test.cpp

#include <google/protobuf/util/json_util.h>

#include <iostream>

#include "test.pb.h"

int main(int argc, char** argv) {
    auto t = test::Simple{};

    t.set_testint(4);
    t.set_teststring("foobar");

    std::string result;
    google::protobuf::util::MessageToJsonString(t, &result, google::protobuf::util::JsonPrintOptions());

    std::cout << result << std::endl;

    return 0;
}

test.pb.cc

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

#define INTERNAL_SUPPRESS_PROTOBUF_FIELD_DEPRECATION
#include "test.pb.h"

#include <algorithm>

#include <google/protobuf/stubs/common.h>
#include <google/protobuf/stubs/port.h>
#include <google/protobuf/stubs/once.h>
#include <google/protobuf/io/coded_stream.h>
#include <google/protobuf/wire_format_lite_inl.h>
#include <google/protobuf/descriptor.h>
#include <google/protobuf/generated_message_reflection.h>
#include <google/protobuf/reflection_ops.h>
#include <google/protobuf/wire_format.h>
// @@protoc_insertion_point(includes)

namespace test {

namespace {

const ::google::protobuf::Descriptor* Simple_descriptor_ = NULL;
const ::google::protobuf::internal::GeneratedMessageReflection*
  Simple_reflection_ = NULL;

}  // namespace


void protobuf_AssignDesc_test_2eproto() {
  protobuf_AddDesc_test_2eproto();
  const ::google::protobuf::FileDescriptor* file =
    ::google::protobuf::DescriptorPool::generated_pool()->FindFileByName(
      "test.proto");
  GOOGLE_CHECK(file != NULL);
  Simple_descriptor_ = file->message_type(0);
  static const int Simple_offsets_[2] = {
    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(Simple, testint_),
    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(Simple, teststring_),
  };
  Simple_reflection_ =
    ::google::protobuf::internal::GeneratedMessageReflection::NewGeneratedMessageReflection(
      Simple_descriptor_,
      Simple::default_instance_,
      Simple_offsets_,
      -1,
      -1,
      -1,
      sizeof(Simple),
      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(Simple, _internal_metadata_),
      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(Simple, _is_default_instance_));
}

namespace {

GOOGLE_PROTOBUF_DECLARE_ONCE(protobuf_AssignDescriptors_once_);
inline void protobuf_AssignDescriptorsOnce() {
  ::google::protobuf::GoogleOnceInit(&protobuf_AssignDescriptors_once_,
                 &protobuf_AssignDesc_test_2eproto);
}

void protobuf_RegisterTypes(const ::std::string&) {
  protobuf_AssignDescriptorsOnce();
  ::google::protobuf::MessageFactory::InternalRegisterGeneratedMessage(
      Simple_descriptor_, &Simple::default_instance());
}

}  // namespace

void protobuf_ShutdownFile_test_2eproto() {
  delete Simple::default_instance_;
  delete Simple_reflection_;
}

void protobuf_AddDesc_test_2eproto() {
  static bool already_here = false;
  if (already_here) return;
  already_here = true;
  GOOGLE_PROTOBUF_VERIFY_VERSION;

  ::google::protobuf::DescriptorPool::InternalAddGeneratedFile(
    "\n\ntest.proto\022\004test\"-\n\006Simple\022\017\n\007testInt\030"
    "\001 \001(\003\022\022\n\ntestString\030\002 \001(\tb\006proto3", 73);
  ::google::protobuf::MessageFactory::InternalRegisterGeneratedFile(
    "test.proto", &protobuf_RegisterTypes);
  Simple::default_instance_ = new Simple();
  Simple::default_instance_->InitAsDefaultInstance();
  ::google::protobuf::internal::OnShutdown(&protobuf_ShutdownFile_test_2eproto);
}

// Force AddDescriptors() to be called at static initialization time.
struct StaticDescriptorInitializer_test_2eproto {
  StaticDescriptorInitializer_test_2eproto() {
    protobuf_AddDesc_test_2eproto();
  }
} static_descriptor_initializer_test_2eproto_;

namespace {

static void MergeFromFail(int line) GOOGLE_ATTRIBUTE_COLD;
static void MergeFromFail(int line) {
  GOOGLE_CHECK(false) << __FILE__ << ":" << line;
}

