Converting Caffe caffe::Datum to OpenCV cv::Mat in C++

[Kevin]

I'm doing some debugging and so I'm dumping image files to look at the predictions and transformations.

I can create a caffe::Datum from cv::Mat:

cv::Mat matrix;
// ... initialize matrix
caffe::Datum datum;
caffe::CVMatToDatum(matrix, &datum)

but how do I create a cv::Mat from caffe::Datum? The following code gives the fatal exception "Datum not encoded":

caffe::Datum datum;
// ... initialize datum
cv::Mat matrix;
matrix = DecodeDatumToCVMat(datum, true);