stderr output from gnome-shell

[John Frankish <john frankish outlook com>]

I've been trying to get stderr messages from gnome-shell-3.16.2.

if I change src/main.c line 400 to read:

int
main (int argc, char **argv)
{
  freopen("/tmp/mystderr.txt", "w", stderr);
  GOptionContext *ctx;
  ...

I expected to get JS LOG (I added "log('main.js start ');" to js/ui/main.js)
and JS ERROR messages, but all I get is an empty file /tmp/mystderr.txt

As a test, I modified things to read:

freopen("/tmp/mystderr.txt", "w", stdout);
printf("This text is redirected to mystderr.txt\n");

..but again, all I get is an empty file.

Is there a trick to this? How do I get stderr output from gnome-shell

Regards
John