Your first mistake might be to ask this question in a gtk forum and not in a linux developer forum. Nevertheless the easiest solution might be to add your user to the group which owns the file.
Many thanks for your answer asdfgh2091, yes you right, the question may be differs slightly GTK, but the program I'm writing in GTK, and I want to display in a GtkWindow list of all the PC's serial ports. The program works fine, and I get a complete list of devices, with I/O address and IRQ values, but only works in root.
I will question another way, how do in GTK programs to display a dialog box and ask for the root password?
Show this easy, but once you have the password, how it is used from the program?
For example, programs such as YaST, Apptitude and other...
Or in others words, how is possible get root privileges programming in GTK?