How can I assign the nested Protobuf messages' values to the main message? C-CodePudding

I'm messing around with Protobuf, trying to get C data over to C# which I then use to use the designated data within Unity. Seeing as Unity makes use of GameObjects like for example a sphere, having both positional data als scaling data, I figured I would try to use this format within the Protobuf message. This leads to the message looking somewhat like this:

syntax = "proto3";

package Sphere;

message Sphere {
    
    message Position {
        float x = 1;
        float y = 2;
        float z = 3;
    }

    message Scale {
        float x = 1;
        float y = 2;
        float z = 3;
    }
}

message Spheres {
    repeated Sphere spheres = 1;
}

Now my question on this is how I can attach the Position and Scale values to a Sphere object within the C file.

As of right now my C file looks like this:

#include <fstream>
#include "sphere.pb.h"

using std::fstream;
Sphere::Sphere sphere1, sphere2;
Sphere::Spheres sphereCollection;

int main() {
    using namespace Sphere;
    std::fstream sphereData("./Assets/Scripts/sphereData.dat", std::ios::binary|std::ios::out);

    Sphere_Position* position1;
    position1->set_x(5);
    position1->set_y(5);
    position1->set_z(5);

    Sphere_Scale* scale1;
    scale1->set_x(5);
    scale1->set_y(5);
    scale1->set_z(5);

    Sphere_Position* position2;
    position2->set_x(5);
    position2->set_y(5);
    position2->set_z(5);

    Sphere_Scale* scale2;
    scale2->set_x(5);
    scale2->set_y(5);
    scale2->set_z(5);


    sphereCollection.add_spheres()->CopyFrom(sphere1);
    sphereCollection.add_spheres()->CopyFrom(sphere2);

    sphereCollection.SerializeToOstream(&sphereData);

    return EXIT_SUCCESS;
}

I figured that there should be some way I could maybe use the CopyFrom function to get the data from the Sphere_Position and Sphere_Scale, I however couldn't find a function that the CopyFrom function could be used on. I did relocate the Position and Scale messages to be contained within the Sphere message and recompiled the C generated classes afterwards, though I don't know if this was a change worth doing.

Please do note my C knowledge ain't all too bright as of yet, same could be said about Protobuf, though I have extensively checked Google's guide about it. (Ofcourse this does not exclude the possibility of me having missed something)

EDIT:

This is the sphere.pb.h:

// Generated by the protocol buffer compiler.  DO NOT EDIT!
// source: sphere.proto

#ifndef PROTOBUF_INCLUDED_sphere_2eproto
#define PROTOBUF_INCLUDED_sphere_2eproto

#include <string>

#include <google/protobuf/stubs/common.h>

#if GOOGLE_PROTOBUF_VERSION < 3006001
#error This file was generated by a newer version of protoc which is
#error incompatible with your Protocol Buffer headers.  Please update
#error your headers.
#endif
#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
#error This file was generated by an older version of protoc which is
#error incompatible with your Protocol Buffer headers.  Please
#error regenerate this file with a newer version of protoc.
#endif

#include <google/protobuf/io/coded_stream.h>
#include <google/protobuf/arena.h>
#include <google/protobuf/arenastring.h>
#include <google/protobuf/generated_message_table_driven.h>
#include <google/protobuf/generated_message_util.h>
#include <google/protobuf/inlined_string_field.h>
#include <google/protobuf/metadata.h>
#include <google/protobuf/message.h>
#include <google/protobuf/repeated_field.h>  // IWYU pragma: export
#include <google/protobuf/extension_set.h>  // IWYU pragma: export
#include <google/protobuf/unknown_field_set.h>
// @@protoc_insertion_point(includes)
#define PROTOBUF_INTERNAL_EXPORT_protobuf_sphere_2eproto 

