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Ckath/x.c

Last active September 30, 2025 15:07
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x output loopenings, expected to error at end, not before
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x.c
/* compile: gcc -o x x.c -lXrandr -lX11 */
#include <stdio.h>
#include <X11/Xlib.h>
#include <X11/extensions/Xrandr.h>
int main(void) {
Display *dpy = XOpenDisplay(NULL);
if (!dpy) {
fprintf(stderr,"failed to open display\n");
return 1;
}
Window w = DefaultRootWindow(dpy);
XRRScreenResources *sr = XRRGetScreenResources(dpy, w);
printf("looping to i < noutput, this shouldn't error:\n");
for (int i = 0; i < sr->noutput; ++i) {
XRROutputInfo* oinf = XRRGetOutputInfo(dpy, sr, sr->outputs[i]);
if (oinf) {
printf("name: %s, connected: %s\n", oinf->name,
oinf->connection == RR_Connected ? "yes" : "no");
}
XRRFreeOutputInfo(oinf);
}
printf("\nthis should error:\n");
XRROutputInfo* oinf = XRRGetOutputInfo(dpy, sr, sr->outputs[sr->noutput]);
if (oinf) {
printf("name: %s, connected: %s\n", oinf->name,
oinf->connection == RR_Connected ? "yes" : "no");
}
printf("reached end (this doesnt happen on X11)\n");
XRRFreeOutputInfo(oinf);
XRRFreeScreenResources(sr);
XCloseDisplay(dpy);
return 0;
}
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Ckath commented Sep 29, 2025

expected output

looping to i < noutput, this shouldn't error:
name: DisplayPort-1, connected: yes
name: DisplayPort-0, connected: yes
name: DisplayPort-2, connected: yes
name: HDMI-A-0, connected: yes
name: DVI-D-0, connected: no
name: VGA-1-1, connected: yes

this should error:
X Error of failed request:  BadRROutput (invalid Output parameter)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  9 (RRGetOutputInfo)
  Serial number of failed request:  18
  Current serial number in output stream:  18

allegedly possibly wayland (xwayland?) does not behave like this causing a certain launcher to not die on wayland when they clearly messed something up in their XRRGetOutputInfo call

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