[MXNET-1083] Add the example to demonstrate the inference workflow us…

…ing C++ API (#13294)

* [MXNET-1083] Add the example to demonstrate the inference workflow using C++ API

* [MXNET-1083] Add the example to demonstrate the inference workflow using C++ API

* Updated the code to address the review comments.

* Added the README file for the folder.

* Addressed the review comments

* Addressed the review comments to use argmax and default mean values.

cpp-package/example/README.md

@@ -2,7 +2,8 @@
 
 ## Building C++ examples
 
-The examples are built while building the MXNet library and cpp-package from source . However, they can be built manually as follows
+The examples in this folder demonstrate the **training** workflow. The **inference workflow** related examples can be found in [inference](</~https://github.com/apache/incubator-mxnet/blob/master/cpp-package/example/inference>) folder.
+The examples in this folder are built while building the MXNet library and cpp-package from source . However, they can be built manually as follows
 
 From cpp-package/examples directory
 
@@ -18,7 +19,7 @@ The examples that are built to be run on GPU may not work on the non-GPU machine
 The makefile will also download the necessary data files and store in a data folder. (The download will take couple of minutes, but will be done only once on a fresh installation.)
 
 
-## Examples
+## Examples demonstrating training workflow
 
 This directory contains following examples. In order to run the examples, ensure that the path to the MXNet shared library is added to the OS specific environment variable viz. **LD\_LIBRARY\_PATH** for Linux, Mac and Ubuntu OS and **PATH** for Windows OS. For example `export LD_LIBRARY_PATH=/usr/local/cuda/lib64:/home/ubuntu/incubator-mxnet/lib` on ubuntu using gpu.
 

cpp-package/example/inference/Makefile

@@ -0,0 +1,40 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+
+CPPEX_SRC = $(wildcard *.cpp)
+CPPEX_EXE = $(patsubst %.cpp, %, $(CPPEX_SRC))
+OPENCV_CFLAGS=`pkg-config --cflags opencv`
+OPENCV_LDFLAGS=`pkg-config --libs opencv`
+
+CXX=g++
+
+
+CFLAGS=$(COMMFLAGS) -I../../../3rdparty/tvm/nnvm/include -I../../../3rdparty/dmlc-core/include -I ../../include -I ../../../include -Wall -O3 -msse3 -funroll-loops -Wno-unused-parameter -Wno-unknown-pragmas
+CPPEX_EXTRA_LDFLAGS := -L../../../lib -lmxnet $(OPENCV_LDFLAGS)
+
+all: $(CPPEX_EXE)
+
+debug: CPPEX_CFLAGS += -DDEBUG -g
+debug: all
+
+
+$(CPPEX_EXE):% : %.cpp
+	$(CXX) -std=c++0x $(CFLAGS)  $(CPPEX_CFLAGS) -o $@ $(filter %.cpp %.a, $^) $(CPPEX_EXTRA_LDFLAGS)
+
+clean:
+	rm -f $(CPPEX_EXE)

cpp-package/example/inference/README.md

@@ -0,0 +1,41 @@
+# MXNet C++ Package Inference Workflow Examples
+
+## Building C++ Inference examples
+
+The examples in this folder demonstrate the **inference** workflow.
+To build examples use following commands:
+
+-  Release: **make all**
+-  Debug: **make debug all**
+
+
+## Examples demonstrating inference workflow
+
+This directory contains following examples. In order to run the examples, ensure that the path to the MXNet shared library is added to the OS specific environment variable viz. **LD\_LIBRARY\_PATH** for Linux, Mac and Ubuntu OS and **PATH** for Windows OS.
+
+### [inception_inference.cpp](</~https://github.com/apache/incubator-mxnet/blob/master/cpp-package/example/inference/inception_inference.cpp>)
+
+This example demonstrates image classification workflow with pre-trained models using MXNet C++ API. The command line parameters the example can accept are as shown below:
+
+```
+./inception_inference --help
+Usage:
+inception_inference --symbol <model symbol file in json format>
+                    --params <model params file>
+					--image <path to the image used for prediction
+					--synset file containing labels for prediction
+					[--input_shape <dimensions of input image e.g "3 224 224"]
+					[--mean file containing mean image for normalizing the input image
+					[--gpu] Specify this option if workflow needs to be run in gpu context
+```
+The model json and param file and synset files are required to run this example.  The sample command line is as follows:
+
+```
+
+./inception_inference --symbol "./model/Inception-BN-symbol.json" --params "./model/Inception-BN-0126.params" --synset "./model/synset.txt" --mean "./model/mean_224.nd" --image "./model/dog.jpg"
+```
+Alternatively, The script [unit_test_inception_inference.sh](</~https://github.com/apache/incubator-mxnet/blob/master/cpp-package/example/inference/unit_test_inception_inference.sh>) downloads the pre-trained **Inception** model and a test image. The users can invoke this script as follows:
+
+```
+./unit_test_inception_inference.sh
+```