namespace protobuf_sphere_2eproto {
// Internal implementation detail -- do not use these members.
struct TableStruct {
  static const ::google::protobuf::internal::ParseTableField entries[];
  static const ::google::protobuf::internal::AuxillaryParseTableField aux[];
  static const ::google::protobuf::internal::ParseTable schema[4];
  static const ::google::protobuf::internal::FieldMetadata field_metadata[];
  static const ::google::protobuf::internal::SerializationTable serialization_table[];
  static const ::google::protobuf::uint32 offsets[];
};
void AddDescriptors();
}  // namespace protobuf_sphere_2eproto
namespace Sphere {
class Sphere;
class SphereDefaultTypeInternal;
extern SphereDefaultTypeInternal _Sphere_default_instance_;
class Sphere_Position;
class Sphere_PositionDefaultTypeInternal;
extern Sphere_PositionDefaultTypeInternal _Sphere_Position_default_instance_;
class Sphere_Scale;
class Sphere_ScaleDefaultTypeInternal;
extern Sphere_ScaleDefaultTypeInternal _Sphere_Scale_default_instance_;
class Spheres;
class SpheresDefaultTypeInternal;
extern SpheresDefaultTypeInternal _Spheres_default_instance_;
}  // namespace Sphere
namespace google {
namespace protobuf {
template<> ::Sphere::Sphere* Arena::CreateMaybeMessage<::Sphere::Sphere>(Arena*);
template<> ::Sphere::Sphere_Position* Arena::CreateMaybeMessage<::Sphere::Sphere_Position>(Arena*);
template<> ::Sphere::Sphere_Scale* Arena::CreateMaybeMessage<::Sphere::Sphere_Scale>(Arena*);
template<> ::Sphere::Spheres* Arena::CreateMaybeMessage<::Sphere::Spheres>(Arena*);
}  // namespace protobuf
}  // namespace google
namespace Sphere {

// ===================================================================

class Sphere_Position : public ::google::protobuf::Message /* @@protoc_insertion_point(class_definition:Sphere.Sphere.Position) */ {
 public:
  Sphere_Position();
  virtual ~Sphere_Position();

  Sphere_Position(const Sphere_Position& from);

  inline Sphere_Position& operator=(const Sphere_Position& from) {
    CopyFrom(from);
    return *this;
  }
  #if LANG_CXX11
  Sphere_Position(Sphere_Position&& from) noexcept
    : Sphere_Position() {
    *this = ::std::move(from);
  }

  inline Sphere_Position& operator=(Sphere_Position&& from) noexcept {
    if (GetArenaNoVirtual() == from.GetArenaNoVirtual()) {
      if (this != &from) InternalSwap(&from);
    } else {
      CopyFrom(from);
    }
    return *this;
  }
  #endif
  static const ::google::protobuf::Descriptor* descriptor();
  static const Sphere_Position& default_instance();

  static void InitAsDefaultInstance();  // FOR INTERNAL USE ONLY
  static inline const Sphere_Position* internal_default_instance() {
    return reinterpret_cast<const Sphere_Position*>(
               &_Sphere_Position_default_instance_);
  }
  static constexpr int kIndexInFileMessages =
    0;

  void Swap(Sphere_Position* other);
  friend void swap(Sphere_Position& a, Sphere_Position& b) {
    a.Swap(&b);
  }

  // implements Message ----------------------------------------------

  inline Sphere_Position* New() const final {
    return CreateMaybeMessage<Sphere_Position>(NULL);
  }

  Sphere_Position* New(::google::protobuf::Arena* arena) const final {
    return CreateMaybeMessage<Sphere_Position>(arena);
  }
  void CopyFrom(const ::google::protobuf::Message& from) final;
  void MergeFrom(const ::google::protobuf::Message& from) final;
  void CopyFrom(const Sphere_Position& from);
  void MergeFrom(const Sphere_Position& from);
  void Clear() final;
  bool IsInitialized() const final;

  size_t ByteSizeLong() const final;
  bool MergePartialFromCodedStream(
      ::google::protobuf::io::CodedInputStream* input) final;
  void SerializeWithCachedSizes(
      ::google::protobuf::io::CodedOutputStream* output) const final;
  ::google::protobuf::uint8* InternalSerializeWithCachedSizesToArray(
      bool deterministic, ::google::protobuf::uint8* target) const final;
  int GetCachedSize() const final { return _cached_size_.Get(); }

  private:
  void SharedCtor();
  void SharedDtor();
  void SetCachedSize(int size) const final;
  void InternalSwap(Sphere_Position* other);
  private:
  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
    return NULL;
  }
  inline void* MaybeArenaPtr() const {
    return NULL;
  }
  public:

