[boost] Re: uBLAS: problem with sparse_vector

From: Michael Stevens (support-1_at_[hidden])
Date: 2002-06-27 22:18:43

 >From: Marc Duflot <m.duflot_at_[hidden]>
 >To: boost_at_[hidden]
 >There is a bug in uBLAS that is illustrated with the following code:
 >    numerics::sparse_vector<double> v (3);
 >    v(1) = v(0) = 42;
 >    std::cout << v << std::endl;
 >}
 >
 >The output of the program is (with g++ 2.95.2 and g++ 3.0.4 on Linux)
 >[3](42,0,0)

 >The element v(1) is 0 instead of 42. The bug comes from the fact that 
v(1) is
 >evaluated before v(0) = 42. The bug is not present with the Intel 
compiler on
 >the same platform.

This bug seems to be GCC exclusive, it works fine with MSVC7. I can also 
confirm that GCC3.1 shows the same behaviour.
I suspect this to be a GCC bug and nothing to do with uBLAS. Looking at 
the execution path confirms this. All uBLAS 'v(x)' does is return a 
reference to a double

 >Note: there is the same problem with Loki::AssocVector.

This seems to confirm it is a compiler and not a library problem. Anyone 
out there know if GCC generaly has problems with returned references?

Michael