Hi again Adam, and thank you for taking the time to help me.
Maybe I haven't explained what I am trying to do properly.
I have a protobuf variable, which itself is composed of more nested
variables.
I am enumerating the fields of the variable.
Where the item is a leaf, the field is a simple c-like type (int, bool,
string, etc)
Where the item itself has fields, it is an agglomerate type and it is
descended recursively.
My aim is to set each leaf programmatically.
So as I traverse the arborescance, I am collecting the field definitions
for the leafs.
So later, I am addressing the variable again, but trying to set one of its
leafs by the field definition I saved. Do I also have to save the
descriptor for each leaf?
Can what I want to do be done?
On Tuesday, 22 June 2021 at 11:52:00 UTC-4 acoz...@google.com wrote:
> It looks to me like r->report points to a vafmsg.HealthReport but the
> field descriptor refers to a field in another message
> (vafmsg.HardwareComponent).
>
> On Tue, Jun 22, 2021 at 7:42 AM J G <prog...@gmail.com> wrote:
>
>> Hello Adam,
>>
>> OK, I understand, so I've tried this, but I get an error.
>>
>> void my_set_value( class healthreport * r, const char * defaultvalue,
>> const google::protobuf::FieldDescriptor * descriptor ) {
>>
>> auto reflection = r->report->GetReflection();
>>
>> switch( descriptor->type() ) {
>> case google::protobuf::FieldDescriptor::TYPE_STRING: {
>>
>> printf( "REQUESTED TYPE: STRING" EOL );
>> std::string s = defaultvalue;
>> reflection->SetString( r->report, descriptor, s );
>>
>> }
>> break;
>>
>> default:
>>
>> printf( "REQUESTED TYPE %d NOT HANDLED" EOL,
>> descriptor->type() );
>> break;
>>
>> }
>>
>> }
>> Running the above produces the following output:
>>
>> REQUESTED TYPE: STRING
>> [libprotobuf FATAL
>> /var/tmp/portage/dev-libs/protobuf-3.15.8/work/protobuf-3.15.8/src/google/protobuf/generated_message_reflection.cc:111]
>>
>> Protocol Buffer reflection usage error:
>> Method : google::protobuf::Reflection::SetString
>> Message type: vafmsg.HealthReport
>> Field : vafmsg.HardwareComponent.hardware_interface
>> Problem : Field does not match message type.
>> terminate called after throwing an instance of
>> 'google::protobuf::FatalException'
>> what(): Protocol Buffer reflection usage error:
>> Method : google::protobuf::Reflection::SetString
>> Message type: vafmsg.HealthReport
>> Field : vafmsg.HardwareComponent.hardware_interface
>> Problem : Field does not match message type.
>>
>> Here is the proto definition of the variable triggering the exception:
>>
>> message HardwareComponent {
>> optional Component component = 1;
>> repeated DiscreteValue temp = 2;
>> optional string hardware_interface = 3;
>> optional uint32 remaining_life = 4;
>> optional uint32 total_hours = 5;
>> optional EnergyInfo energy = 6;
>> }
>>
>> So the type really IS string, yet an exception is triggered...
>>
>> What am I doing wrong?
>>
>> On Friday, 18 June 2021 at 17:56:57 UTC-4 acoz...@google.com wrote:
>>
>>> Each descriptor describes part of the schema (e.g. a message type, enum
>>> type, etc.) but is unrelated to any particular instance of it. As a result,
>>> if you have a descriptor by itself then you can't really modify anything
>>> because you separately need an instance of the thing you want to modify.
>>> The way to programmatically modify a message is to use the Reflection
>>> <https://github.com/protocolbuffers/protobuf/blob/9d9d8ee18dedfb18371031cd299d1d282ddf707f/src/google/protobuf/message.h#L452>
>>>
>>> API. You can use Reflection::ListFields() to get a list of all the fields
>>> that are set on the message and then there are Reflection::Get* and
>>> Reflection::Set* methods to get and set particular fields.
>>>
>>> On Fri, Jun 18, 2021 at 9:11 AM J G <prog...@gmail.com> wrote:
>>>
>>>> Hi,
>>>>
>>>> I've got some code that lets me recursively walk a protobuf variable.
>>>>
>>>> That part works, I can enumerate the characteristics of a variable, but
>>>> the pointers/references returned by the API are const.
>>>>
>>>> My question is: From a variable's Descriptor or FieldDescriptor, is it
>>>> possible to get a non-const pointer/reference to the field to be able to
>>>> modify it?
>>>>
>>>> Here's my (simplified) code so far:
>>>>
>>>> void enumpb( const google::protobuf::Descriptor * d ) {
>>>>
>>>> for ( int i = 0; i < d->field_count(); i++ ) {
>>>>
>>>> auto field = d->field( i );
>>>>
>>>> // Modify variable code here
>>>> [...]
>>>>
>>>> auto mt = field->message_type();
>>>> if ( ! mt ) {
>>>> continue;
>>>> } else if ( 0 != strcmp( d->full_name().c_str(),
>>>> mt->full_name().c_str() ) ) {
>>>>
>>>> enumpb( mt ) ;
>>>>
>>>> }
>>>>
>>>> }
>>>>
>>>> return true;
>>>>
>>>> }
>>>>
>>>> --
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>>>>
>>>> <https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>> .
>>>>
>>> --
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> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/protobuf/7ef6e77e-8635-4b16-b570-b80f75d207d9n%40googlegroups.com
>>
>> <https://groups.google.com/d/msgid/protobuf/7ef6e77e-8635-4b16-b570-b80f75d207d9n%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
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