C and GTK g_signal_connect Passing parameters - c

Question

Cannot get g_signal_connect to pass parameters correctly. Its probably because I do not understand the "c_handler" or "data" parameters. The code is here:
#include <gtk/gtk.h>
// Function prototypes
void my_file_saveas();
// Function
void my_file_saveas(GtkTextBuffer *buf)
{
// Get the start and end bounds of the buffer
GtkTextIter start, end;
gtk_text_buffer_get_bounds (buf, &start, &end);
}
int main(int argc, char *argv[])
{
GtkWidget *menubar;
GtkWidget *fileMenu;
GtkWidget *fileMh;
GtkWidget *saveasMi;
GtkWidget *view;
GtkTextBuffer *buffer;
GtkWidget *scroll_window;
GtkWidget *vbox;
GtkWidget *window;
// Call this function first
gtk_init(&argc, &argv);
// Create widgets
menubar = gtk_menu_bar_new();
fileMenu = gtk_menu_new();
fileMh = gtk_menu_item_new_with_label("File");
saveasMi = gtk_menu_item_new_with_label("Save As");
view = gtk_text_view_new();
buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (view));
// Set out the menubar
gtk_menu_shell_append(GTK_MENU_SHELL(fileMenu), saveasMi);
gtk_menu_item_set_submenu(GTK_MENU_ITEM(fileMh), fileMenu);
gtk_menu_shell_append(GTK_MENU_SHELL(menubar), fileMh);
// Create a scroll window and add the view to it
scroll_window = gtk_scrolled_window_new (NULL, NULL);
gtk_container_add(GTK_CONTAINER(scroll_window), view);
// Create a vertical box and add the menubar and scroll_window
vbox = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
gtk_box_pack_start(GTK_BOX(vbox), menubar, FALSE, FALSE, 0);
gtk_box_pack_start(GTK_BOX(vbox), scroll_window, TRUE, TRUE, 0);
// Setup top level window
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 640, 480);
// Put the box in the top level window
gtk_container_add(GTK_CONTAINER(window), vbox);
// Events
g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL);
g_signal_connect(G_OBJECT(saveasMi), "activate", G_CALLBACK(my_file_saveas), buffer);
// Display the window
gtk_widget_show_all(window);
// Runs main
gtk_main();
return 0;
}
It compiles OK. But the output when I run it is here:
graeme#graeme-HP-xw4300-Workstation ~/c/test $ ./ed10
(ed10:2974): Gtk-CRITICAL **: gtk_text_buffer_get_bounds: assertion 'GTK_IS_TEXT_BUFFER (buffer)' failed

Answer 1

Your error is self-explanatory (kind of):
(debugsig:26923): Gtk-CRITICAL **: gtk_text_buffer_get_bounds:
assertion 'GTK_IS_TEXT_BUFFER (buffer)' failed
Looking at your code -- you do not declare an independent GTK_TEXT_BUFFER (e.g. GtkTextBuffer *). gtk_text_view_new will provide a default buffer, but you can alternatively use gtk_text_view_new_with_buffer (buffer) if you independently declare a buffer with, e.g. gtk_text_buffer_new (NULL); (you will get a default buffer with either gtk_text_view_new or gtk_text_view_new_with_buffer (NULL);). Your choice..., what you have will work.
Your real problem is your callback function prototype is wrong, it should contain your menuitem (that is the real issue, it is taking your buffer as a GtkMenuItem causing the error 'GTK_IS_TEXT_BUFFER (buffer)' failed), e.g.
void my_file_saveas (GtkMenuItem *menuitem, gpointer data)
{
// Get the start and end bounds of the buffer
GtkTextBuffer *buf = GTK_TEXT_BUFFER (data);
GtkTextIter start, end;
gtk_text_buffer_get_bounds (buf, &start, &end);
/* print the number of lines to stdout */
g_print ("Buffer has %d lines.\n", gtk_text_iter_get_line (&end) -
gtk_text_iter_get_line (&start) + 1);
if (menuitem) {} /* stub to suppress warning of unused menuitem */
}
Candidly, I cannot believe it let you compile without error (or warning), but it did, I compiled with:
gcc -Wall -Wextra -pedantic -finline-functions -std=gnu11 ...
and it let me compile with the incorrect prototype too -- wrapped me around the axle for a bit :)
Here is a working example of your code:
#include <gtk/gtk.h>
// Function
void my_file_saveas (GtkMenuItem *menuitem, gpointer data)
{
// Get the start and end bounds of the buffer
GtkTextBuffer *buf = GTK_TEXT_BUFFER (data);
GtkTextIter start, end;
gtk_text_buffer_get_bounds (buf, &start, &end);
g_print ("Buffer has %d lines.\n", gtk_text_iter_get_line (&end) -
gtk_text_iter_get_line (&start) + 1);
if (menuitem) {} /* stub to suppress warning of unused menuitem */
}
int main(int argc, char *argv[])
{
GtkWidget *menubar;
GtkWidget *fileMenu;
GtkWidget *fileMh;
GtkWidget *saveasMi;
GtkWidget *view;
GtkTextBuffer *buffer = NULL;
GtkWidget *scroll_window;
GtkWidget *vbox;
GtkWidget *window;
// Call this function first
gtk_init(&argc, &argv);
// Create widgets
menubar = gtk_menu_bar_new();
fileMenu = gtk_menu_new();
fileMh = gtk_menu_item_new_with_label("File");
saveasMi = gtk_menu_item_new_with_label("Save As");
/** example declaring independent buffer
*
* buffer = gtk_text_buffer_new (NULL);
* view = gtk_text_view_new_with_buffer(buffer);
*/
view = gtk_text_view_new();
buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (view));
if (!view || !buffer) {
g_print ("error - no view or buf.\n");
return 1;
}
// Set out the menubar
gtk_menu_shell_append(GTK_MENU_SHELL(fileMenu), saveasMi);
gtk_menu_item_set_submenu(GTK_MENU_ITEM(fileMh), fileMenu);
gtk_menu_shell_append(GTK_MENU_SHELL(menubar), fileMh);
// Create a scroll window and add the view to it
scroll_window = gtk_scrolled_window_new (NULL, NULL);
gtk_container_add(GTK_CONTAINER(scroll_window), view);
// Create a vertical box and add the menubar and scroll_window
vbox = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
gtk_box_pack_start(GTK_BOX(vbox), menubar, FALSE, FALSE, 0);
gtk_box_pack_start(GTK_BOX(vbox), scroll_window, TRUE, TRUE, 0);
// Setup top level window
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 640, 480);
// Put the box in the top level window
gtk_container_add(GTK_CONTAINER(window), vbox);
// Events
g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL);
g_signal_connect(G_OBJECT(saveasMi), "activate", G_CALLBACK(my_file_saveas),
buffer);
// Display the window
gtk_widget_show_all(window);
// Runs main
gtk_main();
return 0;
}
If you want to look at a bit of a larger example (GTK+2, but 100% applicable here), take a look at https://github.com/drankinatty/gtkwrite. (The textview and buffer declarations are in gtk_windef.c)