/*
#include <X11/Xlib.h>
#include <X11/Xlibint.h>
#include <X11/Xproto.h>
#include <X11/Xatom.h>
#include <X11/extensions/Xrandr.h>
#include <X11/extensions/Xrender.h>     /* we share subpixel information */

#include <stdio.h>

#include "/opt/xorg/include/X11/Xlib.h"
#include "/opt/xorg/include/X11/Xlibint.h"
#include "/opt/xorg/include/X11/Xproto.h"
#include "/opt/xorg/include/X11/Xatom.h"
#include "/opt/xorg/include/X11/extensions/Xrandr.h"
#include "/opt/xorg/include/X11/extensions/Xrender.h"     /* we share subpixel information */

#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <math.h>

int main(int argc, char *argv[])
{	
	char* display_name = "default";
	int screen = 0;
	
	Display *dpy = XOpenDisplay(display_name);
	Window root = RootWindow (dpy, screen);
	
	XRRScreenResources *sr = XRRGetScreenResources ( dpy, root );
	XRROutputInfo *output = XRRGetOutputInfo(dpy, sr, sr->outputs[0]);
	
	sprintf("\nScreen name: %s \n", output->name);
	
	return 0;
}


and the output:

/tmp/ccUusm2q.o: In function `main':
tmp.c:(.text+0x26): undefined reference to `XOpenDisplay'
tmp.c:(.text+0x5a): undefined reference to `XRRGetScreenResources'
tmp.c:(.text+0x7b): undefined reference to `XRRGetOutputInfo'
collect2: ld returned 1 exit status