I have two .cpp files and one .h file in my current project, here's the source:

main.cpp

menu.cpp

dialog.h

It SHOULD compile right, right? Except I'm getting errors that say all of the menus and the_dialog are being declared multiple times. Shouldn't the lines:

#ifndef DIALOG_INF_H
#define DIALOG_INF_H

prevent this?

They have to be declared in a .cpp file. Include guards can guard against some things, but not this.

How do I do that, though?

Now I have:

dialog.h

#ifndef DIALOG_INF_H
#define DIALOG_INF_H

int NewMap();

MENU file_child[5];
MENU edit_child[3];
MENU about_child[2];
MENU main_menu[3];

DIALOG the_dialog[4];

#endif

and the dialog.cpp file:

The other two .cpp files (menu.cpp and main.cpp) are unmodified, but I still get the same errors.

Add the word 'extern' to the variable definitions in your header files.

extern MENU file_child[5];
extern MENU edit_child[3];
// etc ...

Doesn't that also mean adding the type identifier to the .cpp file?

MENU file_child[5] = ...
MENU edit_child[3] = ...
//etc ...

extern MENU file_child[5]; // incorrect
extern MENU edit_child[3]; // incorrect

extern MENU file_child[]; // correct
extern MENU edit_child[]; // correct

MENU file_child[5] = ...
MENU edit_child[3] = ...
//etc ...

The declaration is made in one of the .cpp files, and all the others include the .h file that has the extern definitions.

The former is perfectly correct (as is the latter). Putting the values like that even helps the compiler, in some situations.

That said, you generally don't put the size of the array in MENU or DIALOG arrays, since they're NULL terminated anyway, it makes increasing or decreasing the size easier, and the benefits aren't too useful when dealing with them. There's nothing wrong with it of course, it's just not something I see done.

Oh? I thought it counted as a multiple declaration if more than one file includes that header?

Not as long as it's declared extern. Putting in the array size just lets the compiler know how big the array is (without it, things like sizeof(file_child) won't work).

I wrote about this about a week ago... Read up!

I'm still a little bit confused, as I've never used extern before. I get it, but it's still not working.

main.cpp has remained unchanged.

dialog.h is:

and dialog.cpp is:

And yet I am still getting multiple definition errors.

Also, should I include allegro.h and agup.h in all the .cpp files, or just in the dialog.h, since dialog.h is included in all the .cpp files, doesn't that mean allegro is too? Or would it be better form to just include it in all the files it's used in, even if it was already included by dialog.h?

You can include allegro.h and agup.h in as many or as few places as you would like, thats the beauty of headers.

I can't see offhand what else is wrong, here are a few comments on stuff though:

extern int NewMap();

Its not really important, but extern is assumed for all function definitions. If you wanted to sound smart in front of C geeks you'd want to drop the explicit usage of the word here.

You also never implement the NewMap function in dialog.cpp, is there reason for this?

Also IIRC your MENU lists should end with a NULL instance, like the dialog does. Aka:

MENU main_menu[] =
{
   /*   (text)     (proc)   (child)         (flags)    (dp) */
      { "&File",    NULL,    file_child,     0,         NULL },
      { "&Edit",    NULL,    edit_child,     0,         NULL },
      { "&About",   NULL,    about_child,    0,         NULL },
      { NULL }
};

However, I can't see any multiple definition errors in your code. Could you paste your exact compiler command and the resulting errors. Its important that all this information is copied and pasted exactly (in all its jargony glory).

NewMap() was never implemented because I was going to write the function, but I got all these multiple definition errors and haven't gotten around to it yet. I removed the declaration from my source code for now just for less clutter while we work this out.

So once again, here is all the source + errors:

dialog.h:

main.cpp:

dialog.cpp:

And the errors:

Usually, when I double click an error in Dev-Cpp, it highlights the line where the error occurs. Unfortunately it is not taking me to the first definitions.

Yes this is because it does not know where they are. Did you do a full recompile?

Also, the compile command itself would be helpful, you can get it by going to the "Compile Log" tab and selecting everything in that textbox.

**
To do a full recompile click this button:

You can also hit control + F11.
_{** edited in later}

I can't believe I didn't rebuild the project. It works now.

Thanks for the help~

assumed for function declarations

Ah right, I always mix up those two words:P