Problems with variadic macros in C
- by imikedaman
Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2:
bool func1(bool tmp) { return false; }
void func2(bool tmp, bool tmp2) {}
#define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__)
int main() {
// this compiles
CALL(func2, CALL(func1, false), false);
// this fails with: Implicit declaration of function 'CALL'
CALL(func2, false, CALL(func1, false));
}
That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly?
Additional information:
If I remove the ## before _VA_ARGS_, and do something like this:
bool func2(bool tmp, bool tmp2) { return false; }
#define CALL(func, tmp, ...) func(tmp, __VA_ARGS__)
int main() {
CALL(func2, false, CALL(func2, false, false));
}
That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )
