How to find the header file and cflags about a specific function?

[丁少衡 <dshbusiness gmail com>]

I hope I post on the right list.
Now, I'm using gtk(or gnome related) libraries. Such as gconf and 
gsettings. But when I look up the documents, I find that the document 
does not tell me which header file should I include in my c source code.
For
 example, when I want to call gconf_client_get_default() or 
g_settings_new(), I wouldn't know which header file to include, if I did
 not search on the web.
Can anyone tell me how to find the information about header files in the
 documents? All I find in the documents says when I write a program using gtk+ function, I should include the gtk/gtk.h and use pkg-config --cflags --libs gtk+-3.0 as compile flags. But how about it when I use gsettings' or gconf's function or other function related to gnome?

Thanks!

dingshaoheng