Is anyone actually using gstreamermm?

[Nicolas Dufresne]

Le jeu. 12 mars 2020 07 h 15, Carlos Rafael Giani <crg7475 at mailbox.org> a
écrit :

>
> On 11.03.20 21:57, Marcin Kolny wrote:
> > In terms of plugins; it's actually possible to write them fully in
> > C++. Unfortunately I never managed to write any example, but there's a
> > few tests which you can treat as examples [1].
>
>
> I've done that in the past. This is largely straightforward, but there
> are a few gotchas:
>
>
> 1. Any C++ objects in the element and element class structures must be
> initialized with placement-new (don't forget to include the <new> header
> for this!) and have their destructors explicitely called. That's because
> the structures are allocated with C allocators, which know nothing about
> constructors and destructors. Example:
>
> struct MyGstElement
> {
>    GstElement parent;
>
>    MyCppObject cpp_object;
> };
>
> ....
>
> void my_gst_element_init(MyGstElement *self)
> {
>    new (&self->cpp_object) MyCppObject(<constructor arguments>);
> }
>
> void my_gst_element_finalize(GObject *object)
> {
>    ...
>    self->cpp_object.~MyCppObject();
>    ...
> }
>
> Since this can get annoying quickly if you have many C++ objects in your
> element, I recommend creating one struct with all C++ objects inside,
> and then call that struct's constructor and destructor in _init() and
> _finalize().
>
>
> 2. Surround GST_PLUGIN_DEFINE() with extern "C" { }. Otherwise, name
> mangling may mess up the symbols that the plugin loader looks for.
>

This is already handled by that macro.


>
> 3. Sometimes, people like to write internal structs and call the struct
> instances something like "private". But "private" is a C++ keyword!
>
>
> 4. I recommend using std::string as often as you can instead of C
> strings, since the former are _so_ much nicer and easier to use. But
> when combining them with GObject properties, GstStructures etc. you must
> always remember to convert from/to C strings. Since the type is erased
> at compile time, nothing will warn you or produce an error, you can
> easily get a crash instead.
>
>
> 5. C++ is more strict about implicit casts. In particular, in GParam
> functions like g_param_spec_uint(), the flags parameter is often set to
> a bitwise OR combination of enums, like G_PARAM_READWRITE |
> G_PARAM_STATIC_STRINGS . In C, this is implicitely cast to GParamFlags.
> In C++, you get a compiler error, so you must explicitely cast this,
> like so: GParamFlags(G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS)
>
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>
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