[igraph] Graph attributes in R and C

[Matthew Walker]

Hi,

I have a problem, I suspect I know why, but if I'm right, I have no idea 
what to do!  All help would be gratefully received.

I have written a plugin system.  Graph measures are written in C/C++ and 
turned into plugins.  The plugins are loaded into a C++ program as 
specified by a configuration file.

My intention was that I could use R to test/debug each of the plugins.  
It all worked fine until I started to work with graph attributes.  
Hence, I think the graph attributes are my problem.

My R-based test case goes like this: I create a graph and add an 
attribute.  I load the plugin and pass the graph to it and ask the 
plugin to evaluate the graph.  When (in C) we get to reading the graph 
attribute, R dies with the error:
*** caught segfault ***
address (nil), cause 'unknown'

I suspect that I cannot use the C-based attribute handler for a graph 
that has been converted from R to C using R_SEXP_to_igraph().  Is this 
assumption correct?  I suspect this because of the considerable amount 
of attribute code in the file rinterface.c.

Thus, I guess my question is: Is there a correct way to do what I am 
trying to do?  Is there a way to convert an 
R-based-graph-with-attributes to a C-based-graph-with-attributes?  What 
would you do?

Thanks greatly in advance,

Matthew