}  // namespace


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

#if !defined(_MSC_VER) || _MSC_VER >= 1900
const int Simple::kTestIntFieldNumber;
const int Simple::kTestStringFieldNumber;
#endif  // !defined(_MSC_VER) || _MSC_VER >= 1900

Simple::Simple()
  : ::google::protobuf::Message(), _internal_metadata_(NULL) {
  SharedCtor();
  // @@protoc_insertion_point(constructor:test.Simple)
}

void Simple::InitAsDefaultInstance() {
  _is_default_instance_ = true;
}

Simple::Simple(const Simple& from)
  : ::google::protobuf::Message(),
    _internal_metadata_(NULL) {
  SharedCtor();
  MergeFrom(from);
  // @@protoc_insertion_point(copy_constructor:test.Simple)
}

void Simple::SharedCtor() {
    _is_default_instance_ = false;
  ::google::protobuf::internal::GetEmptyString();
  _cached_size_ = 0;
  testint_ = GOOGLE_LONGLONG(0);
  teststring_.UnsafeSetDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}

Simple::~Simple() {
  // @@protoc_insertion_point(destructor:test.Simple)
  SharedDtor();
}

void Simple::SharedDtor() {
  teststring_.DestroyNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
  if (this != default_instance_) {
  }
}

void Simple::SetCachedSize(int size) const {
  GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();
  _cached_size_ = size;
  GOOGLE_SAFE_CONCURRENT_WRITES_END();
}
const ::google::protobuf::Descriptor* Simple::descriptor() {
  protobuf_AssignDescriptorsOnce();
  return Simple_descriptor_;
}

const Simple& Simple::default_instance() {
  if (default_instance_ == NULL) protobuf_AddDesc_test_2eproto();
  return *default_instance_;
}

Simple* Simple::default_instance_ = NULL;

Simple* Simple::New(::google::protobuf::Arena* arena) const {
  Simple* n = new Simple;
  if (arena != NULL) {
    arena->Own(n);
  }
  return n;
}

void Simple::Clear() {
// @@protoc_insertion_point(message_clear_start:test.Simple)
  testint_ = GOOGLE_LONGLONG(0);
  teststring_.ClearToEmptyNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}

bool Simple::MergePartialFromCodedStream(
    ::google::protobuf::io::CodedInputStream* input) {
#define DO_(EXPRESSION) if (!GOOGLE_PREDICT_TRUE(EXPRESSION)) goto failure
  ::google::protobuf::uint32 tag;
  // @@protoc_insertion_point(parse_start:test.Simple)
  for (;;) {
    ::std::pair< ::google::protobuf::uint32, bool> p = input->ReadTagWithCutoff(127);
    tag = p.first;
    if (!p.second) goto handle_unusual;
    switch (::google::protobuf::internal::WireFormatLite::GetTagFieldNumber(tag)) {
      // optional int64 testInt = 1;
      case 1: {
        if (tag == 8) {
          DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<
                   ::google::protobuf::int64, ::google::protobuf::internal::WireFormatLite::TYPE_INT64>(
                 input, &testint_)));

        } else {
          goto handle_unusual;
        }
        if (input->ExpectTag(18)) goto parse_testString;
        break;
      }

      // optional string testString = 2;
      case 2: {
        if (tag == 18) {
         parse_testString:
          DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                input, this->mutable_teststring()));
          DO_(::google::protobuf::internal::WireFormatLite::VerifyUtf8String(
            this->teststring().data(), this->teststring().length(),
            ::google::protobuf::internal::WireFormatLite::PARSE,
            "test.Simple.testString"));
        } else {
          goto handle_unusual;
        }
        if (input->ExpectAtEnd()) goto success;
        break;
      }

      default: {
      handle_unusual:
        if (tag == 0 ||
            ::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
            ::google::protobuf::internal::WireFormatLite::WIRETYPE_END_GROUP) {
          goto success;
        }
        DO_(::google::protobuf::internal::WireFormatLite::SkipField(input, tag));
        break;
      }
    }
  }
success:
  // @@protoc_insertion_point(parse_success:test.Simple)
  return true;
failure:
  // @@protoc_insertion_point(parse_failure:test.Simple)
  return false;
#undef DO_
}

void Simple::SerializeWithCachedSizes(
    ::google::protobuf::io::CodedOutputStream* output) const {
  // @@protoc_insertion_point(serialize_start:test.Simple)
  // optional int64 testInt = 1;
  if (this->testint() != 0) {
    ::google::protobuf::internal::WireFormatLite::WriteInt64(1, this->testint(), output);
  }

