Box2D Forums

Hi,

I just learned GDI in C++ and the first thing I want to make is a simple physics sandbox. I have chosen Box2D for this because it seems lightweigth and easy
However, I'm new to including other projects in my project, so this is what I did to include Box2D:

I copied the Source directory from the zip to my project directory (Visual Studio 2008/Projects/Physics)
Then I make a file called "Box2D.h" and put this in it:



And then I added this to my main.cpp file:





However, when I add the last line it stops compiling with this error:



I have no idea what this means and I want to use Box2D so badly Does anyone have a solution?

Unresolved external symbol means that the compiler knows there's a function/method named like the one you are trying to call, but the linker can't find where the function/method is defined, ie where the "contents" of it are.

Box2D is compiled into a "statically linked library", meaning that when Box2D is compiled a .lib file is created. This .lib does nothing on its own, it needs to be linked into another project (yours) which calls functions/methods inside it. The .lib will become a part of the project's final .exe so you won't need the .lib after that. (Another way is to use a Dynamically Linked Library, but Box2D isn't configured for that.)

The compiler and linker will however need to know what's inside the library when compiling a project which uses it. For this we use a header (Box2D.h) containing all the definitions of the functions/methods/etc in the library.
This is also included in the sources (include folder) so you shouldn't have to create it yourself. It doesn't need to be included into your project, neither does the sources, it's usually easier to just keep them in an easy to remember location.

If you don't have a .lib file you need to open the Box2D solution and compile the Engine project in it. This should generate the .lib. (The TestBed, freeglut, glui and HelloWorld projects are not required by Box2D itself.)

All you have to do to your source to include Box2D is #include "Box2D.h" in your main.cpp.

To get it to actually compile/link you need to tell the compiler where it can find the header, and the linker where it can find the library. You can either do this globally in Visual Studio's preferences, or for an individual project at it's (very similar) preference window. Visual Studio won't however know exactly which .lib file it should include from the path you specified, so you need to add box2d.lib (just the name, not path) as a dependancy or "additional library" in your project's linker settings. VS will then know that it should start looking for box2d.lib when linking, find it in the include/library path you specified, and notice that it contains the definitions of the functions/methods from Box2D.h.


Sorry if this is all a bit confusing at first, I tried to keep it fairly simple but yet detailed enough to not leave you with lots of unanswered questions at every step...

Nevermind, I got it all working thanks to you

Click C/C++ to set the Compiler path (to where the Box2D header is), somewhere at the top there's a list to which you can add entries. I'm on Linux and don't remember exactly what it looks like.

Click Linker to set the paths for the linker (folder where the .lib is), works the same as the list mentioned above.
There is also a field for "additional dependancies" or similar there. Just type in "box2d.lib".

Hi! I just wanted to say thanks to TwoD, your post was very helpful to me!!