How to read Protobuf oneof message using C++?

Question

Consider a simple Protobuf code like this:

message MessageName
{
  oneof some_options {
    OptionA optionAName = 1;
    OptionB optionBName = 2;
  }
}

This will generate the following C++ code (or something like it, I've renamed some variables manually so it may not be 100% right):

typedef struct _namespace_name_MessageName {
    pb_size_t which_some_options;
    union {
        namespace_name_OptionA optionAName;
        namespace_name_OptionB optionBName;
    } some_options;
} namespace_name_MessageName;

How do I read this message in C++? I would like to say "if it is OptionA, do this" and "if it is OptionB, do this". I haven't been able to find out how which_some_options works though, I can't find it in the documentation at all. I did read this but I can't find any of the methods mentioned there in the code that Protobuf generated. An example that shows how I should accomplish what I'm trying to accomplish would be greatly appreciated.

Answer 1

The original author discovered they were using NanoPB, and therefore the generated code did not match Google's C++ protobuf docs.

However, for those looking for a quick example on how to read oneof using C++ code, it should look something like this:

void ParseMessageName(MessageName msg) 
{
  switch (msg.some_options_case()) {
    case MessageName::SomeOptionsCase::kOptionAName: {
      // The msg contained "optionAName"
      break;
    }
    case MessageName::SomeOptionsCase::kOptionBName: {
      // The msg contained "optionBName"
      break;
    }
    default: {
      break;
    }
  }
}

The oneof section of the docs is here