  ::google::protobuf::Metadata GetMetadata() const final;

  // nested types ----------------------------------------------------

  // accessors -------------------------------------------------------

  // float x = 1;
  void clear_x();
  static const int kXFieldNumber = 1;
  float x() const;
  void set_x(float value);

  // float y = 2;
  void clear_y();
  static const int kYFieldNumber = 2;
  float y() const;
  void set_y(float value);

  // float z = 3;
  void clear_z();
  static const int kZFieldNumber = 3;
  float z() const;
  void set_z(float value);

  // @@protoc_insertion_point(class_scope:Sphere.Sphere.Position)
 private:

  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
  float x_;
  float y_;
  float z_;
  mutable ::google::protobuf::internal::CachedSize _cached_size_;
  friend struct ::protobuf_sphere_2eproto::TableStruct;
};
// -------------------------------------------------------------------

class Sphere_Scale : public ::google::protobuf::Message /* @@protoc_insertion_point(class_definition:Sphere.Sphere.Scale) */ {
 public:
  Sphere_Scale();
  virtual ~Sphere_Scale();

  Sphere_Scale(const Sphere_Scale& from);

  inline Sphere_Scale& operator=(const Sphere_Scale& from) {
    CopyFrom(from);
    return *this;
  }
  #if LANG_CXX11
  Sphere_Scale(Sphere_Scale&& from) noexcept
    : Sphere_Scale() {
    *this = ::std::move(from);
  }

  inline Sphere_Scale& operator=(Sphere_Scale&& from) noexcept {
    if (GetArenaNoVirtual() == from.GetArenaNoVirtual()) {
      if (this != &from) InternalSwap(&from);
    } else {
      CopyFrom(from);
    }
    return *this;
  }
  #endif
  static const ::google::protobuf::Descriptor* descriptor();
  static const Sphere_Scale& default_instance();

  static void InitAsDefaultInstance();  // FOR INTERNAL USE ONLY
  static inline const Sphere_Scale* internal_default_instance() {
    return reinterpret_cast<const Sphere_Scale*>(
               &_Sphere_Scale_default_instance_);
  }
  static constexpr int kIndexInFileMessages =
    1;

  void Swap(Sphere_Scale* other);
  friend void swap(Sphere_Scale& a, Sphere_Scale& b) {
    a.Swap(&b);
  }

  // implements Message ----------------------------------------------

  inline Sphere_Scale* New() const final {
    return CreateMaybeMessage<Sphere_Scale>(NULL);
  }

  Sphere_Scale* New(::google::protobuf::Arena* arena) const final {
    return CreateMaybeMessage<Sphere_Scale>(arena);
  }
  void CopyFrom(const ::google::protobuf::Message& from) final;
  void MergeFrom(const ::google::protobuf::Message& from) final;
  void CopyFrom(const Sphere_Scale& from);
  void MergeFrom(const Sphere_Scale& from);
  void Clear() final;
  bool IsInitialized() const final;

  size_t ByteSizeLong() const final;
  bool MergePartialFromCodedStream(
      ::google::protobuf::io::CodedInputStream* input) final;
  void SerializeWithCachedSizes(
      ::google::protobuf::io::CodedOutputStream* output) const final;
  ::google::protobuf::uint8* InternalSerializeWithCachedSizesToArray(
      bool deterministic, ::google::protobuf::uint8* target) const final;
  int GetCachedSize() const final { return _cached_size_.Get(); }

  private:
  void SharedCtor();
  void SharedDtor();
  void SetCachedSize(int size) const final;
  void InternalSwap(Sphere_Scale* other);
  private:
  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
    return NULL;
  }
  inline void* MaybeArenaPtr() const {
    return NULL;
  }
  public:

  ::google::protobuf::Metadata GetMetadata() const final;

  // nested types ----------------------------------------------------

  // accessors -------------------------------------------------------

  // float x = 1;
  void clear_x();
  static const int kXFieldNumber = 1;
  float x() const;
  void set_x(float value);

  // float y = 2;
  void clear_y();
  static const int kYFieldNumber = 2;
  float y() const;
  void set_y(float value);

  // float z = 3;
  void clear_z();
  static const int kZFieldNumber = 3;
  float z() const;
  void set_z(float value);

