GTK+ Forums

szymzet · Joined: 29 May 2007 Posts: 3

I put comments in the code, any help is appreciated.

These are the parts I thought are the only necessary ones, if more needed just say so, I'll post them.

===========
signal connection
===========
g_signal_connect(G_OBJECT(main_window->calc_btn), "clicked",
G_CALLBACK(calculate_cb), main_window);

========
callback
==========
void calculate_cb(GtkWidget *widget, GdkEvent *event, MainWindow *main_window)
{
/*...*/
gchar *s;

/* I get Segmentation Fault here,
the window shows up, but when I press the button it terminates with this error */
s = gtk_editable_get_chars(GTK_EDITABLE(main_window->a_entry), 0, -1);
/*...*/
}

===========
MainWindow struct
============
typedef struct _MainWindow MainWindow;

struct _MainWindow
{
/* .. */
GtkWidget *a_entry;
/* ... */
};

deusvede · Posted: Tue May 29, 2007 7:42 pm Post subject:

Paste here the code where you allocate 'a_entry', please :).

szymzet · Joined: 29 May 2007 Posts: 3

======
main
======
int main(int argc, char *argv[])
{
MainWindow *main_window;

gtk_init(&argc, &argv);

main_window = main_window_create();

gtk_main();

return 0;
}

========
main_window_create
=========

MainWindow *main_window_create(void)
{
MainWindow *main_window;

main_window->window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_title(GTK_WINDOW(main_window->window), WINDOW_TITLE);

g_signal_connect(G_OBJECT(main_window->window), "delete_event",
G_CALLBACK(main_window_close_cb), NULL);
g_signal_connect(G_OBJECT(main_window->window), "destroy",
G_CALLBACK(destroy_cb), NULL);

/* ... */

main_window->calc_btn = gtk_button_new_with_label("calculate");
g_signal_connect(G_OBJECT(main_window->calc_btn), "clicked",
G_CALLBACK(calculate_cb), main_window);

main_window->a_entry = gtk_entry_new();

/* ... */

gtk_entry_set_max_length(GTK_ENTRY(main_window->a_entry), ENTRY_MAX_LEN);

/* ... showing widgets ...*/
return main_window;
}

openldev · Posted: Wed May 30, 2007 11:27 pm Post subject:

You must initialize the structure before you use it with g_slice_new() or g_malloc().

szymzet · Joined: 29 May 2007 Posts: 3

Well, could you say it a bit more clearly.

openldev · Posted: Sat Jun 02, 2007 3:03 pm Post subject:

MainWindow is a structure. When you call main_window_create(), you have a pointer called main_window. However, it points to nothing until you initialize it! So, when you try to reference main_window->window, it is trying to reference unallocated memory. Therefore, before you can use the structure, you must call:

Code: (Plaintext)
1	MainWindow *main_window = g_slice_new (MainWindow);

This will allocate memory for a new MainWindow structure and point main_window to it. If you get a seg fault, it usually means that you are trying to access memory that doesn't exist (unallocated), or you are trying to access memory that was already freed.