Thin wrapper around X API calls to query active keyboard layout

getlayout.cpp

// compile with `g++ getlayout.cpp -lX11 -lxkbfile`
// original source: https://gist.github.com/fikovnik/ef428e82a26774280c4fdf8f96ce8eeb
#include <cstdlib>
#include <cstring>
#include <stdexcept>
#include <memory>

#include <X11/XKBlib.h>
#include <X11/extensions/XKBrules.h>

namespace detail {
	template<typename T>
	struct XDeleter {
		void operator()(T* ptr) const noexcept { XFree(ptr); }
	};
}

template<typename AtomT>
using XPtr = std::unique_ptr<AtomT, detail::XDeleter<AtomT>>;

class XDisplay {
private:
	Display* const dpy;

public:
	XDisplay()
		:dpy{ XOpenDisplay(NULL) }
	{
		if(!dpy) throw std::runtime_error{ "Cannot open display" };
	}

	Display* get() const noexcept { return dpy; }

	XkbStateRec xkbGetState(unsigned int device_spec = XkbUseCoreKbd) {
		XkbStateRec state;
		XkbGetState(dpy, device_spec, &state);
		return state;
	}

	XkbDescPtr xkbGetKeyboard(unsigned int which = XkbAllComponentsMask, unsigned int device_spec = XkbUseCoreKbd) {
		return XkbGetKeyboard(dpy, which, device_spec);
	}

	XPtr<char> getAtomName(Atom atom) {
		return XPtr<char>{ XGetAtomName(dpy, atom) };
	}

	std::string getKeyboardLayout() {
		XkbStateRec state = this->xkbGetState();

		XkbRF_VarDefsRec vd;
		std::memset(&vd, 0, sizeof(vd));
		XkbRF_GetNamesProp(this->get(), NULL, &vd);

		char *tok = strtok(vd.layout, ",");

		for (int i = 0; i < state.group; i++) {
			tok = strtok(NULL, ",");
			if (tok == NULL) {
				throw std::runtime_error{ "Keyboard layout lookup error" };
			}
		}

		std::string result{ tok };

		// no better way, source: https://github.com/khurshid-alam/Unity-Settings-Daemon/commit/7135a08b39e17401338232ee3f0309582dd31202
		free(vd.model);
		free(vd.layout);
		free(vd.variant);
		free(vd.options);

		return result;
	}


	XDisplay(const XDisplay&) = delete;
	XDisplay& operator=(const XDisplay&) = delete;

	~XDisplay() noexcept { XCloseDisplay(dpy); }
};


int main() {
	XDisplay dpy;
	auto kbd = dpy.xkbGetKeyboard();
	printf("Layout name: %s\n", dpy.getAtomName(kbd->names->groups[dpy.xkbGetState().group]).get());
	return 0;
}

Note: main() is leaking memory, and I don't know how to fix it.
XDisplay::getKeyboardLayout() doesn't leak, but its resource cleanup is ugly and not exception-safe.

related: sergei-mironov/xkb-switch#30