Re: [protobuf] Enumerating a variable's fields and setting them

[J G]

Hello again, Adam,

If I understand you correctly, the key would be to obtain the 
mutable-message (by name) for the child from the parent as I descend the 
tree.

It think that would work!
Thank you very much for your light, I'm a newbie to protobuf and this 
demystifies part of it. I'll see if I can get that working
Thanks again

On Tuesday, 22 June 2021 at 14:49:20 UTC-4 acoz...@google.com wrote:

> Here's how you could set that nested field in your example (this code is 
> untested so may not work exactly, but should be pretty close):
>
> const FieldDescriptor* health_report_field = 
> parent.GetDescriptor()->FindFieldByName("healthreport");
> Message* health_report = parent.GetReflection()->MutableMessage(, 
> health_report_field);
> const FieldDescriptor* os_field = 
> health_report->GetDescriptor()->FieldFieldByName("os");
> Message* os = 
> health_report->GetReflection()->MutableMessage(health_report, os_field);
> const FieldDescriptor* version_field = 
> os->GetDescriptor()->FindFieldByName("version");
> os->GetReflection()->SetEnumValue(os, version_field, 3);
>
> On Tue, Jun 22, 2021 at 11:34 AM J G  wrote:
>
>> Hi Adam,
>>
>> OK, but would I need to know the fields in the message ahead of time? 
>> That is what I am trying to avoid.
>> The paths of the nested messages are in a table, such as
>>
>> "healthreport/os/version", 3
>>
>> So the healthreport variable is allocated, and it contains a component 
>> called os, which itself contains a field called version.
>>
>> So I am trying to write a generic enum function, that can descend the 
>> parent, and guided by the path info, can resolve the value that needs to be 
>> stored there, but if I am to traverse the entire tree manually, how does 
>> the reflection API help?
>> On Tuesday, 22 June 2021 at 14:21:59 UTC-4 acoz...@google.com wrote:
>>
>>> I think the reason this is getting tricky is because you're trying to 
>>> traverse the descriptors first and then look at the message tree afterward. 
>>> I would expect it to be much easier if you traverse the message and look at 
>>> the descriptors at the same time.
>>>
>>> On Tue, Jun 22, 2021 at 10:58 AM J G  wrote:
>>>
 Hi Adam,

 That works for the first iteration, but I descend the tree like so: 

 bool enumpb( const char * pszpath, ENUMPROTOPROC f, const 
 google::protobuf::Descriptor * d, uintptr_t param ) {

 std::string path = pszpath;

 for ( int i = 0; i < d->field_count(); i++ ) {

 auto field = d->field( i );

 std::string localpath = pszpath;

 if ( 0 != strcmp( "component", field->name().c_str() ) ) {

 localpath.append( field->name() );

 }

 if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {

 if ( f && ! f( field, localpath.c_str(), param ) ) {

 return false;

 }

 }

 auto mt = field->message_type();

 if ( ! mt ) {

 continue;

 } else if ( 0 != strcmp( d->full_name().c_str(), 
 mt->full_name().c_str() ) ) {

 std::string localpath2 = localpath;

 if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) 
 ) {

 localpath2.append( "/" );

 }

 if ( ! enumpb( hp, report, localpath2.c_str(), f, mt, param 
 ) ) {

 return false;

 }

 } else {

 //printf( "Skipping circular %s" EOL, 
 d->full_name().c_str() );

 }

 }

 return true;

 }

 So I start the traversal like this:

 auto d = report->GetDescriptor();

 enumpb( "", f, d, param );

 And it goes down the variable, visiting each leaf and nested child 
 variable, but I can't address each nested child directly that way, can I?
 The mt variable does hold the descriptor for each nested variable at 
 some point, but I don't know how I'd derive the variable's instance from 
 it.