  // @@protoc_insertion_point(class_scope:Sphere.Sphere.Scale)
 private:

  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
  float x_;
  float y_;
  float z_;
  mutable ::google::protobuf::internal::CachedSize _cached_size_;
  friend struct ::protobuf_sphere_2eproto::TableStruct;
};
// -------------------------------------------------------------------

class Sphere : public ::google::protobuf::Message /* @@protoc_insertion_point(class_definition:Sphere.Sphere) */ {
 public:
  Sphere();
  virtual ~Sphere();

  Sphere(const Sphere& from);

  inline Sphere& operator=(const Sphere& from) {
    CopyFrom(from);
    return *this;
  }
  #if LANG_CXX11
  Sphere(Sphere&& from) noexcept
    : Sphere() {
    *this = ::std::move(from);
  }

  inline Sphere& operator=(Sphere&& from) noexcept {
    if (GetArenaNoVirtual() == from.GetArenaNoVirtual()) {
      if (this != &from) InternalSwap(&from);
    } else {
      CopyFrom(from);
    }
    return *this;
  }
  #endif
  static const ::google::protobuf::Descriptor* descriptor();
  static const Sphere& default_instance();

  static void InitAsDefaultInstance();  // FOR INTERNAL USE ONLY
  static inline const Sphere* internal_default_instance() {
    return reinterpret_cast<const Sphere*>(
               &_Sphere_default_instance_);
  }
  static constexpr int kIndexInFileMessages =
    2;

  void Swap(Sphere* other);
  friend void swap(Sphere& a, Sphere& b) {
    a.Swap(&b);
  }

  // implements Message ----------------------------------------------

  inline Sphere* New() const final {
    return CreateMaybeMessage<Sphere>(NULL);
  }

  Sphere* New(::google::protobuf::Arena* arena) const final {
    return CreateMaybeMessage<Sphere>(arena);
  }
  void CopyFrom(const ::google::protobuf::Message& from) final;
  void MergeFrom(const ::google::protobuf::Message& from) final;
  void CopyFrom(const Sphere& from);
  void MergeFrom(const Sphere& from);
  void Clear() final;
  bool IsInitialized() const final;

  size_t ByteSizeLong() const final;
  bool MergePartialFromCodedStream(
      ::google::protobuf::io::CodedInputStream* input) final;
  void SerializeWithCachedSizes(
      ::google::protobuf::io::CodedOutputStream* output) const final;
  ::google::protobuf::uint8* InternalSerializeWithCachedSizesToArray(
      bool deterministic, ::google::protobuf::uint8* target) const final;
  int GetCachedSize() const final { return _cached_size_.Get(); }

  private:
  void SharedCtor();
  void SharedDtor();
  void SetCachedSize(int size) const final;
  void InternalSwap(Sphere* other);
  private:
  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
    return NULL;
  }
  inline void* MaybeArenaPtr() const {
    return NULL;
  }
  public:

  ::google::protobuf::Metadata GetMetadata() const final;

  // nested types ----------------------------------------------------

  typedef Sphere_Position Position;
  typedef Sphere_Scale Scale;

  // accessors -------------------------------------------------------

  // @@protoc_insertion_point(class_scope:Sphere.Sphere)
 private:

  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
  mutable ::google::protobuf::internal::CachedSize _cached_size_;
  friend struct ::protobuf_sphere_2eproto::TableStruct;
};
// -------------------------------------------------------------------

class Spheres : public ::google::protobuf::Message /* @@protoc_insertion_point(class_definition:Sphere.Spheres) */ {
 public:
  Spheres();
  virtual ~Spheres();

  Spheres(const Spheres& from);

  inline Spheres& operator=(const Spheres& from) {
    CopyFrom(from);
    return *this;
  }
  #if LANG_CXX11
  Spheres(Spheres&& from) noexcept
    : Spheres() {
    *this = ::std::move(from);
  }

  inline Spheres& operator=(Spheres&& from) noexcept {
    if (GetArenaNoVirtual() == from.GetArenaNoVirtual()) {
      if (this != &from) InternalSwap(&from);
    } else {
      CopyFrom(from);
    }
    return *this;
  }
  #endif
  static const ::google::protobuf::Descriptor* descriptor();
  static const Spheres& default_instance();

  static void InitAsDefaultInstance();  // FOR INTERNAL USE ONLY
  static inline const Spheres* internal_default_instance() {
    return reinterpret_cast<const Spheres*>(
               &_Spheres_default_instance_);
  }
  static constexpr int kIndexInFileMessages =
    3;

  void Swap(Spheres* other);
  friend void swap(Spheres& a, Spheres& b) {
    a.Swap(&b);
  }

