PR: Run C++ torchvision example as part of cmake tests (#2678)

* Run C++ torchvision example as part of cmake tests

* Enable C++14 support

* Minor error correction

* Add GPU forward on example

* Use arrow operator

examples/cpp/hello_world/CMakeLists.txt

@@ -11,4 +11,6 @@ add_executable(hello-world main.cpp)
 # We now need to link the TorchVision library to our executable.
 # We can do that by using the TorchVision::TorchVision target,
 # which also adds all the necessary torch dependencies.
+target_compile_features(hello-world PUBLIC cxx_range_for)
 target_link_libraries(hello-world TorchVision::TorchVision)
+set_property(TARGET hello-world PROPERTY CXX_STANDARD 14)

examples/cpp/hello_world/main.cpp

 #include <iostream>
-
 #include <torchvision/models/resnet.h>
 
 int main()
@@ -11,5 +10,14 @@ int main()
   auto in = torch::rand({1, 3, 10, 10});
   auto out = model->forward(in);
 
-  std::cout << out;
+  std::cout << out.sizes();
+
+  if (torch::cuda::is_available()) {
+    // Move model and inputs to GPU
+    model->to(torch::kCUDA);
+    auto gpu_in = in.to(torch::kCUDA);
+    auto gpu_out = model->forward(gpu_in);
+
+    std::cout << gpu_out.sizes();
+  }
 }

packaging/build_cmake.sh

@@ -61,7 +61,7 @@ popd
 python setup.py develop
 
 # Trace, compile and run project that uses Faster-RCNN
-cd test/tracing/frcnn
+pushd test/tracing/frcnn
 mkdir build
 
 # Trace model
@@ -81,3 +81,21 @@ fi
 
 # Run traced program
 ./test_frcnn_tracing
+
+# Compile and run the CPP example
+popd
+cd examples/cpp/hello_world
+
+mkdir build
+cd build
+cmake .. -DTorch_DIR=$TORCH_PATH/share/cmake/Torch
+
+if [[ "$OSTYPE" == "msys" ]]; then
+    "$script_dir/windows/internal/vc_env_helper.bat" "$script_dir/windows/internal/build_cpp_example.bat"
+    cd Release
+else
+    make
+fi
+
+# Run CPP example
+./hello-world

packaging/windows/internal/build_cpp_example.bat

+@echo on
+set CL=/I"C:\Program Files (x86)\torchvision\include"
+msbuild "-p:Configuration=Release" hello-world.vcxproj