GTK get multiple range value segmentation error - c

Question

So, I'm trying to create an rgb selector with gtk in C.
I follow the documentation to learn how to put in place a glade project and use it with gtk, so I made an UI in glade, but I have some trouble with the GTK part. I need to have access to multiple slider in the change-value signal because I want to get their value to print them, so I have created a struct to stock them, and I send this struct in the signal. But my problem is when I try to get the value of the range which his stock in the struct I have a segmentation error and I don't know why. I tried without the struct and I can correctly get the slider value, but it didn't work with the struct. How can I fix it?
Ask me if you need the glade file too.
//Compil : gcc -rdynamic -o ColorPicker colorPicker.c `pkg-config --cflags --libs gtk+-3.0`
#include <gtk/gtk.h>
#include <glib/gstdio.h>
#include <gdk/gdk.h>
typedef struct
{
GObject *redSlider;
GObject *blueSlider;
GObject *greenSlider;
GObject *label;
}Data;
static void changeLabel (GtkWidget *range, Data *data)
{
gdouble red = gtk_range_get_value(GTK_RANGE(data->redSlider));
g_print("%.0lf\n",red);
//g_print("R : %d, G : %d, B : %d",red,green,blue);
}
static void activate(GtkApplication *app, gpointer user_data)
{
Data *data;
data = malloc(sizeof(*data));
GtkBuilder *builder = gtk_builder_new();
gtk_builder_add_from_file(builder, "colorPicker.glade",NULL);
GObject *window = gtk_builder_get_object (builder, "window");
gtk_window_set_application (GTK_WINDOW (window), app);
data->redSlider = gtk_builder_get_object (builder, "redSlider");
g_signal_connect (data->redSlider, "change-value", G_CALLBACK (changeLabel), (gpointer) data);
data->blueSlider = gtk_builder_get_object (builder, "blueSlider");
g_signal_connect (data->blueSlider, "change-value", G_CALLBACK (changeLabel), (gpointer) data);
data->greenSlider = gtk_builder_get_object (builder, "greenSlider");
g_signal_connect (data->greenSlider, "change-value", G_CALLBACK (changeLabel), (gpointer) data);
data->label = gtk_builder_get_object (builder, "cpChooseLabel");
/*GObject *colorBtn = gtk_builder_get_object (builder, "colorBtn");
g_signal_connect (colorBtn, "clicked", G_CALLBACK (getColor), (gpointer) data);*/
gtk_widget_show (GTK_WIDGET (window));
/* We do not need the builder any more */
g_object_unref (builder);
free(data);
}
int main(int argc, char **argv)
{
#ifdef GTK_SRCDIR
g_chdir(GTK_SRCDIR);
#endif
GtkApplication *app = gtk_application_new("com.github.XXXXXX.rgbSelector", G_APPLICATION_FLAGS_NONE);
g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
int status = g_application_run(G_APPLICATION(app), argc, argv);
g_object_unref(app);
return status;
}

Answer 1

You end the structure's lifetime by freeing it at the end of activate. When the callback changeLabel is invoked at some time later, it tries to access the no longer existing structure. You could just drop the free(data); if you don't care that the space occupied by the four pointers can't be freed then; another possibility is to simply use a static structure and pass its address.