Problem with extern struct object, in header file. Undefined type.

RHLinuxGUY · 07-23-2006, 07:36 PM

I am having a problem with my program. I am getting an error (shown below) when compiling my game.
I have the struct defined in a seperate file called variables.cpp, along with a global object array.

So it looks like this:

Code:

struct CharObj
{
    //...
}character_obj[128];

While in the header file I made an external reference to it, looks like the following:

Code:

extern struct CharObj character_obj[128];

Yet, when I get the following error when compiling:

Code:

g++ -c -g Char_Movement.cpp
Char_Movement.cpp: In function `void PlayerMove(bool, bool, bool, bool, int)':
Char_Movement.cpp:10: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:10: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:22: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:22: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:34: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:34: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:46: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
Char_Movement.cpp:46: error: invalid use of undefined type `struct CharObj'
space_carnage.h:67: error: forward declaration of `struct CharObj'
make: *** [Char_Movement.o] Error 1

Any suggestions? If need more information, please ask and I should respond right away.

spooon · 07-23-2006, 07:59 PM

did you define "struct CharObj" anywhere that is included by this file?

RHLinuxGUY · 07-23-2006, 08:32 PM

I defined struct CharObj in another file called variables.cpp. I'm thinking you mean did I make an object of this struct right? If so, I did in that same variables.cpp file.

It looks like the following:

// Variables.cpp file

Code:

struct CharObj
{
    //...
}character_obj[128];

// space_carnage.h

Code:

extern struct CharObj character_obj[128];

Obviously the above two pieces of codes from the files exclude all other variables and predecessor files.

I believe I may have misunderstood you, correct me if I am right.

spooon · 07-23-2006, 08:36 PM

Well Char_Movement.cpp needs to know what the hell a "struct CharObj" is, if it appears in its code. So you should put the definition of it, i.e.

Code:

struct CharObj
{
    //...
};

in the header file.

RHLinuxGUY · 07-23-2006, 09:40 PM

Thank you, that works. I have a question though, how would I be able to make an class/struct object global to all files? I already found another way to send data with pointers, but as a future reference, is it possible?

Matir · 07-23-2006, 10:05 PM

If you're going to use a particular struct type in a number of places, it's best to place it in a header file rather than to define a type in a C/CPP file.

For future reference, the following should work as well:

Code:

extern struct CharObj *character_obj;

RHLinuxGUY · 07-23-2006, 11:55 PM

Thank you, I got it now.

Matir · 07-24-2006, 12:01 AM

No problem. Just trying to expose all possible solutions, especially in the hopes that future searchers may find it useful.