define vfn( fn, ...) _vfn(fn, __nargs__(__VA_ARGS__))(__VA_ARGS__)
// ----------------------------------------------------------------
// example
// backend: actual implementation, 2 mandatory args, 3 optional args
#define _bshow(bdim,data, ncols,nbits,base)({ \
/* do stuff here */ \
})
// "frontend", default arguments get implemented here. the suffix is the number of arguments, in hexadecimal base
#define bshow2(...) _bshow(__VA_ARGS__, 16,32,16)
#define bshow3(...) _bshow(__VA_ARGS__, 32,16)
#define bshow4(...) _bshow(__VA_ARGS__, 16)
#define bshow5(...) _bshow(__VA_ARGS__)
#define bshow(...) vfn(bshow,__VA_ARGS__)
// test
bshow(0x100,data0);
bshow(0x100,data0, 14);
bshow(0x100,data0, 12,16);
bshow(0x100,data0, 10, 8,2);

C header declaration for generics (macro)

I am unsure about where to write the declaration and the call of a macro that replaces the code with a function. I do not really know if I should write the macro to the .h or .c file.
Before reading some stuff on the best ways to create libraries, I was just putting all the code in a header file and including it on my main, i.e.
#ifndef LIB
#define LIB
#define def_func(type) \
type func(type x) \
{ \
// Do something
}
func(int)
#endif
Some other functions use these defined functions so I had to call the macro to the .h file.

Firstly, I think that a few small edits are needed in the code from the question:
#ifndef LIB
#define LIB
#define def_func(type) \
type func(type x) \
{ \
/* Do something */ \
}
def_func(int)
#endif
The question does not detail what objective is being achieved, but I would assume that the goal is to create something that behaves like a template in C++, where the code is defined in one place and instances are created for different types by using the macro def_func.
One thing to be aware of is if you are using def_func more than once in your project, then you are going to have linker errors due to the same global symbol being used in multiple places, even if def_func is used in separate files. This could be avoided by making the function static if def_func is used multiple times but never more than once in the same file. Although, this would restrict the function from being called from multiple files.
Global symbol redefinition could also be avoided by adding another argument to the #define as follows:
#define def_func(func, type) \
type func(type x) \
{ \
/* Do something */ \
}
This would allow the function identifier to be specified uniquely. For example:
def_func(func_int, int)
would expand to:
int func_int(int x)
{
/* Do something */
}
This way a unique identifier would be created for each instance.
The #define should be placed in the header file if you intend to use the macro from multiple C source files. The macro should be used within C source files only, since using this in the header file would instantiate an object with the same global symbol in each case the header file is included. Although, this would be allowable if the functions are defined as static.
Lastly, if you plan to call the function created from multiple locations, you will need a macro that can be used in a header file associated with the module defining the function to prototype the function. For example:
#define def_func_proto(func, type) \
type func(type x)
So to sum it up, your library .h file would contain:
#define def_func(func, type) \
type func(type x) \
{ \
/* Do something */ \
}
#define def_func_proto(func, type) \
type func(type x)
Then using the integer case as an example, the C source file may include:
def_func(func_int, int)
Which would expand to (note that the actual expansion will not have line breaks):
int func_int(int x)
{
/* Do something */
}
In this case, the header file may contain:
def_func_proto(func_int, int);
Which would expand to:
int func_int(int x);
Finally, I would note that am not certain that this is a good programming practice, in general. You will want to be very cautious in implementing this in your program.

