Properly delete GList and identifying the mount point drive (follow-up)

[oneeyeman1 (Igor K)]

Hi, ALL,
I have 2 follow-up questions on the other thread here: Difference between volume and drive - #34 by oneeyeman1.

1. From the get_mounts() documentation:

The returned list should be freed with g_list_free(), after its
elements have been unreffed with g_object_unref()

    for( volumes = volumelist; volumes != NULL; volumes = volumes->next )
        g_object_unref( volumes );
    g_list_free( volumelist );

I presume the code adobe is wrong as it throws an exception
on the g_object_unref().

But I can’t just call g_list_free(), right?

I also tried this:

if( volumelist )
{
    g_list_foreach( volumes, g_object_unref, NULL );
    g_list_free( volumelist );
}

which resulted in

error: invalid conversion from ‘void ()(gpointer)’ {aka ‘void
()(void*)’} to ‘GFunc’ {aka ‘void ()(void, void*)’} [-fpermissive]
66 | g_list_foreach( volumes, g_object_unref, nullptr );
| ^~~~~~~~~~~~~~
| |
| void ()(gpointer) {aka void
()(void*)}
In file included from /usr/include/glib-2.0/glib/ghash.h:36,
from /usr/include/glib-2.0/glib.h:52,
from /usr/include/glib-2.0/gobject/gbinding.h:30,
from /usr/include/glib-2.0/glib-object.h:24,
from /usr/include/glib-2.0/gio/gioenums.h:30,
from /usr/include/glib-2.0/gio/giotypes.h:30,
from /usr/include/glib-2.0/gio/gio.h:28,
/usr/include/glib-2.0/glib/glist.h:139:60: note: initializing
argument 2 of ‘void g_list_foreach(GList*, GFunc, gpointer)’
139 | GFunc func,
| ~~~~~~~~~~~~~~~~^~
make: *** [Makefile:28049: coredll_volumeenum.o] Error 1

2. How do I uniquely identify the mounted volume?

   auto monitor = g_volume_monitor_get();
   GList *volumes, *volumelist;
   // On some systems, partition is mounted hidden by default
   // If “volumelist” comes back as “nullptr”, it is normal behavior
   if( flagsSet & wxFS_VOL_MOUNTED && !( flagsUnset & wxFS_VOL_MOUNTED ) )
   {
   volumelist = g_volume_monitor_get_mounts( monitor );
   for( volumes = volumelist; volumes != NULL; volumes = volumes->next )
   {
   gpointer volume = volumes->data;
   char *name = g_mount_get_name( (GMount *) volume );
   // store the name in some containter
   g_free( name );
   }
   }

doing this will return a very generic name “XXXGB hard drive”.

And so when I later on loop thru the container, I will not be able to
identify which mount/volume I’m looking at/

Will I be able to do something like this:

GFile *file = g_mount_get_root( (GMount *) volume );
g_file_get_basename( file );

?

Thank you.

[pwithnall (Philip Withnall)]

Firstly, please give threads a descriptive title. Nobody except the couple of us who have been following along on the previous thread will know what “Follow-up questions” means. You’re narrowing your audience by doing so, and that means others won’t be able to find the questions and their answers in future.

---

@oneeyeman1

    for( volumes = volumelist; volumes != NULL; volumes = volumes->next )
        g_object_unref( volumes );
    g_list_free( volumelist );

I presume the code adobe is wrong as it throws an exception
on the g_object_unref().

You want to use g_object_unref (volumes->data) because the data in a linked list element (a GList) is stored in the data member.

This is a pretty simple use of a linked list. Please read the GList documentation to find out how linked lists work in GLib before starting to use them.

---

@oneeyeman1

I also tried this:

if( volumelist )
{
    g_list_foreach( volumes, g_object_unref, NULL );
    g_list_free( volumelist );
}

You should be passing volumelist rather than volumes to g_list_foreach(), and g_object_unref needs to be cast to GFunc to be passed to g_list_foreach(). Modern C requires explicit casts for function pointers, it won’t add an implicit cast for you.

---

@oneeyeman1

How do I uniquely identify the mounted volume?

That entirely depends on what use case you have, I can’t really answer that for you. Look through the methods of GVolume/GMount/GDrive and try them until you find something which you’re happy to use as an identifier.

ottomh methods like g_unix_mount_guess_name() are what’s used by Nautilus. If you want to know for sure, please look at the code of whatever app you think names things nicely, and copy from that.