  // implements Message ----------------------------------------------

  inline Spheres* New() const final {
    return CreateMaybeMessage<Spheres>(NULL);
  }

  Spheres* New(::google::protobuf::Arena* arena) const final {
    return CreateMaybeMessage<Spheres>(arena);
  }
  void CopyFrom(const ::google::protobuf::Message& from) final;
  void MergeFrom(const ::google::protobuf::Message& from) final;
  void CopyFrom(const Spheres& from);
  void MergeFrom(const Spheres& from);
  void Clear() final;
  bool IsInitialized() const final;

  size_t ByteSizeLong() const final;
  bool MergePartialFromCodedStream(
      ::google::protobuf::io::CodedInputStream* input) final;
  void SerializeWithCachedSizes(
      ::google::protobuf::io::CodedOutputStream* output) const final;
  ::google::protobuf::uint8* InternalSerializeWithCachedSizesToArray(
      bool deterministic, ::google::protobuf::uint8* target) const final;
  int GetCachedSize() const final { return _cached_size_.Get(); }

  private:
  void SharedCtor();
  void SharedDtor();
  void SetCachedSize(int size) const final;
  void InternalSwap(Spheres* other);
  private:
  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
    return NULL;
  }
  inline void* MaybeArenaPtr() const {
    return NULL;
  }
  public:

  ::google::protobuf::Metadata GetMetadata() const final;

  // nested types ----------------------------------------------------

  // accessors -------------------------------------------------------

  // repeated .Sphere.Sphere spheres = 1;
  int spheres_size() const;
  void clear_spheres();
  static const int kSpheresFieldNumber = 1;
  ::Sphere::Sphere* mutable_spheres(int index);
  ::google::protobuf::RepeatedPtrField< ::Sphere::Sphere >*
      mutable_spheres();
  const ::Sphere::Sphere& spheres(int index) const;
  ::Sphere::Sphere* add_spheres();
  const ::google::protobuf::RepeatedPtrField< ::Sphere::Sphere >&
      spheres() const;

  // @@protoc_insertion_point(class_scope:Sphere.Spheres)
 private:

  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
  ::google::protobuf::RepeatedPtrField< ::Sphere::Sphere > spheres_;
  mutable ::google::protobuf::internal::CachedSize _cached_size_;
  friend struct ::protobuf_sphere_2eproto::TableStruct;
};
// ===================================================================


// ===================================================================

#ifdef __GNUC__
  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wstrict-aliasing"
#endif  // __GNUC__
// Sphere_Position

// float x = 1;
inline void Sphere_Position::clear_x() {
  x_ = 0;
}
inline float Sphere_Position::x() const {
  // @@protoc_insertion_point(field_get:Sphere.Sphere.Position.x)
  return x_;
}
inline void Sphere_Position::set_x(float value) {
  
  x_ = value;
  // @@protoc_insertion_point(field_set:Sphere.Sphere.Position.x)
}

// float y = 2;
inline void Sphere_Position::clear_y() {
  y_ = 0;
}
inline float Sphere_Position::y() const {
  // @@protoc_insertion_point(field_get:Sphere.Sphere.Position.y)
  return y_;
}
inline void Sphere_Position::set_y(float value) {
  
  y_ = value;
  // @@protoc_insertion_point(field_set:Sphere.Sphere.Position.y)
}

// float z = 3;
inline void Sphere_Position::clear_z() {
  z_ = 0;
}
inline float Sphere_Position::z() const {
  // @@protoc_insertion_point(field_get:Sphere.Sphere.Position.z)
  return z_;
}
inline void Sphere_Position::set_z(float value) {
  
