How can I generate a list via the C preprocessor (cpp)?

Question

I would like to do something like the following:

F_BEGIN

F(f1) {some code}
F(f2) {some code}
...
F(fn) {some code}

F_END

and have it generate the following

int f1() {some code}
int f2() {some code}
...
int fn() {some code}

int (*function_table)(void)[] = { f1, f2, ..., fn };

The functions themselves are easy. What I can't seem to do is to keep track of all of the names until the end for the function_table.

I looked at this question and this question but I couldn't get anything to work for me. Any ideas?

Answer 1

The normal way of doing this with the preprocessor is to define all the functions in a macro that takes another macro as an argument, and then use other macros to extract what you want. For your example:

#define FUNCTION_TABLE(F) \
    F(f1, { some code }) \
    F(f2, { some code }) \
    F(f3, { some code }) \
:

    F(f99, { some code }) \
    F(f100, { some code })

#define DEFINE_FUNCTIONS(NAME, CODE)     int NAME() CODE
#define FUNCTION_NAME_LIST(NAME, CODE)   NAME,

FUNCTION_TABLE(DEFINE_FUNCTIONS)
int (*function_table)(void)[] = { FUNCTION_TABLE(FUNCTION_NAME_LIST) };

Answer 2

If you have a C99 complying compiler, the preprocessor has variable length argument lists. P99 has a preprocessor P99_FOR that can do "code unrolling" like the one you want to achieve. To stay close to your example

#define MYFUNC(DUMMY, FN, I) int FN(void) { return I; } 
#define GENFUNCS(...)                                          \
P99_FOR(, P99_NARG(__VA_ARGS__), P00_IGN, MYFUNC, __VA_ARGS__) \
int (*function_table)(void)[] = { __VA_ARGS__ }

GENFUNCS(toto, hui, gogo);

would expand to the following (untested)

int toto(void) { return 0; } 
int hui(void) { return 1; }
int gogo(void) { return 2; }
int (*function_table)(void)[] = { toto, hui, gogo };