There are a few issues with the provided code that could lead to the segmentation faults and memory leaks you’re encountering. I’ll break down the key points:

1. Iterators Initialization: You are passing uninitialized pointers (start and end) to gtk_text_buffer_get_start_iter and gtk_text_buffer_get_end_iter. These need to be valid GtkTextIter objects, not pointers to them. You should declare them as actual variables, not pointers.

2. Memory Management: You are not properly managing the memory of GListModel, GFile, and the strings returned by g_file_get_path. The memory needs to be released once you are done with it.

3. Avoid sprintf on path: You are using sprintf directly on the path pointer, which is already pointing to a string allocated by g_file_get_path. This is unnecessary and could lead to unexpected behavior. Instead, use a temporary buffer to append the newline character.

This is an updated version of your callback function:

static void
choseTargetFinish (GObject* source_object, GAsyncResult* res, gpointer data)
{
  GtkFileDialog *dialog = GTK_FILE_DIALOG (source_object);
  GListModel *files = gtk_file_dialog_open_multiple_finish(dialog, res, NULL);
  
  if (files != NULL)
  {
    // Declare actual GtkTextIter variables (not pointers)
    GtkTextIter start, end;
    
    // Clear the TextView content
    gtk_text_buffer_get_start_iter(targetPathBuffer, &start);
    gtk_text_buffer_get_end_iter(targetPathBuffer, &end);
    gtk_text_buffer_delete(targetPathBuffer, &start, &end);

    // Iterate over the selected files
    for (int i = 0; i < g_list_model_get_n_items(files); i++)
    {
      GFile *file = G_FILE(g_list_model_get_item(files, i));
      if (file != NULL)
      {
        // Get the file path
        char *path = g_file_get_path(file);
        
        if (path != NULL)
        {
          // Append newline and insert into TextView
          char *formatted_path = g_strdup_printf("%sn", path);
          gtk_text_buffer_get_end_iter(targetPathBuffer, &end);
          gtk_text_buffer_insert(targetPathBuffer, &end, formatted_path, -1);

          // Free the path and formatted_path
          g_free(path);
          g_free(formatted_path);
        }

        // Unref the GFile object
        g_object_unref(file);
      }
    }

    // Unref the GListModel after use
    g_object_unref(files);
  }
}

The main changes I made are:

1. GtkTextIter Variables: I changed GtkTextIter *start, *end to actual GtkTextIter start, end variables and passed their addresses to gtk_text_buffer_get_start_iter and gtk_text_buffer_get_end_iter.
2. Memory Management:
   • Added g_free() for the path and formatted_path strings.
   • Unreferenced each GFile object with g_object_unref(file) after processing it.
   • Unreferenced the GListModel after looping through the files with g_object_unref(files).
3. Formatted Path: Used g_strdup_printf to safely create a new string with the newline (n) and free it afterward.

This should resolve the segmentation faults, memory leaks, and the error messages you’re seeing.