XCreateSimpleWindow causing segfault

[faint sluice]

Does anyone know why this is causing a segfault?

#include <X11/Xlib.h>

int main() {
    Display *display = XOpenDisplay(NULL);
    Window w = XCreateSimpleWindow(display, DefaultRootWindow(display), 0, 0, 400, 400, 1, 0, 0);
}

[tulip solar]

xopendisplay can fail and return null -> segfault?

also needs to call xclosedisplay

[faint sluice]

The problem is I see no reason that this would be failing.

[tulip solar]

What's your DISPLAY env var?

@faint sluice

[faint sluice]

what's that?

[tulip solar]

Your environment variable called DISPLAY

[tulip solar]

Did you write this code yourself?

Display *XOpenDisplay(char *display_name);
display_name Specifies the hardware display name, which determines the display and communications domain to be used. On a POSIX-conformant system, if the display_name is NULL, it defaults to the value of the DISPLAY environment variable.

-> The env var is not set in your case -> It defaults to the empty string -> That display doesn't exist -> XOpenDisplay returns NULL

https://www.x.org/releases/X11R7.5/doc/man/man3/XOpenDisplay.3.html

Sounds like ChatGPT code

[faint sluice]

I did, though it's very simplified in order to find the cause of my problem

[tulip solar]

Passing NULL into XOpenDisplay is your issue

[faint sluice]

I should mention that this code worked before, and without any change that I can remember, it stopped working. It used to be nullptr there (which also doesn't work now), but I changed it to NULL after seeing that in a tutorial.

[tulip solar]

Probably because of a change in your environment variables?

[faint sluice]

how can I set that environment variable, and how can I figure out what to set it to?

[tulip solar]

https://www.google.com/search?q=linux+set+environment+variable

If you're running one instance of X server then the display name is probably :0

[faint sluice]

ok, found that it is indeed :0

[tulip solar]

You could just pass in ":0" into XOpenDisplay as well

[faint sluice]

that still segfaults, so it's probably some other env var that's causing the problem?

[tulip solar]

Try printing out the return value

[faint sluice]

of XOpenDisplay?

it prints 0

(passing ":0" into it)