 On Tuesday, 22 June 2021 at 13:47:15 UTC-4 acoz...@google.com wrote:

> 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  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 

Re: [protobuf] Enumerating a variable's fields and setting them

['Adam Cozzette' via Protocol Buffers]

Here's how you could set that nested field in your example (this code is
untested so may not work exactly, but should be pretty close):

const FieldDescriptor* health_report_field =
parent.GetDescriptor()->FindFieldByName("healthreport");
Message* health_report = parent.GetReflection()->MutableMessage(,
health_report_field);
const FieldDescriptor* os_field =
health_report->GetDescriptor()->FieldFieldByName("os");
Message* os = health_report->GetReflection()->MutableMessage(health_report,
os_field);
const FieldDescriptor* version_field =
os->GetDescriptor()->FindFieldByName("version");
os->GetReflection()->SetEnumValue(os, version_field, 3);

On Tue, Jun 22, 2021 at 11:34 AM J G  wrote:

> Hi Adam,
>
> OK, but would I need to know the fields in the message ahead of time? That
> is what I am trying to avoid.
> The paths of the nested messages are in a table, such as
>
> "healthreport/os/version", 3
>
> So the healthreport variable is allocated, and it contains a component
> called os, which itself contains a field called version.
>
> So I am trying to write a generic enum function, that can descend the
> parent, and guided by the path info, can resolve the value that needs to be
> stored there, but if I am to traverse the entire tree manually, how does
> the reflection API help?
> On Tuesday, 22 June 2021 at 14:21:59 UTC-4 acoz...@google.com wrote:
>
>> I think the reason this is getting tricky is because you're trying to
>> traverse the descriptors first and then look at the message tree afterward.
>> I would expect it to be much easier if you traverse the message and look at
>> the descriptors at the same time.
>>
>> On Tue, Jun 22, 2021 at 10:58 AM J G  wrote:
>>
>>> Hi Adam,
>>>
>>> That works for the first iteration, but I descend the tree like so:
>>>
>>> bool enumpb( const char * pszpath, ENUMPROTOPROC f, const
>>> google::protobuf::Descriptor * d, uintptr_t param ) {
>>>
>>> std::string path = pszpath;
>>>
>>> for ( int i = 0; i < d->field_count(); i++ ) {
>>>
>>> auto field = d->field( i );
>>>
>>> std::string localpath = pszpath;
>>>
>>> if ( 0 != strcmp( "component", field->name().c_str() ) ) {
>>>
>>> localpath.append( field->name() );
>>>
>>> }
>>>
>>> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {
>>>
>>> if ( f && ! f( field, localpath.c_str(), param ) ) {
>>>
>>> return false;
>>>
>>> }
>>>
>>> }
>>>
>>> auto mt = field->message_type();
>>>
>>> if ( ! mt ) {
>>>
>>> continue;
>>>
>>> } else if ( 0 != strcmp( d->full_name().c_str(),
>>> mt->full_name().c_str() ) ) {
>>>
>>> std::string localpath2 = localpath;
>>>
>>> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() )
>>> ) {
>>>
>>> localpath2.append( "/" );
>>>
>>> }
>>>
>>> if ( ! enumpb( hp, report, localpath2.c_str(), f, mt, param
>>> ) ) {
>>>
>>> return false;
>>>
>>> }
>>>
>>> } else {
>>>
>>> //printf( "Skipping circular %s" EOL, d->full_name().c_str()
>>> );
>>>
>>> }
>>>
>>> }
>>>
>>> return true;
>>>
>>> }
>>>
>>> So I start the traversal like this:
>>>
>>> auto d = report->GetDescriptor();
>>>
>>> enumpb( "", f, d, param );
>>>
>>> And it goes down the variable, visiting each leaf and nested child
>>> variable, but I can't address each nested child directly that way, can I?
>>> The mt variable does hold the descriptor for each nested variable at
>>> some point, but I don't know how I'd derive the variable's instance from it.
>>>
>>> On Tuesday, 22 June 2021 at 13:47:15 UTC-4 acoz...@google.com wrote:
>>>
 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  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 acoz...@google.com 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 

Re: [protobuf] Enumerating a variable's fields and setting them

[J G]

Hi Adam,

OK, but would I need to know the fields in the message ahead of time? That 
is what I am trying to avoid.
The paths of the nested messages are in a table, such as

"healthreport/os/version", 3

So the healthreport variable is allocated, and it contains a component 
called os, which itself contains a field called version.

