Problem with GtkTextBuffer , Confusing Runtime Error. Need Help?

Question

I am using this code:

class editbook
{
  GtkWidget* _nbook;
  std::vector<GtkWidget*> _srcset; //and so on...

...........................................................................................

void editbook::add_page()
{
    GtkWidget* tmp = gtk_source_view_new();
    _srcset.push_back(tmp);
    gtk_notebook_append_page(GTK_NOTEBOOK(_nbook),tmp,gtk_label_new("untitled"));
}

...........................................................................................

void editbook::set_text(const std::string& text)
{
    int index = gtk_notebook_get_current_page(GTK_NOTEBOOK(_nbook));
    GtkTextBuffer* tbuffer = gtk_text_view_get_buffer(GTK_TEXT_VIEW(_srcset[index]));
    gtk_text_buffer_set_text(GTK_TEXT_BUFFER(tbuffer),text.c_str(),-1);
}

Compiles fine. But gives this weird runtime error:

Segementation Fault: return 139

I have traced down the problem to: gtk_text_view_get_buffer(GTK_TEXT_VIEW(_srcset[index]));

NOTE: I am using GtkSourceView instead of GtkTextView, but that may not be a problem because I am gettin the same error when I try GtkTextView.

NOTE: I am using Gtk 2x

NOTE: I am not sure whether to tag this question with C or C++. bec. Gtk+ is a C lib. But I am using C++. So I'll just tag both for now.

Could you post what is _srcset array? Btw why don't you use GtkMM ( gtkmm.org/en ) which is C++ wrapper over Gtk in case you want to write your code in C++? — another.anon.coward
– another.anon.coward, Commented Sep 22, 2011 at 10:28
@another.anon.coward std::vector<GtkWidget*> _srcset . Filled with GtkSourceViews (gtk_source_view_new()); As for GtkMM. Frankly I don't use it because I am an idiot... And because It doesn't compile on Ubuntu for some reason (glibmmconfig.h not found) — ApprenticeHacker
– ApprenticeHacker, Commented Sep 22, 2011 at 12:16
You're not showing enough information. Tell us where you define _srcset and why _srcset[index] must be a valid reference at the time of execution. — sehe
– sehe, Commented Sep 22, 2011 at 12:23
Hmmm ... Did you check if buffer returned for NULL & if they are valid objects? I mean what is the output for GTK_IS_TEXT_VIEW(_srcset[index]) & GTK_IS_TEXT_BUFFER(tbuffer)? Also, I would suggest you please use vector::at instead of operator[] just to be sure that you are not going out of the range. — another.anon.coward
– another.anon.coward, Commented Sep 22, 2011 at 12:35

another.anon.coward · Accepted Answer · 2011-09-23 12:40:22Z

The problem in your code could be that the child widget added to GtkNotebook through gtk_notebook_append_page is not visible, try showing the child widget through gtk_widget_show call. Something on these lines :

void editbook::add_page()
{
    GtkWidget* tmp = gtk_source_view_new();
    _srcset.push_back(tmp);
    gtk_widget_show(tmp); //Show the child widget to make it visible
    gtk_notebook_append_page(GTK_NOTEBOOK(_nbook),tmp,gtk_label_new("untitled"));
}

When you use gtk_notebook_get_current_page if none of the child widget are visible then it returns -1, which I think might be happening in your case & as index is -1 when you use operator[] which doesn't check for bounds the program crashes. I strongly suggest you use vector::at instead of using operator[] so that you get std::out_of_range exception during run time to indicate the problem. You could use:

void editbook::set_text(const std::string& text)
{
    int index = gtk_notebook_get_current_page(GTK_NOTEBOOK(_nbook));
    GtkTextBuffer* tbuffer = gtk_text_view_get_buffer(GTK_TEXT_VIEW(_srcset.at(index)));
    gtk_text_buffer_set_text(GTK_TEXT_BUFFER(tbuffer),text.c_str(),-1);
}

Hope this helps!

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