I have a simple csv file that I am trying to read using protobuf. For some reason it fails at ParseFromIstream

test-data.csv

col1 col2 col3 
1 2 3

 fstream in("/input/test-data.csv", ios::in | ios::binary);

  if (!in) {
        std::cerr << "Failed to open file." << std::endl;
         return 1;
  }

  modelspec::v1::ParameterValue pv;            

  if (!pv.ParseFromIstream(&in)) {
       std::cerr << "Failed to parse protobuf data." << std::endl;
       return 1;
  }

Protofile definition is below

message ParameterValue {
    // Name of the parameter
    string name = 1;
    // Value of the parameter
    oneof value {
        string stringValue = 2;
        int64 intValue = 3;
        FixedPrecision fixedPrecisionValue = 4;
     }

}