Question

I came across this when I was compiling a simple program:

 #include <X11/Xlib.h>
 #include <stdio.h>
 #include <stdlib.h>

 Display* display;

 int main(){
     display = XOpenDisplay("");
     if (display == NULL) {
         printf("Cannot connect\n");
         exit (-1);
     }
     else{
         printf("Success!\n");
         XCloseDisplay(display);
     }
  }

FYI, I have xQuartz installed.
I compile this program with “g++ -o ex ex.cpp -L/usr/X11R6/lib -lX11” command.

Answer 1

you need to compile with:

g++ -o ex ex.cpp -I/usr/X11R6/include -L/usr/X11R6/lib -lX11

the X11 headers are installed with xQuartz, but you need to reference them explicitly

If you install xQuartz it installs into /opt/X11, and /usr/X11 and /usr/X11R6 are symlinks to this location