add c_api.StringPiece to avoid crash for unmanaged memory.

src/TensorFlowNET.Core/Operations/Operation.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using System.Text;
 
 namespace Tensorflow
@@ -14,16 +15,16 @@ namespace Tensorflow
 
         private Status status = new Status();
 
-        public string name { get; }
-        public string optype { get; }
-        public string device { get; }
-        public int NumOutputs { get; }
-        public TF_DataType OutputType { get; }
-        public int OutputListLength { get; }
-        public int NumInputs { get; }
-        public int NumConsumers { get; }
-        public int NumControlInputs { get; }
-        public int NumControlOutputs { get; }
+        public string name => c_api.StringPiece(c_api.TF_OperationName(_handle));
+        public string optype => c_api.StringPiece(c_api.TF_OperationOpType(_handle));
+        public string device => c_api.StringPiece(c_api.TF_OperationDevice(_handle));
+        public int NumOutputs => c_api.TF_OperationNumOutputs(_handle);
+        public TF_DataType OutputType => c_api.TF_OperationOutputType(new TF_Output(_handle, 0));
+        public int OutputListLength => c_api.TF_OperationOutputListLength(_handle, "output", status);
+        public int NumInputs => c_api.TF_OperationNumInputs(_handle);
+        public int NumConsumers => c_api.TF_OperationOutputNumConsumers(new TF_Output(_handle, 0));
+        public int NumControlInputs => c_api.TF_OperationNumControlInputs(_handle);
+        public int NumControlOutputs => c_api.TF_OperationNumControlOutputs(_handle);
 
         private Tensor[] _outputs;
         public Tensor[] outputs => _outputs;
@@ -35,17 +36,6 @@ namespace Tensorflow
                 return;
 
             _handle = handle;
-
-            name = c_api.TF_OperationName(_handle);
-            optype = c_api.TF_OperationOpType(_handle);
-            device = "";// c_api.TF_OperationDevice(_handle);
-            NumOutputs = c_api.TF_OperationNumOutputs(_handle);
-            OutputType = c_api.TF_OperationOutputType(new TF_Output(_handle, 0));
-            OutputListLength = c_api.TF_OperationOutputListLength(_handle, "output", status);
-            NumInputs = c_api.TF_OperationNumInputs(_handle);
-            NumConsumers = c_api.TF_OperationOutputNumConsumers(new TF_Output(_handle, 0));
-            NumControlInputs = c_api.TF_OperationNumControlInputs(_handle);
-            NumControlOutputs = c_api.TF_OperationNumControlOutputs(_handle);
         }
 
         public Operation(Graph g, string opType, string oper_name)
@@ -62,8 +52,8 @@ namespace Tensorflow
             Graph = g;
 
             _id_value = Graph._next_id();
+
             _handle = ops._create_c_op(g, node_def, inputs);
-            NumOutputs = c_api.TF_OperationNumOutputs(_handle);
 
             _outputs = new Tensor[NumOutputs];
             for (int i = 0; i < NumOutputs; i++)

src/TensorFlowNET.Core/Operations/c_api.ops.cs

@@ -38,7 +38,7 @@ namespace Tensorflow
         public static extern IntPtr TF_NewOperation(IntPtr graph, string opType, string oper_name);
 
         [DllImport(TensorFlowLibName)]
-        public static extern string TF_OperationDevice(IntPtr oper);
+        public static extern IntPtr TF_OperationDevice(IntPtr oper);
 
         /// <summary>
         /// Sets `output_attr_value` to the binary-serialized AttrValue proto
@@ -50,13 +50,13 @@ namespace Tensorflow
         public static extern int TF_OperationGetAttrValueProto(IntPtr oper, string attr_name, IntPtr output_attr_value, IntPtr status);
 
         [DllImport(TensorFlowLibName)]
-        public static extern string TF_OperationName(IntPtr oper);
+        public static extern IntPtr TF_OperationName(IntPtr oper);
 
         [DllImport(TensorFlowLibName)]
         public static extern int TF_OperationNumInputs(IntPtr oper);
 
         [DllImport(TensorFlowLibName)]
-        public static extern string TF_OperationOpType(IntPtr oper);
+        public static extern IntPtr TF_OperationOpType(IntPtr oper);
 
         /// <summary>
         /// Get the number of control inputs to an operation.

src/TensorFlowNET.Core/Operations/ops.cs

@@ -30,12 +30,12 @@ namespace Tensorflow
             // Add inputs
             if(inputs != null && inputs.Count > 0)
             {
-                /*foreach (var op_input in inputs)
+                foreach (var op_input in inputs)
                 {
                     c_api.TF_AddInput(op_desc, op_input._as_tf_output());
-                }*/
+                }
 
-                c_api.TF_AddInputList(op_desc, inputs.Select(x => x._as_tf_output()).ToArray(), inputs.Count);
+                //c_api.TF_AddInputList(op_desc, inputs.Select(x => x._as_tf_output()).ToArray(), inputs.Count);
             }
 
             var status = new Status();

src/TensorFlowNET.Core/Status/Status.cs

@@ -15,7 +15,7 @@ namespace Tensorflow
         /// <summary>
         /// Error message
         /// </summary>
-        public string Message => c_api.TF_Message(_handle);
+        public string Message => c_api.StringPiece(c_api.TF_Message(_handle));
 