  z_ = value;
  // @@protoc_insertion_point(field_set:Sphere.Sphere.Position.z)
}

// -------------------------------------------------------------------

// Sphere_Scale

// float x = 1;
inline void Sphere_Scale::clear_x() {
  x_ = 0;
}
inline float Sphere_Scale::x() const {
  // @@protoc_insertion_point(field_get:Sphere.Sphere.Scale.x)
  return x_;
}
inline void Sphere_Scale::set_x(float value) {
  
  x_ = value;
  // @@protoc_insertion_point(field_set:Sphere.Sphere.Scale.x)
}

// float y = 2;
inline void Sphere_Scale::clear_y() {
  y_ = 0;
}
inline float Sphere_Scale::y() const {
  // @@protoc_insertion_point(field_get:Sphere.Sphere.Scale.y)
  return y_;
}
inline void Sphere_Scale::set_y(float value) {
  
  y_ = value;
  // @@protoc_insertion_point(field_set:Sphere.Sphere.Scale.y)
}

// float z = 3;
inline void Sphere_Scale::clear_z() {
  z_ = 0;
}
inline float Sphere_Scale::z() const {
  // @@protoc_insertion_point(field_get:Sphere.Sphere.Scale.z)
  return z_;
}
inline void Sphere_Scale::set_z(float value) {
  
  z_ = value;
  // @@protoc_insertion_point(field_set:Sphere.Sphere.Scale.z)
}

// -------------------------------------------------------------------

// Sphere

// -------------------------------------------------------------------

// Spheres

// repeated .Sphere.Sphere spheres = 1;
inline int Spheres::spheres_size() const {
  return spheres_.size();
}
inline void Spheres::clear_spheres() {
  spheres_.Clear();
}
inline ::Sphere::Sphere* Spheres::mutable_spheres(int index) {
  // @@protoc_insertion_point(field_mutable:Sphere.Spheres.spheres)
  return spheres_.Mutable(index);
}
inline ::google::protobuf::RepeatedPtrField< ::Sphere::Sphere >*
Spheres::mutable_spheres() {
  // @@protoc_insertion_point(field_mutable_list:Sphere.Spheres.spheres)
  return &spheres_;
}
inline const ::Sphere::Sphere& Spheres::spheres(int index) const {
  // @@protoc_insertion_point(field_get:Sphere.Spheres.spheres)
  return spheres_.Get(index);
}
inline ::Sphere::Sphere* Spheres::add_spheres() {
  // @@protoc_insertion_point(field_add:Sphere.Spheres.spheres)
  return spheres_.Add();
}
inline const ::google::protobuf::RepeatedPtrField< ::Sphere::Sphere >&
Spheres::spheres() const {
  // @@protoc_insertion_point(field_list:Sphere.Spheres.spheres)
  return spheres_;
}

#ifdef __GNUC__
  #pragma GCC diagnostic pop
#endif  // __GNUC__
// -------------------------------------------------------------------

// -------------------------------------------------------------------

// -------------------------------------------------------------------


// @@protoc_insertion_point(namespace_scope)

}  // namespace Sphere

// @@protoc_insertion_point(global_scope)

#endif  // PROTOBUF_INCLUDED_sphere_2eproto

CodePudding user response：

First, in addition to declaring your nested types, you also need to add fields to your message

message Sphere {
    
    message Position {
        float x = 1;
        float y = 2;
        float z = 3;
    }
    Position position = 1;

    message Scale {
        float x = 1;
        float y = 2;
        float z = 3;
    }
    Scale scale = 2;
}

then I would refactor how you create and populate the nested fields to something like

auto sphere1 = sphereCollection.add_spheres();
sphere1->mutable_position()->set_x(5);
sphere1->mutable_position()->set_y(5);
sphere1->mutable_position()->set_z(5);
sphere1->mutable_scale()->set_x(5);
sphere1->mutable_scale()->set_y(5);
sphere1->mutable_scale()->set_z(5);

auto sphere2 = sphereCollection.add_spheres();
sphere2->mutable_position()->set_x(5);
sphere2->mutable_position()->set_y(5);
sphere2->mutable_position()->set_z(5);
sphere2->mutable_scale()->set_x(5);
sphere2->mutable_scale()->set_y(5);
sphere2->mutable_scale()->set_z(5);

where you can use add_* to allocate a nested repeated object from the current object and get a pointer back, and similarly mutable_* for the desired field.