Fix predict c api

[howard0su]

Fix the regression in predict_api. While I am here, update and cleanup the C++ image classification example.

[piiswrong]

why change this？

[howard0su]

Fixed Eric Junyuan Xie <notifications@github.com>于2017年1月6日 周五上午1:20写道：

***@***.**** commented on this pull request. ------------------------------ In example/image-classification/predict-cpp/Makefile <#4537 (review)>: > image-classification-predict.o: image-classification-predict.cc - g++ -O3 -c image-classification-predict.cc ${CFLAGS} + g++ -O0 -c image-classification-predict.cc ${CFLAGS} why change this？ — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#4537 (review)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAuzRDI743_MQymgDXu0Td6pTZxFBHlEks5rPSZxgaJpZM4LbfFy> . --

-Howard

[songtianyi]

This pr haven't been merged yet? Waiting merging to test.

[Piyush3dB]

@piiswrong I get the following errors when I load symbol from JSON file using the _LIB.MXSymbolCreateFromFile() function

[14:35:44] mxnet/dmlc-core/include/dmlc/./logging.h:300: [14:35:44] src/core/op.cc:55: Check failed: op != nullptr Operator Convolution is not registered
[14:47:36] mxnet/dmlc-core/include/dmlc/./logging.h:300: [14:47:36] src/core/op.cc:55: Check failed: op != nullptr Operator FullyConnected is not registered

Is this a known issue or could I be doing something wrong?

If I construct the same symbol using mx.symbol.* objects then I don't get any error when I execute the symbol.

[Piyush3dB]

To get rid of the errors I'm seeing above, I have to first call the function _LIB.MXListAllOpNames() before calling _LIB.MXSymbolCreateFromFile(). All is good and working for me now.