I believe I get the piece about constructing a message for a specific
type given a descriptor file.
About your last statement:
"If person.pb contains the serialized (binary) data for your proto,
you
should be using one of the Message::ParseFrom* routines. "
My understanding was I needed a "Person" object, before I could use
the "Parse" routines and hence I went through this trail of getting a
descriptor file and then constructing a Message(of type Person) and
then using that to Parse.
Are you saying that I do not need any descriptors etc at all. Given
ANY data file (which is a serialized proto buf file) I can use
Message::Parse and print it out ???
For e.g. I see that protoc --decode_raw < person.pb does indeed print
it out correctly (without any descriptor OR any .proto file), so I
think this may be possible.
In summary all I want to do is given ANY serialized message in a file,
I want to load it and print its contents out. That all.
Thanks again.
On Apr 2, 1:42 pm, Jason Hsueh <jas...@google.com> wrote:
> On Fri, Apr 2, 2010 at 9:13 AM, Navin <ng06d...@gmail.com> wrote:
> > 1. For the person example, I create a descriptor as follows:
> > "E:\Desktop\prototype_MAIN\protoc.exe" person.proto --
> > descriptor_set_out=msg.protocomp
>
> > 2. I create a Person object and serialized it to file. "person.pb"
>
> > 3. I want to write a program to "print" the Person object using ONLY
> > its descriptor. I know there is a way, but I cannot seem to get all
> > the APIs correct.
>
> > 4. Here is what I have done.
> > ifstream desc_file("E:\\Visual Studio 2008\\Projects\
> > \proto_buf1\\msg.protocomp",ios::in);
> > if (desc_file.bad()) {
> > std::cout << "desc file not read...exiting" << std::endl;
> > return -1;
> > }
>
> > FileDescriptorSet f;
> > f.ParseFromIstream(&desc_file);
>
> f.PrintDebugString();
>
>
>
> > FileDescriptorProto fdp = f.file(0);
> > fdp.PrintDebugString();
>
> > DescriptorProto dp = fdp.message_type(0);
> > dp.PrintDebugString();
>
> > Now what ? I need a copy of "Message" that I can pass as input to
> > Parse, I think. I also may need DynamicMessage etc, and possibly also
> > the following:
>
> Yes, you should construct a DynamicMessage. To do this, you'll need to build
> the descriptor protos into a pool. For instance:
>
> DescriptorPool descriptor_pool;
> for (int i = 0; i < f.file_size(); ++i) {
> descriptor_pool.BuildFile(f.file(i));}
>
> const Descriptor* descriptor = descriptor_pool.FindMessageTypeByName("...");
> DynamicMessageFactory factory;
> Message* my_message = factory.GetPrototype(descriptor)->New();
> ...
> delete my_message;
>
> (You should probably check the return values of most of these calls -
> BuildFile() may return NULL, for instance. You also probably want to have
> some mechanism for specifying the message type, since you generally won't be
> able to assume that it's the first message in the first file)
>
>
>
> > ifstream input_file("E:\\Visual Studio 2008\\Projects\
> > \proto_buf1\\Debug\\person.pb",ios::in);
> > if (input_file.bad()) {
> > std::cout << "file not read...exiting" << std::endl;
> > return -1;
> > }
>
> > IstreamInputStream is(&input_file);
>
> > TextFormat::Parse(&is,(msg));
>
> If person.pb contains the serialized (binary) data for your proto, you
> should be using one of the Message::ParseFrom* routines.
>
> > msg->PrintDebugString();
>
> > Any simple example is GREATLY appreciated. Thanks.
>
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