Read value of enum extension in protocol buffer

Question

I just asked this question and have resolved to write an extension for enum values in my protocol buffer. However I am having an extremely difficult time actually reading the values back, even with this simple .proto file: ``` package test; import "google/protobuf/descriptor.proto"; extend google.protobuf.EnumValueOptions { optional string abbr = 54321; } message Person { required string name = 1; required int32 id = 2; optional string email = 3; enum PhoneType { MOBILE = 0 [(abbr)="Mobile ph"]; HOME = 1 [(abbr)="HomePhone"]; WORK = 2 [(abbr)="Work number"]; } message PhoneNumber { required string number = 1; optional PhoneType type = 2 [default = HOME]; } repeated PhoneNumber phone = 4; } message AddressBook { repeated Person person = 1; } ``` I've been trying these and other variants: ``` test::Person::PhoneNumber::descriptor()->options().GetExtension(test::abbr); test::Person::PhoneNumber::descriptor().GetExtension(test::abbr); test::Person::descriptor()->options().GetExtension(tes…

Accepted Answer

It's a wee bit convoluted, but you need to get the `EnumValueDescriptor` for the phone type, and then call `options().GetExtension(test::abbr)` on this.

For example:

```
test::Person person;
person.set_name("Caol Ila");
person.set_id(1);

test::Person::PhoneNumber *phone = person.add_phone();
phone->set_number("01496 840207");
phone->set_type(test::Person::MOBILE);

phone = person.add_phone();
phone->set_number("01496 840207");
phone->set_type(test::Person::HOME);

phone = person.add_phone();
phone->set_number("01496 840207");
phone->set_type(test::Person::WORK);

phone = person.add_phone();
phone->set_number("01496 840207");

const google::protobuf::EnumDescriptor* enum_desc =
    test::Person::PhoneType_descriptor();
std::string value;

for (int phone_index = 0; phone_index < person.phone_size(); ++phone_index) {
  if (person.phone(phone_index).has_type()) {
    int phone_type = person.phone(phone_index).type();
    value = enum_desc->value(phone_type)->options().GetExtension(test::abbr);
  }
}
```

Read value of enum extension in protocol buffer

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