Load and use a Glade layout in GTK2/C

Question

I was trying to load a Glade layout into a GTK2 C code.

It consists of a window in which there is a VBox with 2 elements: a label and a button. I want to associate a signal to the button to close the application.

If I make all of this by using only C code it works fine, but when I load a layout I receive the following runtime error (the application starts but the button doesn't work):

(main:2581): GLib-GObject-WARNING **: 21:38:46.789: invalid (NULL) pointer instance (main:2581): GLib-GObject-CRITICAL **: 21:38:46.790: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

Here the code I used, mylayout.glade is a file in my project folder:

#include <gtk/gtk.h> void end_program (GtkWidget * wid, gpointer ptr) { gtk_main_quit(); return; } int main (int argc, char * argv[]) { GError * error = NULL; gtk_init(&argc, &argv); GtkBuilder * builder = gtk_builder_new(); if (0 == gtk_builder_add_from_file(builder, "mylayout.glade", &error)) { g_printerr("Error loading file: %s\n", error->message); g_clear_error(&error); return 1; } GtkWidget * win = (GtkWidget *) gtk_builder_get_object(builder, "window1"); GtkWidget * btn = (GtkWidget *) gtk_builder_get_object(builder, "button1"); g_signal_connect(btn, "clicked", G_CALLBACK(end_program), NULL); gtk_widget_show_all(win); gtk_main(); return 0; }

The only thing I noticed is that if I remove the g_signal_connect() line the error disappear.

Any help is really appreciated.

You don't check your return values for NULL. If that g_signal_connect call causes these messages, then btn is NULL. — Gerhardh
– Gerhardh, Commented May 6, 2022 at 19:57
Solved, GTK2 has errors that are different from the classic gcc compiler and I didn't know what was the error. Thank you @Gerhardh — Crazy circuit
– Crazy circuit, Commented May 8, 2022 at 19:28
I have no idea what you mean by "has errors that are different from the classic GCC compiler". To see the errors, you must check return values. A compiler can only report syntax errors. The vast majority of errors are runtime errors your compiler cannot tell you. — Gerhardh
– Gerhardh, Commented May 10, 2022 at 8:19

NoDakker · Accepted Answer · 2022-05-06 21:19:01Z

You might want to check the name you gave your button widget in the glade file. The only way I could replicate your error was when the name of the button widget defined in the glade file was something different from "button1" as referenced in the program statement:

GtkWidget * btn = (GtkWidget *) gtk_builder_get_object(builder, "button1");

When the glade file had a different name for the button (e.g. "button" or "btn"), then I received the identical warning and critical error message as you noted.

Regards.

Yep, it's right! It is the first time I get these errors and now I know what's their origin. I can confirm that the real name of the button, in my case, was "button2".

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