What I mean is normally solved with using an enum:

enum AddrFam { af_unspec, af_inet, af_inet6 };
void myfunc(AddrFam) {} // e.g. for lower case constants
void myfunc(int) {}     // e.g. for upper case constants

int main() {
    myfunc(af_unix);
    return 0;
}

This results with the compiler error:

error: ‘af_unix’ was not declared in this scope
 15 |     myfunc(af_unix);
    |            ^~~~~~~

That is as expected. But how can I achieve the same with the predefined upper case constants? I cannot use the already predefined constants AF_UNSPEC, AF_INET, AF_INET6 in an enum so

myfunc(AF_UNIX);

compiles without error.