         /// <summary>
         /// Error code

src/TensorFlowNET.Core/Status/c_api.status.cs

@@ -12,7 +12,7 @@ namespace Tensorflow
         /// </summary>
         /// <param name="s"></param>
         [DllImport(TensorFlowLibName)]
-        public static unsafe extern void TF_DeleteStatus(IntPtr s);
+        public static extern void TF_DeleteStatus(IntPtr s);
 
         /// <summary>
         /// Return the code record in *s.
@@ -20,7 +20,7 @@ namespace Tensorflow
         /// <param name="s"></param>
         /// <returns></returns>
         [DllImport(TensorFlowLibName)]
-        public static extern unsafe TF_Code TF_GetCode(IntPtr s);
+        public static extern TF_Code TF_GetCode(IntPtr s);
 
         /// <summary>
         /// Return a pointer to the (null-terminated) error message in *s.
@@ -30,7 +30,7 @@ namespace Tensorflow
         /// <param name="s"></param>
         /// <returns></returns>
         [DllImport(TensorFlowLibName)]
-        public static extern unsafe string TF_Message(IntPtr s);
+        public static extern IntPtr TF_Message(IntPtr s);
 
         /// <summary>
         /// Return a new status object.

src/TensorFlowNET.Core/c_api.cs

@@ -12,20 +12,27 @@ namespace Tensorflow
     /// The API leans towards simplicity and uniformity instead of convenience
     /// since most usage will be by language specific wrappers.
     /// 
-    /// The params type mapping between .net and c_api
+    /// The params type mapping between c_api and .NET
     /// TF_XX** => ref IntPtr (TF_Operation** op) => (ref IntPtr op)
     /// TF_XX* => IntPtr (TF_Graph* graph) => (IntPtr graph)
     /// struct => struct (TF_Output output) => (TF_Output output)
+    /// struct* => struct (TF_Output* output) => (TF_Output[] output)
     /// const char* => string
     /// int32_t => int
     /// int64_t* => long[]
     /// size_t* => unlong[]
     /// void* => IntPtr
+    /// string => IntPtr c_api.StringPiece(IntPtr)
     /// </summary>
     public static partial class c_api
     {
         public const string TensorFlowLibName = "tensorflow";
 
+        public static string StringPiece(IntPtr handle)
+        {
+            return handle == IntPtr.Zero ? String.Empty : Marshal.PtrToStringAnsi(handle);
+        }
+
         public delegate void Deallocator(IntPtr data, IntPtr size, ref bool deallocator);
 
         [DllImport(TensorFlowLibName)]

src/TensorFlowNET.Core/tf.cs

@@ -37,7 +37,7 @@ namespace Tensorflow
             context.default_execution_mode = Context.EAGER_MODE;
         }
 
-        public static string VERSION => Marshal.PtrToStringAnsi(c_api.TF_Version());
+        public static string VERSION => c_api.StringPiece(c_api.TF_Version());
 
         public static Graph get_default_graph()
         {

test/TensorFlowNET.UnitTest/GraphTest.cs

@@ -39,17 +39,14 @@ namespace TensorFlowNET.UnitTest
             // Test not found errors in TF_Operation*() query functions.
             Assert.AreEqual(-1, c_api.TF_OperationOutputListLength(feed, "bogus", s));
             Assert.AreEqual(TF_Code.TF_INVALID_ARGUMENT, s.Code);
-            //Assert.IsFalse(c_test_util.GetAttrValue(feed, "missing", ref attr_value, s));
-            //Assert.AreEqual("Operation '' has no attr named 'missing'.", s.Message);
+            Assert.IsFalse(c_test_util.GetAttrValue(feed, "missing", ref attr_value, s));
+            Assert.AreEqual("Operation 'feed' has no attr named 'missing'.", s.Message);
 
             // Make a constant oper with the scalar "3".
             var three = c_test_util.ScalarConst(3, graph, s);
 
             // Add oper.
             var add = c_test_util.Add(feed, three, graph, s);
-
-            NodeDef node_def = null;
-            c_test_util.GetNodeDef(feed, ref node_def);
         }
     }
 }

test/TensorFlowNET.UnitTest/OperationsTest.cs

@@ -43,7 +43,7 @@ namespace TensorFlowNET.UnitTest
         public void addInConstant()
         {
             var a = tf.constant(4.0f);
-            var b = tf.placeholder(tf.float32);
+            var b = tf.constant(5.0f);
             var c = tf.add(a, b);
 
             using (var sess = tf.Session())

test/TensorFlowNET.UnitTest/c_test_util.cs

@@ -23,11 +23,13 @@ namespace TensorFlowNET.UnitTest
         {
             var desc = c_api.TF_NewOperation(graph, "AddN", name);
 
-            c_api.TF_AddInputList(desc, new TF_Output[]
+            var inputs = new TF_Output[]
             {
                 new TF_Output(l, 0),
                 new TF_Output(r, 0),
-            }, 2);
+            };
+
+            c_api.TF_AddInputList(desc, inputs, inputs.Length);
 
             op = c_api.TF_FinishOperation(desc, s);
             s.Check();