So I am trying to write a generic enum function, that can descend the 
parent, and guided by the path info, can resolve the value that needs to be 
stored there, but if I am to traverse the entire tree manually, how does 
the reflection API help?
On Tuesday, 22 June 2021 at 14:21:59 UTC-4 acoz...@google.com wrote:

> I think the reason this is getting tricky is because you're trying to 
> traverse the descriptors first and then look at the message tree afterward. 
> I would expect it to be much easier if you traverse the message and look at 
> the descriptors at the same time.
>
> On Tue, Jun 22, 2021 at 10:58 AM J G  wrote:
>
>> Hi Adam,
>>
>> That works for the first iteration, but I descend the tree like so: 
>>
>> bool enumpb( const char * pszpath, ENUMPROTOPROC f, const 
>> google::protobuf::Descriptor * d, uintptr_t param ) {
>>
>> std::string path = pszpath;
>>
>> for ( int i = 0; i < d->field_count(); i++ ) {
>>
>> auto field = d->field( i );
>>
>> std::string localpath = pszpath;
>>
>> if ( 0 != strcmp( "component", field->name().c_str() ) ) {
>>
>> localpath.append( field->name() );
>>
>> }
>>
>> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {
>>
>> if ( f && ! f( field, localpath.c_str(), param ) ) {
>>
>> return false;
>>
>> }
>>
>> }
>>
>> auto mt = field->message_type();
>>
>> if ( ! mt ) {
>>
>> continue;
>>
>> } else if ( 0 != strcmp( d->full_name().c_str(), 
>> mt->full_name().c_str() ) ) {
>>
>> std::string localpath2 = localpath;
>>
>> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) 
>> {
>>
>> localpath2.append( "/" );
>>
>> }
>>
>> if ( ! enumpb( hp, report, localpath2.c_str(), f, mt, param ) 
>> ) {
>>
>> return false;
>>
>> }
>>
>> } else {
>>
>> //printf( "Skipping circular %s" EOL, d->full_name().c_str() 
>> );
>>
>> }
>>
>> }
>>
>> return true;
>>
>> }
>>
>> So I start the traversal like this:
>>
>> auto d = report->GetDescriptor();
>>
>> enumpb( "", f, d, param );
>>
>> And it goes down the variable, visiting each leaf and nested child 
>> variable, but I can't address each nested child directly that way, can I?
>> The mt variable does hold the descriptor for each nested variable at some 
>> point, but I don't know how I'd derive the variable's instance from it.
>>
>> On Tuesday, 22 June 2021 at 13:47:15 UTC-4 acoz...@google.com wrote:
>>
>>> 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  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 acoz...@google.com 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  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 

Re: [protobuf] Enumerating a variable's fields and setting them

['Adam Cozzette' via Protocol Buffers]

I think the reason this is getting tricky is because you're trying to
traverse the descriptors first and then look at the message tree afterward.
I would expect it to be much easier if you traverse the message and look at
the descriptors at the same time.

On Tue, Jun 22, 2021 at 10:58 AM J G  wrote:

