Question

I had a working project. After rearranging some code, I tried to recompile my project and then weird things started happening. Have a look at this excerpt from the compiler’s output. I’m compiling from Eclipse on Windows using MinGW G++.

**** Build of configuration Debug for project Pract2 ****

**** Internal Builder is used for build               ****
g++ -O0 -g3 -Wall -c -fmessage-length=0 -omove.o ..\move.cpp
In file included from ..\/game.h:11:0,
                 from ..\/piece.h:10,
                 from ..\/move.h:10,
                 from ..\move.cpp:7:
..\/board.h:18:2: error: 'Piece' does not name a type

board.h, line 18:

Piece* GetPieceAt(int row, int col) const;

Usually when that happens, I just have to add some inclusions I’ve forgotten to do. But I have in fact included piece.h at the top of board.h.

My second thought was that the compiler must have generated an error somewhere in the Piece class that would cause the compiler ignore the existence of the class, which in turn would cause more errors. In that case I’d look at the first compiler error, which I expected would be something about an error in piece.cpp or piece.h. But the first error isn’t about Piece at all, so I looked if Eclipse had marked any errors in piece.cpp or piece.h. Nope, not a red line in sight. I only saw a few of these unexplained yellow markers.

One last thing that I checked was that every header file contained inclusion guards, which they did.

How do I get to the bottom of this error? I’d post code snippets, but then I would probably end up pasting the entire code (which I can’t do) because additional context may be necessary.

Edit: here’s board.h up to line 18. (I’ve left out a big comment, that explains why this block of code is smaller than you’d expect.)

#ifndef BOARD_H_
#define BOARD_H_
#include "piece.h"

class Board {
public:
    // Prototypes for externally defined functions
    Board();
    ~Board();
    void PrintBoard();
    Piece* GetPieceAt(int row, int col) const;

Answer 1

Most likely by “rearranging your code” you created a circular inclusion between board.h and piece.h. Your header files contain include guards that prevent infinite inclusion in such cases, but that will not help the declarations to compile.

Check for circular inclusion and rethink you inclusion strategy accordingly. If you don’t have any circular dependencies between the types, you should be able to eliminate the circular inclusion easily. If you do have the circular dependency between the types, you’ll have to resort to forward declarations for some types. Attempting to include header files in circular fashion will not achieve anything.