Can't read nested maps (raises YAML::InvalidScalar)

Question

I have a class (contains a few scalar values and a vector of floats) and I want to read and write an instance as the value of another map.

    
// write

 out << YAML::Key << "my_queue" << YAML::Value << my_queue;



// read (other code cut out...)
 for (YAML::Iterator it=doc.begin();it!=doc.end();++it)
  {
    std::string key, value;
    it.first() >> key;
    it.second() >> value;
    if (key.compare("my_queue") == 0) {
      *it >> my_queue;
    }
 }

Writing this class works perfectly, but I can't seem to read it no matter what I do. It keeps throwing an InvalidScalar.

Caught YAML::InvalidScalar  yaml-cpp: error at line 20, column 13: invalid scalar

and this is that the output (written with yaml-cpp without it reporting any errors) looks like:

Other Number: 80
my_queue:
  size: 20
  data:
    - 3.5
    - -1
    - -1.5
    - 0.25
    - -24.75
    - -5.75
    - 2.75
    - -33.55
    - 7.25
    - -11
    - 15
    - 37.5
    - -3.75
    - -28.25
    - 18.5
    - 14.25
    - -36.5
    - 6.75
    - -0.75
    - 14
  max_size: 20
  mean: -0.0355586
  stdev: 34.8981
even_more_data: 1277150400

The documentation seems to say this is supported usage, a nested map, in this case with a sequence as one of the values. It complains about it being an InvalidScalar, even though the first thing I do it tell it that this is a map:

YAML::Emitter& operator << ( YAML::Emitter& out, const MeanStd& w )
{
  out << YAML::BeginMap;
  out << YAML::Key << "size";
  out << YAML::Value << w.size();

  out << YAML::Key << "data";
  out << YAML::Value << YAML::BeginSeq;
  for(Noor::Number i=0; i<w.size(); ++i) {
    out << w[i];
  }
  out << YAML::EndSeq;
  out << YAML::Key << "max_size";
  out << YAML::Value << w.get_max_size();
  out << YAML::Key << "mean";
  out << YAML::Value << w.mean();
  out << YAML::Key << "stdev";
  out << YAML::Value << w.stdev();

  out << YAML::EndMap;
  return out;
}

Does anyone see a problem with this?

Answer 1

When you're reading the YAML:

std::string key, value;
it.first() >> key;
it.second() >> value; // ***
if (key.compare("my_queue") == 0) {
  *it >> my_queue;
}

The marked line tries to read the value of the key/value pair as a scalar (std::string); that's why it tells you that it's an invalid scalar. Instead, you want:

std::string key, value;
it.first() >> key;
if (key.compare("my_queue") == 0) {
  it.second() >> my_queue;
} else {
  // ...
  // for example: it.second() >> value;
}