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 [email protected] 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 <[email protected]> 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;
>>
>> }
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "Protocol Buffers" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
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>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com
>>
>> <https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
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