> Hi Adam,
>
> That works for the first iteration, but I descend the tree like so:
>
> bool enumpb( const char * pszpath, ENUMPROTOPROC f, const
> google::protobuf::Descriptor * d, uintptr_t param ) {
>
> std::string path = pszpath;
>
> for ( int i = 0; i < d->field_count(); i++ ) {
>
> auto field = d->field( i );
>
> std::string localpath = pszpath;
>
> if ( 0 != strcmp( "component", field->name().c_str() ) ) {
>
> localpath.append( field->name() );
>
> }
>
> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {
>
> if ( f && ! f( field, localpath.c_str(), param ) ) {
>
> return false;
>
> }
>
> }
>
> auto mt = field->message_type();
>
> if ( ! mt ) {
>
> continue;
>
> } else if ( 0 != strcmp( d->full_name().c_str(),
> mt->full_name().c_str() ) ) {
>
> std::string localpath2 = localpath;
>
> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {
>
> localpath2.append( "/" );
>
> }
>
> if ( ! enumpb( hp, report, localpath2.c_str(), f, mt, param )
> ) {
>
> return false;
>
> }
>
> } else {
>
> //printf( "Skipping circular %s" EOL, d->full_name().c_str() );
>
> }
>
> }
>
> return true;
>
> }
>
> So I start the traversal like this:
>
> auto d = report->GetDescriptor();
>
> enumpb( "", f, d, param );
>
> And it goes down the variable, visiting each leaf and nested child
> variable, but I can't address each nested child directly that way, can I?
> The mt variable does hold the descriptor for each nested variable at some
> point, but I don't know how I'd derive the variable's instance from it.
>
> On Tuesday, 22 June 2021 at 13:47:15 UTC-4 acoz...@google.com wrote:
>
>> 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  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 acoz...@google.com 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  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 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  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 

Re: [protobuf] Enumerating a variable's fields and setting them

[J G]

Hi Adam,

That works for the first iteration, but I descend the tree like so: 

bool enumpb( const char * pszpath, ENUMPROTOPROC f, const 
google::protobuf::Descriptor * d, uintptr_t param ) {

std::string path = pszpath;

for ( int i = 0; i < d->field_count(); i++ ) {

auto field = d->field( i );

std::string localpath = pszpath;

if ( 0 != strcmp( "component", field->name().c_str() ) ) {

localpath.append( field->name() );

}

if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {

if ( f && ! f( field, localpath.c_str(), param ) ) {

return false;

}

}

auto mt = field->message_type();

if ( ! mt ) {

continue;

} else if ( 0 != strcmp( d->full_name().c_str(), 
mt->full_name().c_str() ) ) {

std::string localpath2 = localpath;

if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {

localpath2.append( "/" );

}

if ( ! enumpb( hp, report, localpath2.c_str(), f, mt, param ) ) 
{

return false;

}

} else {

//printf( "Skipping circular %s" EOL, d->full_name().c_str() );

}

}

return true;

}

So I start the traversal like this:

auto d = report->GetDescriptor();

enumpb( "", f, d, param );

And it goes down the variable, visiting each leaf and nested child 
variable, but I can't address each nested child directly that way, can I?
The mt variable does hold the descriptor for each nested variable at some 
point, but I don't know how I'd derive the variable's instance from it.

On Tuesday, 22 June 2021 at 13:47:15 UTC-4 acoz...@google.com wrote:

> 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  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 acoz...@google.com 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  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 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  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;
>>

Re: [protobuf] Enumerating a variable's fields and setting them

['Adam Cozzette' via Protocol Buffers]

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  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 acoz...@google.com 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  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 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  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 

Re: [protobuf] Enumerating a variable's fields and setting them

[J G]

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 acoz...@google.com 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  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 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  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 
> 

Re: [protobuf] Enumerating a variable's fields and setting them

['Adam Cozzette' via Protocol Buffers]

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  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 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  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
 
 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  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 

Re: [protobuf] Enumerating a variable's fields and setting them

[J G]

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  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 
>>> 
>>>  
>>> 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  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;

Re: [protobuf] Enumerating a variable's fields and setting them

['Adam Cozzette' via Protocol Buffers]

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  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
>> 
>> 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  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 protobuf+u...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com
>>> 
>>> .
>>>
>> --
> 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 protobuf+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/protobuf/7ef6e77e-8635-4b16-b570-b80f75d207d9n%40googlegroups.com
> 

Re: [protobuf] Enumerating a variable's fields and setting them

[J G]

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 
> 
>  
> 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  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 protobuf+u...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com
>>  
>> 
>> .
>>
>

-- 
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 protobuf+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/protobuf/7ef6e77e-8635-4b16-b570-b80f75d207d9n%40googlegroups.com.

Re: [protobuf] Enumerating a variable's fields and setting them

['Adam Cozzette' via Protocol Buffers]

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

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  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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> .
>

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