Cleaned up image classification cpp example (apache#9799)

* Cleaned up cpp image classification example

* Added gpg key

* Revert "Added gpg key"

This reverts commit d5c29d7.

* Adressed review comments, made other small improvements

* Reverted default device type to cpu

* Minor type change

* Applied review comments

* Brought back the static linking option

CMakeLists.txt

@@ -32,6 +32,7 @@ mxnet_option(USE_GPROF            "Compile with gprof (profiling) flag" OFF)
 mxnet_option(USE_CXX14_IF_AVAILABLE "Build with C++14 if the compiler supports it" OFF)
 mxnet_option(USE_VTUNE            "Enable use of Intel Amplifier XE (VTune)" OFF) # one could set VTUNE_ROOT for search path
 mxnet_option(ENABLE_CUDA_RTC      "Build with CUDA runtime compilation support" ON)
+mxnet_option(BUILD_CPP_EXAMPLES   "Build cpp examples" ON)
 mxnet_option(INSTALL_EXAMPLES     "Install the example source files." OFF)
 mxnet_option(USE_SIGNAL_HANDLER   "Print stack traces on segfaults." OFF)
 
@@ -690,8 +691,7 @@ if(USE_CPP_PACKAGE)
   add_subdirectory(cpp-package)
 endif()
 
-# Problems on Mac OS X: 1. librt not available 2. mxnet built as MODULE library, which can't be linked.
-if(NOT (${CMAKE_SYSTEM_NAME} STREQUAL "Darwin"))
+if(BUILD_CPP_EXAMPLES)
   add_subdirectory(example/image-classification/predict-cpp)
 endif()
 

example/image-classification/predict-cpp/CMakeLists.txt

@@ -1,34 +1,36 @@
-if(USE_OPENCV)
-  find_package(OpenCV QUIET COMPONENTS core highgui imgproc imgcodecs)
-  if(NOT OpenCV_FOUND) # if not OpenCV 3.x, then imgcodecs are not found
-    find_package(OpenCV REQUIRED COMPONENTS core highgui imgproc)
-  endif()
+# Check OpenCV
+if(NOT USE_OPENCV OR NOT OpenCV_FOUND)
+  message(WARNING "\
+OpenCV should be enabled and found to build image classification example, skipping...")
+  return()
+endif()
 
-  if(NOT MSVC)
-    set(UNITTEST_STATIC_LINK ON)
-  endif()
+if(NOT MSVC)
+  set(IMG_CLASSIFICATION_EXAMPLE_STATIC_LINK ON CACHE BOOL "\
+Link mxnet library statically in the c++ image classification example")
+else()
+  # disable static linking on Windows
+  set(IMG_CLASSIFICATION_EXAMPLE_STATIC_LINK OFF)
+endif()
 
-  add_executable(image-classification-predict image-classification-predict.cc)
-  include_directories(SYSTEM ${OpenCV_INCLUDE_DIRS})
+add_executable(image-classification-predict image-classification-predict.cc)
+include_directories(SYSTEM ${OpenCV_INCLUDE_DIRS})
 
-  if(UNITTEST_STATIC_LINK)
-    target_link_libraries(image-classification-predict
-      ${BEGIN_WHOLE_ARCHIVE} mxnet_static ${END_WHOLE_ARCHIVE}
-      dmlc
-      ${mxnet_LINKER_LIBS}
-      )
-  else()
-    target_link_libraries(image-classification-predict
-      dmlc
-      ${nnvm_LINKER_LIBS}
-      ${mxnet_LINKER_LIBS}
-      mxnet
-      )
-  endif()
-  target_link_libraries(image-classification-predict ${OpenCV_LIBS})
-  if(UNIX)
-      target_link_libraries(image-classification-predict rt)
-  endif()
-  list(APPEND mxnet_LINKER_LIBS ${OpenCV_LIBS})
+if(IMG_CLASSIFICATION_EXAMPLE_STATIC_LINK)
+  target_link_libraries(image-classification-predict
+                        ${BEGIN_WHOLE_ARCHIVE} mxnet_static ${END_WHOLE_ARCHIVE}
+                        dmlc
+                        ${mxnet_LINKER_LIBS}
+                        )
+  add_dependencies(image-classification-predict mxnet_static)
+else()
+  target_link_libraries(image-classification-predict
+                        dmlc
+                        ${nnvm_LINKER_LIBS}
+                        ${mxnet_LINKER_LIBS}
+                        mxnet
+                        )
+  add_dependencies(image-classification-predict mxnet)
 endif()
 
+