Use specific entry of an X macro

I am using X macros to generate functions setting GPIOs to 0 or 1 (I generate around 60 functions to set around 30 GPIOs). Here is an example (I have just written this example, so the syntax may be wrong):
/* X(pin_name, pin_nb) */
#define CPLD_GPIOs \
X(Pin0, 0) \
X(Pin1, 1) \
X(Pin2, 2) \
X(Pin3, 3)
I generate the functions to access to these GPIOs:
#define X(pin_name, pin_nb) \
static void SetOn_GPIO##pin_name (void) { \
SetOn_GPIOpins(pin_nb);\
}
CPLD_GPIOs
#undef X
The same process exists for SetOff_GPIOXXX functions.
Is there a way I can access the function generated above by the compiler as SetOn_GPIOPin2 in an other part of the program without directly writing the function name? (In order to keep the code as global as possible)
At the end of preprocessing, we should only have SetOn_GPIOPin2(); (and not every X-macro entries) generated from X-Macro.
Before pre-processing:
void foo ()
{
/* some code */
/*
* Macro to generate the desired function.
* For e.g: SetOn_GPIOPin2();
*/
/* some code */
}
After pre-processing:
void foo ()
{
/* some code */
/* Function resulting of the pre-processing */
SetOn_GPIOPin2();
/* some code */
}

From comments on the question, your objective appears to be to protect against the case in which your X macro is modified to produce differently-named functions. If that's so, then I think you're making unnecessary work for yourself: whether those names are changed is under your (and any other project developers') control, and a name change such as you are concerned about will not go unnoticed very long. So don't change them.
But if you're determined to go this route then no, there is no way to make the preprocessor extract the function names generated by your macros from their larger replacement text. Instead, you would need to inject them, via the same macro, into both the X macros and your other code. Like this, perhaps:
/* X(pin_name, pin_nb) */
#define CPLD_GPIOs(gen) \
X(Pin0, 0, gen) \
X(Pin1, 1, gen) \
X(Pin2, 2, gen) \
X(Pin3, 3, gen)
// Generates the wanted function names:
#define GPIO_ON(pin_name, pin_nb) SetOn_GPIO##pin_name
#define X(pin_name, pin_nb, gen) \
static void gen(pin_name, pin_nb) (void) { \
SetOn_GPIOpins(pin_nb);\
}
CPLD_GPIOs
#undef X
// ...
void some_function(void) {
GPIO_ON(pin_name, pin_nb)();
}
But note well that although this technique might have other applications, such as to generating multiple sets of functions with the same set of X macros, it just kicks the can down the road with respect to the specific objective you described. You can rely on the name-generator macro to produce the same names for function declarations and function calls, but you still have the problem that the X macro can be modified to generate function declarations with different names.

Using our trusty Boost.Preprocessor rocket launcher, this is preatty easy:
#include <boost/preprocessor/tuple/rem.hpp>
#include <boost/preprocessor/control/if.hpp>
#include <boost/preprocessor/comparison/equal.hpp>
#define X_SELECT_PIN(pin_nb, selected_pin_nb, ...) \
BOOST_PP_TUPLE_REM_CTOR(BOOST_PP_IF( \
BOOST_PP_EQUAL(pin_nb, selected_pin_nb), \
(__VA_ARGS__), \
() \
))
// Usage
#define X(pin_name, pin_nb)\
X_SELECT_PIN(pin_nb, 2, SetOn_GPIO##pin_name (void);)
CPLD_GPIOs
#undef X
This uses BOOST_PP_IF to expand your pattern only for the selected pin. The added parentheses and BOOST_PP_TUPLE_REM_CTOR are there to protect the macro from expansions containing commas.

X-macros: how to make the list of variables compile-time configurable?

