Conditional X-MACROs to align ENUMs and String - c

Question

I have a list of enums:
typedef enum {
ENUM1,
ENUM2,
#if FLAG
ENUM3,
#endif
} enum_var_t;
And a corresponding list of strings to align:
typedef struct { char[50] name; int val; } name_val_map_t
name_val_map_t name_val_map_table[] = {
{.name="string1", .val=ENUM1},
{.name="string2", .val=ENUM2},
#if FLAG
{.name="string3", .val=ENUM3},
#endif
};
FLAG is a build flag, and is either 0, or 1.
I am trying to use X-Macros to align these according to an answer here:
#define IF(cond, foo) IF_IMPL(cond, foo)
#define IF_IMPL(cond, foo) IF_ ## cond (foo)
#define IF_0(foo)
#define IF_1(foo) foo
#define var_list \
X(ENUM1, "string1"), \
X(ENUM2, "string2"), \
IF(FLAG, X(ENUM3, "string3")), \
#define X(ENUMVAL, ...) ENUMVAL
typedef enum {
var_list
}
#undef X
#define X(ENUMVAL, NAME) {.name = NAME, .val = ENUMVAL}
name_val_map_t name_val_map_table = {
var_list
}
This leads to an error which says I'm passing more arguments to the IF macro than declared. I presume it is treating the comma inside the X(ENUM3, "string3") as an argument separator for IF.
I tried encapsulating the X() call with braces and removing the braces from IF_IMPL, but that didn't work either. If I try expand the argument list in IF() using ..., and VA_ARGS, I get expected expression errors. I'm trying to avoid using a def file as this makes my file unreadable. Some solution like I was trying would be perfect to avoid code replication, and for readability. Any pointers would be welcome, thanks!

Answer 1

Using variadic macros.
#define IF(cond, foo) IF_IMPL(cond, foo)
#define IF_IMPL(cond, ...) IF_ ## cond(__VA_ARGS__)
#define IF_0(foo, ...)
#define IF_1(foo, ...) foo, __VA_ARGS__
Test:
//usr/local/bin/tcc -run "$0"; exit $?
#include <stdio.h>
#define FLAG3 1
#define FLAG4 0
#define FLAG5 1
typedef struct { char *name; int val; } name_val_map_t;
#define IF(cond, foo) IF_IMPL(cond, foo)
#define IF_IMPL(cond, ...) IF_ ## cond(__VA_ARGS__)
#define IF_0(foo, ...)
#define IF_1(foo, ...) foo, __VA_ARGS__
#define var_list \
X(ENUM1, "string1") \
X(ENUM2, "string2") \
IF(FLAG3, X(ENUM3, "string3")) \
IF(FLAG4, X(ENUM4, "string4")) \
IF(FLAG5, X(ENUM5, "string5")) \
typedef enum {
#define X(ENUMVAL, str) ENUMVAL,
var_list
#undef X
} enum_var_t;
name_val_map_t name_val_map_table[] = {
#define X(ENUMVAL, NAME) { NAME, ENUMVAL },
var_list
#undef X
{ "sentinel value", 99 }
};
int main(void){
int x =0;
while(name_val_map_table[x].val != 99){
printf("%i, %s\n", name_val_map_table[x].val, name_val_map_table[x].name);
x++;}
return 0;
}
/* output:
0, string1
1, string2
2, string3
3, string5
*/
Another option is to manually create IF_FLAGx( X(bla, bla) ) macros for every case...
See also: macro specialization based on argument in case of MSVC bug.

Answer 2

This seems needlessly complicated. I would simply do this instead:
#if FLAG
#define var_list \
X(ENUM1, "string1") \
X(ENUM2, "string2") \
X(ENUM3, "string3")
#else
#define var_list \
X(ENUM1, "string1") \
X(ENUM2, "string2")
#endif
Full example:
#include <stdio.h>
#define FLAG 1
#if FLAG
#define var_list \
X(ENUM1, "string1") \
X(ENUM2, "string2") \
X(ENUM3, "string3")
#else
#define var_list \
X(ENUM1, "string1") \
X(ENUM2, "string2")
#endif
typedef enum
{
#define X(enum_var, str) enum_var,
var_list
#undef X
ENUM_N
} enum_var_t;
typedef struct
{
char name[50];
int val;
} name_val_map_t;
const name_val_map_t name_val_map_table[] =
{
#define X(enum_var, str) { .name = str, .val = enum_var },
var_list
#undef X
};
int main (void)
{
for(size_t i=0; i<ENUM_N; i++)
{
printf("%d %s\n", name_val_map_table[i].val, name_val_map_table[i].name);
}
}