I think the easiest thing would be that wherever you're now storing a google::protobuf::FieldDescriptor*, you can also store a google::protobuf::Message* pointing to the parent message.
On Tue, Jun 22, 2021 at 10:41 AM J G <[email protected]> wrote: > Hi Adam, > > Yes, the HealthReport variable is the parent, and it contains a > HardwareComponent variable, but I am enumerating the from the parent, > meaning I am trying to not hard-code the structure of the contained items. > > So how would I obtain a pointer to the message for each leaf without > hard-coding the member names in there? > > I am able to figure out what value I want to set in each leaf by a map I > have that uses the field's path to match it to the value I want to store. > > On Tuesday, 22 June 2021 at 13:33:11 UTC-4 [email protected] wrote: > >> So is it correct that HealthReport is the top-level message type and >> HardwareComponent is nested somewhere within that? I think what you're >> trying to do is doable, but when you call reflection->SetString(), you have >> to pass the immediate parent message containing the field, not the >> top-level message. You don't need to save the descriptor for each leaf, but >> you do need to save a pointer to the message containing each leaf. >> >> On Tue, Jun 22, 2021 at 10:17 AM J G <[email protected]> wrote: >> >>> 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 [email protected] 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 <[email protected]> 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 [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 email to [email protected]. >>>>>>> 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> >>>>>>> . >>>>>>> >>>>>> -- >>>>> 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 email to [email protected]. >>>>> >>>> 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> >>>>> . >>>>> >>>> -- >>> 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 email to [email protected]. >>> >> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/protobuf/39fd7a89-426a-453d-9482-4cb3e3658da0n%40googlegroups.com >>> <https://groups.google.com/d/msgid/protobuf/39fd7a89-426a-453d-9482-4cb3e3658da0n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- > 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 > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/protobuf/764459e6-6f37-42aa-869c-0f8405aa13c6n%40googlegroups.com > <https://groups.google.com/d/msgid/protobuf/764459e6-6f37-42aa-869c-0f8405aa13c6n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Protocol Buffers" group. 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