  // optional string testString = 2;
  if (this->teststring().size() > 0) {
    ::google::protobuf::internal::WireFormatLite::VerifyUtf8String(
      this->teststring().data(), this->teststring().length(),
      ::google::protobuf::internal::WireFormatLite::SERIALIZE,
      "test.Simple.testString");
    ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
      2, this->teststring(), output);
  }

  // @@protoc_insertion_point(serialize_end:test.Simple)
}

::google::protobuf::uint8* Simple::SerializeWithCachedSizesToArray(
    ::google::protobuf::uint8* target) const {
  // @@protoc_insertion_point(serialize_to_array_start:test.Simple)
  // optional int64 testInt = 1;
  if (this->testint() != 0) {
    target = ::google::protobuf::internal::WireFormatLite::WriteInt64ToArray(1, this->testint(), target);
  }

  // optional string testString = 2;
  if (this->teststring().size() > 0) {
    ::google::protobuf::internal::WireFormatLite::VerifyUtf8String(
      this->teststring().data(), this->teststring().length(),
      ::google::protobuf::internal::WireFormatLite::SERIALIZE,
      "test.Simple.testString");
    target =
      ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
        2, this->teststring(), target);
  }

  // @@protoc_insertion_point(serialize_to_array_end:test.Simple)
  return target;
}

int Simple::ByteSize() const {
// @@protoc_insertion_point(message_byte_size_start:test.Simple)
  int total_size = 0;

  // optional int64 testInt = 1;
  if (this->testint() != 0) {
    total_size += 1 +
      ::google::protobuf::internal::WireFormatLite::Int64Size(
        this->testint());
  }

  // optional string testString = 2;
  if (this->teststring().size() > 0) {
    total_size += 1 +
      ::google::protobuf::internal::WireFormatLite::StringSize(
        this->teststring());
  }

  GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();
  _cached_size_ = total_size;
  GOOGLE_SAFE_CONCURRENT_WRITES_END();
  return total_size;
}

void Simple::MergeFrom(const ::google::protobuf::Message& from) {
// @@protoc_insertion_point(generalized_merge_from_start:test.Simple)
  if (GOOGLE_PREDICT_FALSE(&from == this)) MergeFromFail(__LINE__);
  const Simple* source = 
      ::google::protobuf::internal::DynamicCastToGenerated<const Simple>(
          &from);
  if (source == NULL) {
  // @@protoc_insertion_point(generalized_merge_from_cast_fail:test.Simple)
    ::google::protobuf::internal::ReflectionOps::Merge(from, this);
  } else {
  // @@protoc_insertion_point(generalized_merge_from_cast_success:test.Simple)
    MergeFrom(*source);
  }
}

void Simple::MergeFrom(const Simple& from) {
// @@protoc_insertion_point(class_specific_merge_from_start:test.Simple)
  if (GOOGLE_PREDICT_FALSE(&from == this)) MergeFromFail(__LINE__);
  if (from.testint() != 0) {
    set_testint(from.testint());
  }
  if (from.teststring().size() > 0) {

    teststring_.AssignWithDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), from.teststring_);
  }
}

void Simple::CopyFrom(const ::google::protobuf::Message& from) {
// @@protoc_insertion_point(generalized_copy_from_start:test.Simple)
  if (&from == this) return;
  Clear();
  MergeFrom(from);
}

void Simple::CopyFrom(const Simple& from) {
// @@protoc_insertion_point(class_specific_copy_from_start:test.Simple)
  if (&from == this) return;
  Clear();
  MergeFrom(from);
}

bool Simple::IsInitialized() const {

  return true;
}

void Simple::Swap(Simple* other) {
  if (other == this) return;
  InternalSwap(other);
}
void Simple::InternalSwap(Simple* other) {
  std::swap(testint_, other->testint_);
  teststring_.Swap(&other->teststring_);
  _internal_metadata_.Swap(&other->_internal_metadata_);
  std::swap(_cached_size_, other->_cached_size_);
}

