It will be fine for Windows, because in Window long and unsigned long are always 4 byte. But other systems (for instance, all Linux distros) have long and unsigned long 8 bytes under 64-bit systems. c_ulong makes sure, that it's the correct size on all systems.
Thank you very much, Denis. It was quite confusing to mix extern(C++) and extern(Windows). And I also thank Jakob for syntax specification.
As all your functions are `APIENTRY`, write `extern(Windows):` before them. And use `c_ulong` as analogue of `unsigned long`. So full correct `IBank` interface declaration here:
---
import core.stdc.config: c_ulong;
extern(C++) interface IBank
{
extern(Windows):
const char* getLastError();
const char* getDetail(char* detail);
bool deposit(c_ulong number, double amount);
bool withdraw(c_ulong number, double amount);
double getBalance(c_ulong number);
bool transfer(c_ulong numberFrom, IBank* bankTo, c_ulong numberTo, double amount);
bool transferAccept(IBank* bankFrom, c_ulong numberTo, double amount);
};
---
BTW, it's said in the ABI reference that `unsigned long` must be substituted with `uint`. And it seems to work fine for the data I used in the example.