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<H1>[Mono-list] Marshaling bug?
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<B>Jonathan Pryor
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<A HREF="mailto:jonpryor%40vt.edu"
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TITLE="[Mono-list] Marshaling bug?">jonpryor@vt.edu
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<I>Sat, 25 Oct 2003 13:23:43 -0400</I>
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<PRE>I don't think the problem is retrieving the value from g_list_nth_data.
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This is simple to check -- compare the value returned from
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g_list_nth_data against the value you put into the g_list.
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Or, just pass that value off to g_printf (DllImport it first):
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[DllImport(...)]
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static extern void g_printf (IntPtr format);
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The problem, as I had mentioned, appears to be in marshaling the return
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value (the unmanaged UTF-8 string) into managed memory (the char[]
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array), implying that "memmove" isn't being marshaled correctly.
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- Jon
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On Sat, 2003-10-25 at 13:08, <A HREF="mailto:pbaena@uol.com.ar">pbaena@uol.com.ar</A> wrote:
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><i> Thank you for all the suggestions. You're right. It seems that the problem is when retrieving from the g_list.
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</I>><i>
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</I>><i> The SWT API is very new so this is expected. The second approach I learned from Gtk#'s List wrapper. The intent of SWT is to be a thin layer on top of Gtk+ so I wouldn't dare to use Gtk#. All in all, Gtk# is very responsive, so I think it wouldn't hurt SWT to be a little higher level. Let's see how this evolves.
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</I>><i>
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</I>><i> Regards!!
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</I>><i>
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</I>><i> > Pardon me for saying this, but your SWT code is borked. Seriously.
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</I>><i> >
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</I>><i> > Why? Opaque pointer values should be expressed as a System.IntPtr, not
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</I>><i> > a System.Int32 ("int"). This is so that if you ever move to a platform
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</I>><i> > with a different sized pointer (say, 64-bit Opteron, or PowerPC 970, or
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</I>><i> > UltraSparc, or...), you won't kill all your pointer values.
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</I>><i> >
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</I>><i> > Furthermore, you've got arrays where you shouldn't have arrays.
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</I>><i> > Consider the prototype for g_utf8_to_utf16:
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</I>><i> >
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</I>><i> > gunichar* g_utf8_to_utf16 (const gchar *str,
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</I>><i> > glong len,
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</I>><i> > glong *items_read,
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</I>><i> > glong *items_written,
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</I>><i> > GError **error);
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</I>><i> >
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</I>><i> > Then, consider how C code would call it:
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</I>><i> >
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</I>><i> > int items_read, items_written;
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</I>><i> > const char* str = "this is my utf-8 string";
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</I>><i> > gunichar* result =
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</I>><i> > g_utf8_to_utf16 (str, strlen (str),
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</I>><i> > &items_read,
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</I>><i> > &items_written,
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</I>><i> > NULL /* ignore errors */);
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</I>><i> >
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</I>><i> > Assuming that we don't want to handle wrapping GError in C#, this would
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</I>><i> > be a better wrapper:
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</I>><i> >
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</I>><i> > [DllImport(...)]
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</I>><i> > static extern IntPtr g_utf8_to_utf16 (byte[] str, int len,
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</I>><i> > out int items_read, out int items_written,
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</I>><i> > IntPtr error /* pass IntPtr.Zero for this */);
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</I>><i> >
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</I>><i> > Notice that "items_read" and "items_written" are mapped to a "out"
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</I>><i> > parameter, instead of an array. This is more appropriate for this
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</I>><i> > function (and for any function similar to it -- items_read and
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</I>><i> > items_written aren't holding arrays, they're just an "out" pointer for
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</I>><i> > various data).
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</I>><i> >
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</I>><i> > To answer your last question: what's the advantage of this:
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</I>><i> >
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</I>><i> > string s = "Let's i18n, baby...do it hard!";
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</I>><i> > IntPtr unmanaged_memory = Marshal.StringToHGlobalAnsi (s);
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</I>><i> >
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</I>><i> > over the voluminous amounts of code you demonstrated before? Well, it's
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</I>><i> > shorter.
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</I>><i> >
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</I>><i> > But it's also seriously broken, at least from a
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</I>><i> > cross-platform/portability perspective. Here's why:
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</I>><i> >
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</I>><i> > - Not all platforms support "HGLOBAL". On Unix platforms, this is
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</I>><i> > likely to be normal g_malloc/g_free, but on Windows, this should
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</I>><i> > be using the GlobalAlloc and GlobalFree Win32 APIs. Which means
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</I>><i> > you have different functions to call on different platforms, which
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</I>><i> > will be a portability headache.
