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--- c.h
#ifndef C_H
#define C_H
#define FOO_ID(x) (x*3)
int twice(int i);
#endif
--- c.c
int twice(int i) { return i * 2; }
--- foo.dpp
#include "c.h"
void main() {
import std.stdio;
writeln(twice(FOO_ID(5)));
}