Problem including X11 in XCode.

I am using XCode and a library called CImg which uses X11. When I run this program:
include "CImg.h"
using namespace cimg_library;
int main() {
CImg image("snail.bmp");
}

I get these errors:

Undefined symbols: "_XUnlockDisplay", referenced from:
"_XGetVisualInfo", referenced from: cimg_library::CImgDisplay::_assign(unsigned int, unsigned int, char const*, unsigned int, bool, bool)in main.o
"_XStoreColors", referenced from: cimg_library::CImgDisplay::_set_colormap(unsigned long&, unsigned int)in main.o
etc.

I think XCode doesn't know where my X11 is, and to be honest I'm not sure I've installed it correctly. I think it is supposed to be in opt/X11 but I don't see it.
Any idea of how to fix this?

I'm not sure what version of OS X you're using but if you're using Snow Leopard or newer, head over to the XQuartz project and install X11 from there.

vansmith said:

I'm not sure what version of OS X you're using but if you're using Snow Leopard or newer, head over to the XQuartz project and install X11 from there.

Click to expand...

I am using 10.5.8 and have installed XQuartz. I am still getting the same error though. I think it has to do with changing my command line tools in XCode. How do I do this?

I forgot to mention I am using XCode 3.1.4, if that matters.

What you need to do is install the X11 SDK, or Software Development Kit. Don't ask me where to get it, haven't messed with that in a LONG time.

cradom said:

What you need to do is install the X11 SDK, or Software Development Kit. Don't ask me where to get it, haven't messed with that in a LONG time.

Click to expand...

I imagine that a copy is available on Apple's developer download page.