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</I>><i> >
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</I>><i> > - Even worse, StringToHGlobalAnsi creates an "Ansi" string. Ansi
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</I>><i> > IS NOT Utf-8. At least, you can't assume that it is, though it
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</I>><i> > *could* be. Ansi is, typically, the local code page, and if you've
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</I>><i> > been paying attention to the file-name handling thread on
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</I>><i> > mono-devel-list, you'd know that trying to mix the current code
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</I>><i> > page with Unicode handling is fraught with danger (and confusion,
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</I>><i> > and annoyance, and users with Pitchforks complaining about your
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</I>><i> > app not working right...).
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</I>><i> >
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</I>><i> > So, how do you do string-interop, portably, between Mono & GTK+? Well,
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</I>><i> > you could just use Gtk#, which will tackle this issue (eventually; it
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</I>><i> > appears to use Marshal.StringToHGlobalAnsi in some places, so it's
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</I>><i> > likely assuming that, under Mono, Ansi == UTF-8). This is certainly the
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</I>><i> > easiest way to go, unless you're dead set on providing *another* GTK+
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</I>><i> > wrapper. (Of course, this places a Gtk# dependency on SWT, which may be
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</I>><i> > undesirable.)
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</I>><i> >
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</I>><i> > If you do it on your own, you're pretty much stuck doing what you're
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</I>><i> > doing in your first example.
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</I>><i> >
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</I>><i> > As for why it doesn't work, it could be a regression. On my system, it
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</I>><i> > appears to be correctly converting the .NET UTF-16 input string "str"
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</I>><i> > into a UTF-8 string -- I'm able to pass "data" to g_printf and see
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</I>><i> > unmanaged representation.
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</I>><i> >
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</I>><i> > It's the return trip -- converting the UTF-8 unmanaged memory and
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</I>><i> > copying it into the CLI char[] array, that appears to be the problem.
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</I>><i> > I'll need to write a small test case, and if this is a new marshalling
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</I>><i> > bug, I'll file it in bugzilla.
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</I>><i> >
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</I>><i> > Thanks,
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</I>><i> > - Jon
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</I>><i> >
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</I>><i> > On Sat, 2003-10-25 at 09:52, <A HREF="mailto:pbaena@uol.com.ar">pbaena@uol.com.ar</A> wrote:
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</I>><i> > > I reported a bug (#50116) about this problem of mine (of SWT really), and I wanted to get help from the experts to see if the API can be improved.
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</I>><i> > >
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</I>><i> > > SWT works this way to append and retrieve from a g_list:
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</I>><i> > >
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</I>><i> > > --------------------------------CODE-------------------------
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</I>><i> > > using System;
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</I>><i> > > using System.Runtime.InteropServices;
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</I>><i> > >
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</I>><i> > > class testbug {
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</I>><i> > >
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</I>><i> > > public const string GLIB_LIBRARY = "glib-2.0";
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</I>><i> > > public const string STRLEN_LIBRARY = "pango-1.0";
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</I>><i> > > public const string MEMMOVE_LIBRARY = "gtk-x11-2.0";
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</I>><i> > >
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int g_utf16_to_utf8(char[] str, int len, int[]
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</I>><i> > > items_read, int[] items_written, int[] error);
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int g_utf8_to_utf16(byte[] str, int len, int[]
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</I>><i> > > items_read, int[] items_written, int[] error);
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</I>><i> > >
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</I>><i> > > [DllImport(STRLEN_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int strlen(int str);
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</I>><i> > >
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</I>><i> > > [DllImport(MEMMOVE_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void memmove(int dest, int[] src, int size);
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</I>><i> > > [DllImport(MEMMOVE_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void memmove(int dest, byte[] src, int size);
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</I>><i> > > [DllImport(MEMMOVE_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void memmove(int[] dest, byte[] src, int size);
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</I>><i> > > [DllImport(MEMMOVE_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void memmove(byte[] dest, int src, int size);
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</I>><i> > > [DllImport(MEMMOVE_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void memmove(char[] dest, int src, int size);
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</I>><i> > > [DllImport(MEMMOVE_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void memmove(int[] dest, int src, int size);
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</I>><i> > >
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern void g_free(int mem);
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int g_malloc(int size);
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</I>><i> > >
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int g_list_append(int list, int data);
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int g_list_nth_data(int list, int n);
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</I>><i> > >
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</I>><i> > >
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</I>><i> > > public static void Main ()
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</I>><i> > > {
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</I>><i> > > string str = "Let's i18n, baby...do it hard!";
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</I>><i> > > int glist = 0;
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</I>><i> > > bool terminate = true;
