What functions should I use in GTK to open a file(such as text or image ) with default application?

["haitao_yang foxitsoftware com" <haitao_yang foxitsoftware com>]

Hi,
	I have two problems: 1)How can I open a file(such as text or image )
with default application? 2)How can I set my program as default
application to open specific type of file? I wonder if GTK provide some
function to carry out such operations? And what preference materials can
I look for? (something like windows function ShellExecuteA(NULL,
"open",.....))
	Thanks advance!
-- 
Sincerely,
Alfred Young