::google::protobuf::Metadata Simple::GetMetadata() const {
  protobuf_AssignDescriptorsOnce();
  ::google::protobuf::Metadata metadata;
  metadata.descriptor = Simple_descriptor_;
  metadata.reflection = Simple_reflection_;
  return metadata;
}

#if PROTOBUF_INLINE_NOT_IN_HEADERS
// Simple

// optional int64 testInt = 1;
void Simple::clear_testint() {
  testint_ = GOOGLE_LONGLONG(0);
}
 ::google::protobuf::int64 Simple::testint() const {
  // @@protoc_insertion_point(field_get:test.Simple.testInt)
  return testint_;
}
 void Simple::set_testint(::google::protobuf::int64 value) {
  
  testint_ = value;
  // @@protoc_insertion_point(field_set:test.Simple.testInt)
}

// optional string testString = 2;
void Simple::clear_teststring() {
  teststring_.ClearToEmptyNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
 const ::std::string& Simple::teststring() const {
  // @@protoc_insertion_point(field_get:test.Simple.testString)
  return teststring_.GetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
 void Simple::set_teststring(const ::std::string& value) {
  
  teststring_.SetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value);
  // @@protoc_insertion_point(field_set:test.Simple.testString)
}
 void Simple::set_teststring(const char* value) {
  
  teststring_.SetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value));
  // @@protoc_insertion_point(field_set_char:test.Simple.testString)
}
 void Simple::set_teststring(const char* value, size_t size) {
  
  teststring_.SetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
      ::std::string(reinterpret_cast<const char*>(value), size));
  // @@protoc_insertion_point(field_set_pointer:test.Simple.testString)
}
 ::std::string* Simple::mutable_teststring() {
  
  // @@protoc_insertion_point(field_mutable:test.Simple.testString)
  return teststring_.MutableNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
 ::std::string* Simple::release_teststring() {
  // @@protoc_insertion_point(field_release:test.Simple.testString)
  
  return teststring_.ReleaseNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
 void Simple::set_allocated_teststring(::std::string* teststring) {
  if (teststring != NULL) {
    
  } else {
    
  }
  teststring_.SetAllocatedNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), teststring);
  // @@protoc_insertion_point(field_set_allocated:test.Simple.testString)
}

#endif  // PROTOBUF_INLINE_NOT_IN_HEADERS

// @@protoc_insertion_point(namespace_scope)

}  // namespace test

// @@protoc_insertion_point(global_scope)

test.pb.h

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

#ifndef PROTOBUF_test_2eproto__INCLUDED
#define PROTOBUF_test_2eproto__INCLUDED

#include <string>

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

#if GOOGLE_PROTOBUF_VERSION < 3000000
#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 3000000 < 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/arena.h>
#include <google/protobuf/arenastring.h>
#include <google/protobuf/generated_message_util.h>
#include <google/protobuf/metadata.h>
#include <google/protobuf/message.h>
#include <google/protobuf/repeated_field.h>
#include <google/protobuf/extension_set.h>
#include <google/protobuf/unknown_field_set.h>
// @@protoc_insertion_point(includes)

namespace test {

// Internal implementation detail -- do not call these.
void protobuf_AddDesc_test_2eproto();
void protobuf_AssignDesc_test_2eproto();
void protobuf_ShutdownFile_test_2eproto();

class Simple;

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

class Simple : public ::google::protobuf::Message {
 public:
  Simple();
  virtual ~Simple();

  Simple(const Simple& from);

  inline Simple& operator=(const Simple& from) {
    CopyFrom(from);
    return *this;
  }

  static const ::google::protobuf::Descriptor* descriptor();
  static const Simple& default_instance();

  void Swap(Simple* other);

