Class Redefinition error

Hello,
I have a class in ClassManager.h declared as follows:

Code:

---

#include "DebugWriter.h"

class OutputManager : public DebugWriter {

---

The class uses DebugWriter class defined in DebugWriter.h.
The compiler runs fine, and all intended effects of DebugWriter is working. Now I have a new classes defined as follows:

Code:

---

#include "DebugWriter.h"

class BMManager : public DebugWriter {

---

Once added I have class DebugWriter redefiniton error. I got rid of the error after adding #ifndef.
Question:
I am trying to understand how the compiler runs the pass. I am thinking it needs to compile
step 1: compiler compiles OutputManager.cpp to OutputMaqnger.o and does it that by loading up OutputManger.cpp, then loads up OutManager.h and then loads DebugWriter.h.

Step 2:
compiler compiles BMManager.cpp to BMManager.o and does it that by loading up BMManger.cpp, then loads up BMManager.h and then loads DebugWriter.h.


Step 3: The .o objects is linked to become .exe


Question:
In step 2, the compiler should have no prior knowledge that DebugWriter class is defined. Why would it says redefined??

Quote:

---

Originally Posted by derder

I got rid of the error after adding #ifndef.

---

Yes, always use inclusion guards when writing headers.

Quote:

---

Originally Posted by derder

In step 2, the compiler should have no prior knowledge that DebugWriter class is defined. Why would it says redefined??

---

It shouldn't. However, since it did say that, and since you are more likely to have made a mistake, you probably forgot to account for a multiple inclusion of DebugWriter.h through another header that was included.