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</I>><i> > > char [] strchar = str.ToCharArray();
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</I>><i> > >
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</I>><i> > > int [] items_read = new int [1], items_written = new int [1];
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</I>><i> > > int ptr = g_utf16_to_utf8 (strchar, str.Length, items_read,
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</I>><i> > > items_written, null);
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</I>><i> > >
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</I>><i> > > int written = items_written [0];
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</I>><i> > > //TEMPORARY CODE - convertion stops at the first NULL
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</I>><i> > > if (items_read [0] != strchar.Length) written++;
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</I>><i> > > byte [] buffer = new byte [written + (terminate ? 1 : 0)];
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</I>><i> > > memmove (buffer, ptr, written);
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</I>><i> > > g_free (ptr);
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</I>><i> > >
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</I>><i> > > int data = g_malloc (buffer.Length);
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</I>><i> > > memmove (data, buffer, buffer.Length);
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</I>><i> > > glist = g_list_append (glist, data);
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</I>><i> > >
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</I>><i> > > data = g_list_nth_data (glist, 0);
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</I>><i> > > int length = strlen (data);
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</I>><i> > > byte [] buffer1 = new byte [length];
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</I>><i> > > memmove (buffer1, data, length);
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</I>><i> > >
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</I>><i> > > ptr = g_utf8_to_utf16 (buffer1, buffer1.Length, null,
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</I>><i> > > items_written, null);
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</I>><i> > >
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</I>><i> > > length = items_written [0];
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</I>><i> > > char [] chars = new char [length];
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</I>><i> > > memmove (chars, ptr, length * 2);
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</I>><i> > >
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</I>><i> > > Console.WriteLine (chars);
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</I>><i> > >
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</I>><i> > > g_free (ptr);
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</I>><i> > > }
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</I>><i> > >
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</I>><i> > > }
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</I>><i> > > ------------------------------------------------------------------
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</I>><i> > >
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</I>><i> > > That worked till mono 0.28, but doesn't work with current mono from CVS. Now I was testing things and found that this other approach to the problem works:
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</I>><i> > >
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</I>><i> > > ------------------------------CODE--------------------------------
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</I>><i> > > using System;
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</I>><i> > > using System.Runtime.InteropServices;
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</I>><i> > >
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</I>><i> > > class testbug {
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</I>><i> > >
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</I>><i> > > public const string GLIB_LIBRARY = "glib-2.0";
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</I>><i> > >
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern int g_list_append(int list, IntPtr data);
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</I>><i> > > [DllImport(GLIB_LIBRARY, CharSet = CharSet.Unicode)]
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</I>><i> > > public static extern string g_list_nth_data(int list, int n);
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</I>><i> > >
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</I>><i> > > public static void Main ()
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</I>><i> > > {
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</I>><i> > > string str = "Let's i18n, baby...do it hard!";
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</I>><i> > > int glist = 0;
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</I>><i> > >
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</I>><i> > > glist = g_list_append (glist, Marshal.StringToHGlobalAnsi (str));
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</I>><i> > > string data2 = g_list_nth_data (glist, 0);
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</I>><i> > > Console.WriteLine (data2);
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</I>><i> > >
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</I>><i> > > return;
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</I>><i> > > }
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</I>><i> > >
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</I>><i> > > }
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</I>><i> > > ----------------------------------------------------------------
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</I>><i> > >
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</I>><i> > > Now I was wondering what are the advantages of the latest approach in contrast with SWT's. Can you give me some advice?
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</I>><i> > >
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</I>><i> > > Thank you very much!
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</I>><i> > > Pablo
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</I>><i> > > _______________________________________________
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</I>><i> > > Mono-list maillist - <A HREF="mailto:Mono-list@lists.ximian.com">Mono-list@lists.ximian.com</A>
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</I>><i> > > <A HREF="http://lists.ximian.com/mailman/listinfo/mono-list">http://lists.ximian.com/mailman/listinfo/mono-list</A>
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</I>><i> >
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</I>><i> > _______________________________________________
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</I>><i> > Mono-list maillist - <A HREF="mailto:Mono-list@lists.ximian.com">Mono-list@lists.ximian.com</A>
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</I>><i> > <A HREF="http://lists.ximian.com/mailman/listinfo/mono-list">http://lists.ximian.com/mailman/listinfo/mono-list</A>
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</I>><i> _______________________________________________
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</I>><i> Mono-list maillist - <A HREF="mailto:Mono-list@lists.ximian.com">Mono-list@lists.ximian.com</A>
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</I>><i> <A HREF="http://lists.ximian.com/mailman/listinfo/mono-list">http://lists.ximian.com/mailman/listinfo/mono-list</A>
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</I>
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</PRE>
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