id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
3151,Patch to graph library iterator handling,tkeitt@…,Douglas Gregor,"I have developed some graph classes that generate edge lists on-the-fly (queried from a database). This means that my iterator ranges are not stable across calls to edges or out_edges. I have therefor altered the graph library to avoid comparing iterator across calls to vertices, edges, out_edges, etc.

A common example occurs in a number of locations in the graph library:

edge_iterator ei;
for ( ei = out_edges(v, g).first, ei != out_edges(v, g).second, ++ei)
{
  ...
}

Notice that ei is compared to subsequent calls to out_edges (this breaks my code).

A synonymous change is to re-write this as:

edge_iterator ei, e_end;
for (tie(ei, e_end) = out_edges(v, g); ei != e_end; ++ei)
{
  ...
}

The behavior of the code is not changed and is perhaps a bit easier to read. This version will not break my code because ei is only compared to e_end.

I have tried to remove all occurrences of comparing iterators to (vertices|edges|out_edges|...)(...).second and replace them with code that only compares iterators from the same call to (vertices|edges|out_edges|...).

I also added a file called pair_util.hpp which defines templates that make it easy to test whether members of a pair are equal or not equal.

I am attaching a patch. I have run the graph regression tests and all pass except one that does not pass before the patch.
",Patches,closed,Boost 1.40.0,graph,Boost Development Trunk,Problem,fixed,"graph, iterator",