Add C++ ForwardGraph::demes_graph to get a string representation of t…

…he resolved graph (#1297)

cpptests/test_forward_demes_graph.cc

@@ -24,6 +24,7 @@ BOOST_FIXTURE_TEST_CASE(test_zero_length_single_deme_model, SingleDemeModel)
             pop.generation += 1;
         }
     BOOST_REQUIRE_EQUAL(pop.generation, 0);
+    auto graph = g.demes_graph();
 }
 
 BOOST_FIXTURE_TEST_CASE(single_deme_model_with_burn_in, SingleDemeModel)

lib/core/demes/forward_graph.hpp

@@ -57,5 +57,6 @@ namespace fwdpy11_core
         // gets a fn to handle this
         std::uint32_t sum_deme_sizes_at_time_zero();
         std::vector<std::uint32_t> parental_deme_sizes_at_time_zero() const;
+        std::string demes_graph() const;
     };
 }

lib/demes/forward_graph.cc

@@ -312,4 +312,19 @@ namespace fwdpy11_core
 
         return rv;
     }
+
+    std::string
+    ForwardDemesGraph::demes_graph() const
+    {
+        std::int32_t status;
+        auto temp = demes_forward_graph_get_demes_graph(&status, pimpl->graph.get());
+        if (status != 0)
+            {
+                free(const_cast<char *>(temp));
+            }
+        pimpl->handle_error_code(status);
+        auto rv = std::string(temp);
+        free(const_cast<char *>(temp));
+        return rv;
+    }
 }

rust/fp11rust/src/demes_capi_bridge.rs

@@ -148,6 +148,14 @@ pub unsafe extern "C" fn demes_forward_graph_model_end_time(
     forward_graph_model_end_time(status, graph)
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn demes_forward_graph_get_demes_graph(
+    status: *mut i32,
+    graph: *const OpaqueForwardGraph,
+) -> *const c_char {
+    forward_graph_get_demes_graph(graph, status)
+}
+
 // Below are functions defined only for fwdpy11.
 // These make use of demes_forward_capi.
 
@@ -175,6 +183,6 @@ pub unsafe extern "C" fn demes_forward_graph_sum_sizes_at_time_zero(
         return f64::NAN;
     }
     let size_slice = std::slice::from_raw_parts(ptr, num_demes as usize);
-    assert_eq!(size_slice.len(), num_demes as usize); 
+    assert_eq!(size_slice.len(), num_demes as usize);
     size_slice.iter().sum()
 }