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

  inline Simple* New() const { return New(NULL); }

  Simple* New(::google::protobuf::Arena* arena) const;
  void CopyFrom(const ::google::protobuf::Message& from);
  void MergeFrom(const ::google::protobuf::Message& from);
  void CopyFrom(const Simple& from);
  void MergeFrom(const Simple& from);
  void Clear();
  bool IsInitialized() const;

  int ByteSize() const;
  bool MergePartialFromCodedStream(
      ::google::protobuf::io::CodedInputStream* input);
  void SerializeWithCachedSizes(
      ::google::protobuf::io::CodedOutputStream* output) const;
  ::google::protobuf::uint8* SerializeWithCachedSizesToArray(::google::protobuf::uint8* output) const;
  int GetCachedSize() const { return _cached_size_; }
  private:
  void SharedCtor();
  void SharedDtor();
  void SetCachedSize(int size) const;
  void InternalSwap(Simple* other);
  private:
  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
    return _internal_metadata_.arena();
  }
  inline void* MaybeArenaPtr() const {
    return _internal_metadata_.raw_arena_ptr();
  }
  public:

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

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

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

  // optional int64 testInt = 1;
  void clear_testint();
  static const int kTestIntFieldNumber = 1;
  ::google::protobuf::int64 testint() const;
  void set_testint(::google::protobuf::int64 value);

  // optional string testString = 2;
  void clear_teststring();
  static const int kTestStringFieldNumber = 2;
  const ::std::string& teststring() const;
  void set_teststring(const ::std::string& value);
  void set_teststring(const char* value);
  void set_teststring(const char* value, size_t size);
  ::std::string* mutable_teststring();
  ::std::string* release_teststring();
  void set_allocated_teststring(::std::string* teststring);

  // @@protoc_insertion_point(class_scope:test.Simple)
 private:

  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
  bool _is_default_instance_;
  ::google::protobuf::int64 testint_;
  ::google::protobuf::internal::ArenaStringPtr teststring_;
  mutable int _cached_size_;
  friend void  protobuf_AddDesc_test_2eproto();
  friend void protobuf_AssignDesc_test_2eproto();
  friend void protobuf_ShutdownFile_test_2eproto();

  void InitAsDefaultInstance();
  static Simple* default_instance_;
};
// ===================================================================


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

#if !PROTOBUF_INLINE_NOT_IN_HEADERS
// Simple

// optional int64 testInt = 1;
inline void Simple::clear_testint() {
  testint_ = GOOGLE_LONGLONG(0);
}
inline ::google::protobuf::int64 Simple::testint() const {
  // @@protoc_insertion_point(field_get:test.Simple.testInt)
  return testint_;
}
inline void Simple::set_testint(::google::protobuf::int64 value) {
  
  testint_ = value;
  // @@protoc_insertion_point(field_set:test.Simple.testInt)
}

// optional string testString = 2;
inline void Simple::clear_teststring() {
  teststring_.ClearToEmptyNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
inline const ::std::string& Simple::teststring() const {
  // @@protoc_insertion_point(field_get:test.Simple.testString)
  return teststring_.GetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
inline void Simple::set_teststring(const ::std::string& value) {
  
  teststring_.SetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value);
  // @@protoc_insertion_point(field_set:test.Simple.testString)
}
inline void Simple::set_teststring(const char* value) {
  
  teststring_.SetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value));
  // @@protoc_insertion_point(field_set_char:test.Simple.testString)
}
inline void Simple::set_teststring(const char* value, size_t size) {
  
  teststring_.SetNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
      ::std::string(reinterpret_cast<const char*>(value), size));
  // @@protoc_insertion_point(field_set_pointer:test.Simple.testString)
}
inline ::std::string* Simple::mutable_teststring() {
  
  // @@protoc_insertion_point(field_mutable:test.Simple.testString)
  return teststring_.MutableNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
inline ::std::string* Simple::release_teststring() {
  // @@protoc_insertion_point(field_release:test.Simple.testString)
  
  return teststring_.ReleaseNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
}
inline void Simple::set_allocated_teststring(::std::string* teststring) {
  if (teststring != NULL) {
    
  } else {
    
  }
  teststring_.SetAllocatedNoArena(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), teststring);
  // @@protoc_insertion_point(field_set_allocated:test.Simple.testString)
}

#endif  // !PROTOBUF_INLINE_NOT_IN_HEADERS

// @@protoc_insertion_point(namespace_scope)

}  // namespace test

// @@protoc_insertion_point(global_scope)

#endif  // PROTOBUF_test_2eproto__INCLUDED

test.proto

syntax = "proto3";
package test;

message Simple {
    int64 testInt = 1;
    string testString = 2;
    Inner inner = 3;
}

message Inner {
    int64
}