Running X11 Applications on macOS

Running X11 Applications on macOS

[cml_media_alt id='2597']cpc-startup[/cml_media_alt]

X11R6 Basics

Hello World Basic Programming Knowledge about X11

If you want to run for example 2D vector application like InkScape ( on your Mac you need to install X11.

How to install X11R6 (and InkScape) on your Mac

  1. Download XQuarz here:
  2. Install it
  3. Logout and login again to make X11 active
  4. Put InkSapce App in Applications folder
  5. If asked for permission "from a unsigned developer" to go /Applications folder, right click, choose "open"

(Read more on that here:



Where is X11R6?





Sample X11 program

  * Simple Xlib application drawing a box in a window.
  * gcc input.c -o output -lX11
/* /1/ */
#include <X11/Xlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
    Display *display;
    Window window;
    XEvent event;
    char *msg = "Hello, World!";
    int s;

    /* /2/ some basic X11 setup */
    /* open connection with the server */
    display = XOpenDisplay(NULL);
    if (display == NULL)
        fprintf(stderr, "Cannot open display\n");
    s = DefaultScreen(display);
    /* create window */
    window = XCreateSimpleWindow(display, RootWindow(display, s), 10, 10, 200, 200, 1,
                           BlackPixel(display, s), WhitePixel(display, s));
    /* select kind of events we are interested in */
    XSelectInput(display, window, ExposureMask | KeyPressMask);
    /* map (show) the window */
    XMapWindow(display, window);
    /* /3/ event loop */
    for (;;)
        XNextEvent(display, &event);
        /* /4/ draw or redraw the window */
        if (event.type == Expose)
            XFillRectangle(display, window, DefaultGC(display, s), 20, 20, 10, 10);
            XDrawString(display, window, DefaultGC(display, s), 50, 50, msg, strlen(msg));
        /* /5/ exit on key press */
        if (event.type == KeyPress)
    /* /6/ close connection to server */
    return 0;


/1/ We use X11/Xlib.h basic X11 lib here. #include <X11/Xlib.h>

/2/ Some basic X11 setup, create a X11 window, etc.

/3/ As you can can see, everything interactive is within a so called event loop. It loops forever until something happens: An event.

/4/ Check for event

/5/ Event for exit (break) the event loop, which terminates the event loop, and ...

/6/ ... finally closes the created X window



gcc main.c 
main.c:6:10: fatal error: 'X11/Xlib.h' file not found
#include <X11/Xlib.h>
1 error generated.



Where is Xlib.h?

$ find /usr/ -name "*Xlib.h"

-> So add /usr/X11R6/include/ to your include path (-I):



List undefined (-u) symbols:

$ nm   main.o
 U _XCloseDisplay
 U _XCreateSimpleWindow
 U _XDrawString
 U _XFillRectangle
 U _XMapWindow
 U _XNextEvent
 U _XOpenDisplay
 U _XSelectInput
 U ___stderrp
 U _exit
 U _fprintf
 0000000000000000 T _main
 U _strlen


These Xnnnn functions like XCloseDisplay are X11 functions pointing to X11R6 libs because they are implemented there within the X11 libs.


X11 libs are in /usr/X11R6/lib so add -L Library search path to it (/usr/X11R6/lib) and the library itself (X11) like so:

$ gcc -L/usr/X11R6/lib -lX11 -I/usr/X11R6/include/ main.c



A Makefile could look like this:

## -- just for compiling, C needs the path to the .h files
X11_INC_PATH  = -I/usr/X11R6/include/

## -- library
X11_LIBS_PATH = -L/usr/X11R6/lib/
X11_LIBS      = -lX11

default:    main

main:   main.c
    gcc -Wall $(X11_INC_PATH) $(X11_LIBS_PATH) $(X11_LIBS)  main.c -o main

#    rm -r main.o main


$ make



Which shared libraries are used / linked to my executable? (otool, ldd)

An a Mac, otool is what ldd is on Linux.

$ otool -L ./main
 /opt/X11/lib/libX11.6.dylib (compatibility version 10.0.0, current version 10.0.0)
 /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1225.1.1)



Run it!

$ ./main

[cml_media_alt id='2586']Screen Shot 2015-11-03 at 12.02.42[/cml_media_alt]

I replaced KeyPress to KeyRelease to that I can take a screenshot.

if (event.type == KeyRelease)

More on that, see


Ported CPC 464 for X11 on OS X:

[cml_media_alt id='2597']cpc-startup[/cml_media_alt]


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