I have code similar to
#define LIST_OF_VARIABLES \
X(value1) \
X(value2) \
X(value3)
as explained in https://en.wikipedia.org/wiki/X_Macro
Now I have the need to make the LIST_OF_VARIABLES configurable at compile time
So it could effectively be e.g.
#define LIST_OF_VARIABLES \
X(default_value1) \
X(cust_value2) \
X(default_value3)
or e.g.
#define LIST_OF_VARIABLES \
X(default_value1) \
X(default_value2) \
X(cust_value3)
depending on some macros previously defined. The LIST_OF_VARIABLES is long and the customizations are relatively small. I would not like to copy the long list for each customization, because that will cause maintenance issues (the DRY principle https://en.wikipedia.org/wiki/Don%27t_repeat_yourself). As a matter of fact the LIST_OF_VARIABLES should be in one file and the
customizations elsewhere (either another file or just -D options in the Makefile)
In pseudo-code I was thinking of something like
#define X(arg) \
#ifdef CUST_##arg \
Y(CUST_##arg) \
#else \
Y(DEFAULT_##arg) \
#endif
And then use the X-macros under the name Y.
But of course that does not work, because a macro cannot contain preprocessor
directives.
What would be a way to achieve this? C is a must (no templates or Boost
macros), gcc specific solutions are acceptable.

I think that what you have to do is along the lines of:
#ifdef USE_DEFAULT_VALUE1
#define X_DEFAULT_VALUE1 X(default_value1)
#else
#define X_DEFAULT_VALUE1 /* omitted */
#endif
#ifdef USE_DEFAULT_VALUE2
#define X_DEFAULT_VALUE2 X(default_value2)
#else
#define X_DEFAULT_VALUE2 /* omitted */
#endif
#ifdef USE_DEFAULT_VALUE3
#define X_DEFAULT_VALUE3 X(default_value3)
#else
#define X_DEFAULT_VALUE3 /* omitted */
#endif
#ifdef USE_CUST_VALUE1
#define X_CUST_VALUE1 X(cust_value1)
#else
#define X_CUST_VALUE1 /* omitted */
#endif
#ifdef USE_CUST_VALUE2
#define X_CUST_VALUE2 X(cust_value2)
#else
#define X_CUST_VALUE2 /* omitted */
#endif
#define LIST_OF_VARIABLES \
X_DEFAULT_VALUE1 \
X_DEFAULT_VALUE2 \
X_DEFAULT_VALUE3 \
X_CUST_VALUE1 \
X_CUST_VALUE2 \
You then need to define USE_DEFAULT_VALUE1 etc as required for the specific configuration you are after.
As long as you always need the items in the same order, this is sufficient. If you need them in different orders, then you conditionally define LIST_OF_VARIABLES in the different sequences.

Answering myself.
With help of the comments I came up with a solution that works and meets most
requirements I had mentioned
With the "main code"
$cat main.c
#ifndef VALUE1
#define VALUE1 value1
#endif
#ifndef VALUE2
#define VALUE2 value2
#endif
#ifndef VALUE3
#define VALUE3 value3
#endif
#define LIST_OF_VARIABLES \
X(VALUE1) \
X(VALUE2) \
X(VALUE3)
and a customization file like
$cat cust1
-DVALUE2=value2cust
the code can be compiled using (GNUmake pseudo syntax)
$(CC) $(CFLAGS) $(shell cat cust1) main.c
Actually having the extra indirection with every value defined on a single
line is good, because it allows commenting the values. That would not have
been possible with the continuation lines in the single LIST_OF_VARIABLES macro.
Edit: Not true. A COMMENT(foo) macro expanding to nothing would have solved that issue, too. (Credit: Got the idea from the answer posted by #Jonathan Leffer.)
However the approach does not yet meet the following requirements I hadn't mentioned
no ugly boilerplate code (all these #ifndef lines are not really nice)
customization should also make it possible to drop default values from the
list altogether or add completely new values (yes, this could probably be
done with some ugly dummy code already now)
So not really satisfied yet with my own answer. Need to think about the
approach from the Dr. Dobbs article a bit more, maybe that can be used.
Open for better answers.

