Boost Graph Library: Exceptions

# `boost/graph/exception.hpp`

The BGL defines several exception classes for reporting errors from BGL algorithms. Many of the BGL algorithms place certain requirements on the input graph. If these requirements are not met then the algorithm can not successfully complete, and instead throws the appropriate exception.

### Synopsis

      struct bad_graph : public invalid_argument {
        bad_graph(const string& what_arg);
      };
      struct not_a_dag : public bad_graph {
        not_a_dag();
      };
      struct negative_edge : public bad_graph {
        negative_edge();
      };
      struct negative_cycle : public bad_graph {
        negative_cycle();
      };
      struct not_connected : public bad_graph {
        not_connected();
      };