Re: How to store Gdk::Pixbuf pixels into std::string objects

[Yann LEYDIER <yann leydier info>]

According to this : 
http://www.cplusplus.com/reference/string/basic_string/basic_string/

"If the resulting string length would exceed the max_size, a 
length_error exception is thrown."

Your image is to big to fit in a std::string.

On 23/02/2015 23:05, Glus Xof wrote:
> 2015-02-23 22:21 GMT+01:00 Markus Kolb <markus kolb+gtkmm tower-net de
> <mailto:markus kolb+gtkmm tower-net de>>:
>
>     Am 2015-02-23 21:40, schrieb Glus Xof:
>
>         Hi guys,
>
>         Before anything, I admit that probably my question is not an
>         specifically
>         Gtkmm question... but nevertheless I think you may know how
>         Gdk::Pixbuf is
>         done...
>
>         Having the following,
>
>         Glib::RefPtr<Gdk::Pixbuf> ref_orig = Gdk::Pixbuf::create_from_file
>         ("./file.png");
>
>         I'm trying to temporary store (because I need so) the image data
>         into a
>         std::string object. It seems that get_pixels() could solve the
>         problem,
>         getting a pointer of type guint8.
>
>
>     Seems that gdkmm is not up-to-date here.
>     gdk uses a guchar*. But this shouldn't be a problem.
>
>
>         So, I wrote as follows,
>
>         std::string image_pixels (reinterpret_cast<const char
>         *>(ref_orig->get_pixels()), ref_orig->get_rowstride());
>
>
>     I think this does not what you expect.
>
>     
> https://developer.gnome.org/__gdk-pixbuf/stable/gdk-pixbuf-__The-GdkPixbuf-Structure.html#__gdk-pixbuf-get-rowstride
>     
> <https://developer.gnome.org/gdk-pixbuf/stable/gdk-pixbuf-The-GdkPixbuf-Structure.html#gdk-pixbuf-get-rowstride>
>
>     See also the part below the description headline.
>
>     Maybe you should use gsize Gdk::Pixbuf::get_byte_length()
>     because
>     
> https://developer.gnome.org/__gdk-pixbuf/stable/gdk-pixbuf-__The-GdkPixbuf-Structure.html#__gdk-pixbuf-get-pixels-with-__length
>     
> <https://developer.gnome.org/gdk-pixbuf/stable/gdk-pixbuf-The-GdkPixbuf-Structure.html#gdk-pixbuf-get-pixels-with-length>
>     is missing.
>
>     I hope it will help you.
>
>     But think about the std::string. Big ? ;-)
>
>
> According to Yann & Markus' comments, I remake my code as follows,
>
> Glib::RefPtr<Gdk::Pixbuf> ref_orig = Gdk::Pixbuf::create_from_file
> ("./file.png");
>
> // Glib::ustring::c_str() or data() allows me to get an std::string
> object...
>
> Glib::ustring image_pixels (
>        reinterpret_cast<const char *>(ref_orig->get_pixels()),
>        ref_orig->get_byte_length());
>
> Glib::RefPtr<Gdk::Pixbuf> ref_dest =
>        Gdk::Pixbuf::create_from_data (
>           reinterpret_cast<const guint8*>(image_pixels.data()),
> Gdk::COLORSPACE_RGB,
>           ref_orig->get_has_alpha(), ref_orig->get_bits_per_sample(),
>           ref_orig->get_width(), ref_orig->get_height(),
> ref_orig->get_rowstride());
>
> But, at runtime I get a lenght error exception,
>
> terminate called after throwing an instance of 'std::length_error'
>    what():  basic_string::_S_create
>
> Could help ?
>
> Glus
>
>
>
>
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