how to save a caneva

Hi,
 I use fltk (C++ graphical interface) to create an electronics design package. I created a list of objects and placed them on a window.

My problem is how to save the file, I think to create a list in memory for the objects placed on the sheet and store them in a file.

 I think (not sure of course) that xfig for example uses this procedure ?

Please whould you like give me how to do it or where can I find it a simple example or doc.

 thank you
 bela

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