About using custom icons in gtk +

For more information about how to use custom icons in gtk +-Linux general technology-Linux technology and application, see the following. About using custom icons in gtk +

Recently, I have been studying gtk + programming and want to use custom icons in the software's "menu items" and "tool items, A set of 48*48 png images are provided online and used in programs.
Gtk_image_menu_item_set_image (GTK_IMAGE_MENU_ITEM (file_new), gtk_image_new_from_file (DIR_ICO_FILE_NEW ));
Create a menu item with graphics, compile and run it, and find that the menu item is blank and there is no image.
I thought it was an image format problem. After converting a png Image to an xpm format using convert, the system compiled and ran it and found that there was still no image.
However, after using gtk_image_menu_item_new_from_stock () to compile and run the program, an image is displayed before the menu item ......
On google, there is a saying that the image Directory should use an absolute directory. After it is changed to an absolute directory, the problem persists.

This problem makes me very tangle. Most of the materials, such as devhelp, GTK + 2.0 tutorial, GTK study notes, and GTK + 2.0 programming examples, use gtk_image_menu_item_new_from_stock ()
How can I use a custom image ...... Hope you can help me!