C++ Exception Design Pattern

Question

I'd like to encapsulate Win32 errors (those returned from GetLastError()) in some form of exception class. Rather than having a single Win32 exception, however, I'd like to be able to have a specialized exception catchable for common errors, such as ERROR_ACCESS_DENIED. For example, I'd have classes declared like this: ``` class WindowsException : public std::exception { public: static WindowsException Create(DWORD lastError); //blah }; class ErrorAccessDeniedException : public WindowsException { public: //blah }; ``` However, I'd like the Win32 exception to be responsible for picking the right exception to return. That is, the thrower of the exception should look like: ``` int DangerousMethod() { throw WindowsAPI::WindowsException::Create(GetLastError()); } ``` and the catcher might look like: ``` try { DangerousMethod(); } catch(WindowsAPI::ErrorAccessDeniedException ex) { //Code for handling ERROR_ACCESS_DENIED } catch(WindowsAPI::WindowsException ex) { //Code for handling other ki…

Accepted Answer

Change

```
int DangerousMethod() {
    throw WindowsAPI::WindowsException::Create(GetLastError());
}
```

To

```
int DangerousMethod() {
    WindowsAPI::WindowsException::Throw(GetLastError());
}
```

Meaning, instead of returning the exception then throwing it (which will slice, as you observed), have your helper/factory method throw it directly.

C++ Exception Design Pattern

Solution

Problem