CODEWITHSUNDEEP
c++protocol-buffers
JTejedor
JTejedor

Reputation: 1134

Set oneof in a protobuf message using reflection

After a few hours, I still can not set a oneof field in a clear (just created) protobuf message using reflection in c++.

I can obtain the needed OneOfDescriptor through the Descriptor of the message. But when I try to 'set' the oneof using Reflection, I found the real problem. There is only three function members related to OneOfDescriptor:

So there is not a SetOneofFieldDescriptorand if the oneof in the message is not previously defined, using a mutable_XXXX function member in the message, the GetOneofFieldDescriptor returns nullptr.

Therefore I am really stuck and any idea will be welcome.

Thanks in advance.

Upvotes: 1

Views: 4844

Answers (1)

Miles Budnek
Miles Budnek

Reputation: 30494

You set it the same way you would set the field if it weren't part of a oneof. Get a FieldDescriptor from the message's Descriptor and pass it to the appropriate SetXXX method of the message's Reflection.

Given a message like the following:

message Foo
{
    oneof bar
    {
        int32 a = 1;
        string b = 2;
    }
}

You can set the a member as follows:

#include "foo.pb.h"

int main()
{
    Foo f;
    const google::protobuf::Descriptor* d = f.GetDescriptor();
    const google::protobuf::FieldDescriptor* a = d->FindFieldByName("a");

    const google::protobuf::Reflection* r = f.GetReflection();
    r->SetInt32(&f, a, 42);
}

Protobuf will take care of making sure any previously set members of the oneof get unset as needed.

Upvotes: 3

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