Given further context, it appears you want to be able to cherry pick individual values from your list at compile time. I think you might be interested in a preprocessor switch, which can accomplish what you're using preprocessor conditionals for with a lot less boilerplate.
Generic preprocessor switch
Here's a brief framework:
#define GLUEI(A,B) A##B
#define GLUE(A,B) GLUEI(A,B)
#define SECONDI(A,B,...) B
#define SECOND(...) SECONDI(__VA_ARGS__,,)
#define SWITCH(NAME_, PATTERN_, DEFAULT_) SECOND(GLUE(NAME_,PATTERN_), DEFAULT_)
SWITCH macro usage
Invoke SWITCH(MY_PREFIX_,SPECIFIC_IDENTIFIER,DEFAULT_VALUE) to expand everything that is not a matching pattern to DEFAULT_VALUE. Things that are a matching pattern can expand to whatever you map them to.
To create a matching pattern, define an object like macro called MY_PREFIX_SPECIFIC_IDENTIFIER, whose replacement list consists of a single comma followed by the value you want the SWITCH to expand to in this case.
The magic here is simply that SWITCH builds a hidden token, giving it a chance to expand (well, in this implementation SECOND's indirection is also significant), and inject a new second argument to SECOND if it's defined. Nominally this new token isn't defined; in such cases, it simply becomes the first argument to SECOND, which just discards it, never to be seen again.
For example, given the above macros:
#define CONTRACT_IDENTIFIER_FOR_DEFAULT , overridden_id_for_default
#define CONTRACT_IDENTIFIER_FOR_SIGNED , overridden_id_for_signed
SWITCH(CONTRACT_IDENTIFIER_FOR_, DRAFT , draft )
SWITCH(CONTRACT_IDENTIFIER_FOR_, DRAWN , drawn )
SWITCH(CONTRACT_IDENTIFIER_FOR_, PROOFED , proofed )
SWITCH(CONTRACT_IDENTIFIER_FOR_, DELIVERED , delivered )
SWITCH(CONTRACT_IDENTIFIER_FOR_, SIGNED , signed )
SWITCH(CONTRACT_IDENTIFIER_FOR_, FULFILLED , fulfilled )
SWITCH(CONTRACT_IDENTIFIER_FOR_, DEFAULT , default )
...will expand to:
draft
drawn
proofed
delivered
overridden_id_for_signed
fulfilled
overridden_id_for_default
Decorated X Macros
Assuming you wish to give your values names, and simply replace cherry picked values from the command line, you can make use of SWITCH to do something like this:
#define VARVALUE(N_,V_) SWITCH(VALUE_FOR_, N_, V_)
#define LIST_OF_VARIABLES \
X(VARVALUE(value1, default_value1)) \
X(VARVALUE(value2, default_value2)) \
X(VARVALUE(value3, default_value3))
The VARVALUE macros will be applied first in this form. To override a specific value, you can define your pattern matcher using either a #define:
#define VALUE_FOR_value2 , custom_value2
...or on the command line/makefile:
CFLAGS += -DVALUE_FOR_value2=,custom_value2
Disable/insertion using switch macro
To support disabling individual items safely, nest two switches and add an EAT macro to catch the entry:
#define EAT(...)
#define SELECT_ITEM_MACRO_FOR_STATE_ON , X
#define X_IF_ENABLED(N_, V_) \
SWITCH(SELECT_ITEM_MACRO_FOR_STATE_, SWITCH(ENABLE_VALUE_, N_, ON), EAT) \
(SWITCH(VALUE_FOR_, N_, V_))
#define LIST_OF_VARIABLES \
X_IF_ENABLED(value1, default_value1) \
X_IF_ENABLED(value2, default_value2) \
X_IF_ENABLED(value3, default_value3)
Just as before, individual macros can be overridden using VALUE_FOR_valuex pattern macros, but this also allows disabling items using ENABLE_VALUE_valuex macros, which can be set to anything but ,ON to disable that item.
Similarly, one way to add support for inserting values is to flip the idea:
#define ADD_ITEM_MACRO_FOR_STATE_EAT , EAT
#define X_IF_ADDED(N_) \
SWITCH(ADD_ITEM_MACRO_FOR_STATE_, SWITCH(VALUE_FOR_, N_, EAT), X) \
(SECOND(GLUE(VALUE_FOR_,N_)))
#define LIST_OF_VARIABLES \
X_IF_ENABLED(value1, default_value1) \
X_IF_ENABLED(value2, default_value2) \
X_IF_ENABLED(value3, default_value3) \
X_IF_ADDED(value4) \
X_IF_ADDED(value5) \
X_IF_ADDED(value6)
...this allows you to define VALUE_FOR_value4 as a a pattern macro, but by default will expand to nothing.
Summary
The framework supporting setting, removing, or inserting values winds up being:
#define GLUEI(A,B) A##B
#define GLUE(A,B) GLUEI(A,B)
#define SECONDI(A,B,...) B
#define SECOND(...) SECONDI(__VA_ARGS__,,)
#define SWITCH(NAME_, PATTERN_, DEFAULT_) SECOND(GLUE(NAME_,PATTERN_), DEFAULT_)
#define EAT(...)
#define SELECT_ITEM_MACRO_FOR_STATE_ON , X
#define X_IF_ENABLED(N_, V_) \
SWITCH(SELECT_ITEM_MACRO_FOR_STATE_, SWITCH(ENABLE_VALUE_, N_, ON), EAT) \
(SWITCH(VALUE_FOR_, N_, V_))
#define ADD_ITEM_MACRO_FOR_STATE_EAT , EAT
#define X_IF_ADDED(N_) \
SWITCH(ADD_ITEM_MACRO_FOR_STATE_, SWITCH(VALUE_FOR_, N_, EAT), X) \
(SECOND(GLUE(VALUE_FOR_,N_)))
Given this framework, your list macro would be comprised of a series of X(value), X_IF_ENABLED(name,default_value), and/or X_IF_ADDED(name) values, where:
X(value) can be used to always insert a call to the X macro with value
X_IF_ENABLED(name,default_value) will call X with default_value, allowing you to override the default based on name.
X_IF_ADDED(name) will provide an "empty slot" with name, which will do nothing unless you override that slot.
Overriding slots is done by defining VALUE_FOR_name to expand to ,replacement. Disabling enabled slots is done by defining ENABLE_VALUE_name to expand to ,OFF.
Demo showing change, removal, addition using command line

Asterisk in the argument name with C preprocessor

I want to implement cross-platform build of my DLL with mingw32/VC.
At the moment everything is perfect with mingw side. However I have to wrap several things in macro for VC (it is built as /TC), for example:
void __attribute__((fastcall)) do1 ( A*, B , C, D );
bool __attribute__((fastcall)) ( *do2 ) ( E*, F );
The first one is simple, just a macro:
#ifdef __MINGW32__
#define __FASTCALL__ __attribute__((fastcall))
#elif _MSC_VER
#define __FASTCALL__ __fastcall
#else
#error "unsupported compiler"
#endif
The problem comes with the second one. Calling convention with a function pointer should looks like
bool ( __fastcall *do2 ) ( E*, F );
I tried the following macro (I skipped ifdef part):
#define __FASTCALLP__(func) (__attribute__((fastcall))(*##func))
#define __FASTCALLP__(func) (__fastcall *##func)
or if pass function name with asterisk:
#define __FASTCALLP__(func) (__attribute__((fastcall))(##func))
#define __FASTCALLP__(func) (__fastcall ##func)
Both failed with
error: pasting "*" and "function_name" does not give a valid
preprocessing token
May I wrong at my approach at all? Or I have to ifdef the whole code blocks or separate it to different files?

The problem is with the Concatenation-Operator ##. It will produce a new preprocessor token by concatenating the left- and right-hand-side, which does not exists (*do2 is no defined token)
Simply omit it and write like this (omitting #ifdefs):
#define __FASTCALL__(func) (__attribute__((fastcall))(func))
#define __FASTCALL__(func) (__fastcall func)
and use like this:
bool __FASTCALL__(do1)(A*, B , C, D);
bool __FASTCALL__(*do2)(E*, F);

Resources