[Protobuf] 快速上手:安全高效的序列化指南

标题：[Protobuf] (1)快速上手
@水墨不写bug

在这里插入图片描述

文章目录

一、什么是protobuf？
二、protobuf的特点
三、使用protobuf的过程？
- 1、定义消息格式（.proto文件）
- - (1)指定语法版本
  - (2)package 声明符
- 2、使用protoc编译器生成代码
- - （1）当前目录直接编译：
  - （2）指定目录编译
- 3、在业务中引入并使用生成的类
- 4、在网络通信或存储中使用protobuf序列化数据
四、快速上手写一个小需求来熟悉如何编写proto文件？

一、什么是protobuf？

Protocol Buffers（简称 protobuf）是由 Google 开发的一种与语言无关、平台无关、可扩展的序列化数据结构的方法。它用于结构化数据的序列化与反序列化，类似于 XML 或 JSON，但更小、更快、更简单。

二、protobuf的特点

protobuf 可以把数据结构（比如对象或消息）编码成紧凑的二进制格式，之后再还原回原始的数据结构。 这说明protobuf编码是比较安全的，因为二进制无法被直接阅读。

其他重要特点：

跨语言（支持 Java、C++、Python、Go、C#、JavaScript 等多种语言）
二进制格式，高效且体积小
向后兼容和向前兼容性好（适合长期演进的系统）
需要提前定义数据结构（.proto 文件）

减少开发周期和负担
protobuf可以通过protoc编译器来编译proto文件来生成对应的头文件和源文件，内部已经实现了序列化和反序列化的接口。- - - 节省开发时间，避免重复性造轮子

三、使用protobuf的过程？

1、定义消息格式（.proto文件）

(1)指定语法版本

创建**.proto**文件后，首行需要先指定protobuf的语法版本，如果不指定，默认使用proto2。一般我们都使用proto3。 - - - proto3的语法更加简便，支持更多的语言（比如C#）

(2)package 声明符

在proto文件编译之后，如果写了pageage声明，那么cc和h文件内部会被命名空间封装。
如果没有package声明，则cc和h文件的对应类不会被命名空间包裹。

2、使用protoc编译器生成代码

经过1、2两步，后，就可以编写消息的内部数据结构了，假如如下设计(文件名称为 “contact.proto” )：

//首行：语法指定行
syntax = "proto3";

//package 声明符
package contast;

//定义联系人信息
message PersonInfo
{
    string name = 1;
    int32 age = 2;
}

下一步就需要编译：

（1）当前目录直接编译：

protoc --cpp_out=. contact.proto

这段指令的含义如下：

protoc：表示 Protocol Buffers 的编译器程序（Protocol Compiler）。
--cpp_out=.：指定生成 C++ 语言的代码文件，并将生成的文件输出到当前目录（. 代表当前目录）。
contact.proto：需要被编译的 proto 文件，即你定义了消息结构的协议文件。

综合解释
这条命令的作用是：
使用 Protocol Buffers 的编译器 protoc，将 contact.proto 文件中定义的消息结构，自动生成对应的 C++ 源代码文件（通常为 contact.pb.h 和 contact.pb.cc），并把它们输出到当前目录下。

这样你就可以在 C++ 项目中直接包含和使用这些自动生成的代码了。

（2）指定目录编译

这种情况适用于当前没有处在contact.proto文件所在的目录时：

protoc -I contact_dir/ --cpp_out=contact_dir/ contact.proto

这段指令的含义如下：

protoc
Protocol Buffers 的编译器（protocol compiler）。
-I contact_dir/
指定包含 proto 文件的搜索目录（即 import 路径）。表示编译器在 contact_dir/ 目录下查找 proto 文件及其 import 的依赖。
--cpp_out=contact_dir/
指定输出目录为 contact_dir/，并生成 C++ 源代码（通常为 .pb.h 和 .pb.cc 文件）。
contact.proto
要编译的 proto 文件，定义了具体的数据结构。

综合解释：
这条命令会让 protoc 在 contact_dir/ 目录下查找 contact.proto，将其编译为 C++ 源代码，并把生成的 .pb.h 和 .pb.cc 文件输出到同样的 contact_dir/ 目录下。

这种写法常用于项目结构较复杂时，便于管理 proto 文件及生成的代码。

3、在业务中引入并使用生成的类

通过protoc编译proto文件之后，会生成下面两个文件：

// Generated by the protocol buffer compiler.  DO NOT EDIT!
// NO CHECKED-IN PROTOBUF GENCODE
// source: contact.proto
// Protobuf C++ Version: 6.31.0

#include "contact.pb.h"

#include <algorithm>
#include <type_traits>
#include "google/protobuf/io/coded_stream.h"
#include "google/protobuf/generated_message_tctable_impl.h"
#include "google/protobuf/extension_set.h"
#include "google/protobuf/generated_message_util.h"
#include "google/protobuf/wire_format_lite.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)

// Must be included last.
#include "google/protobuf/port_def.inc"
PROTOBUF_PRAGMA_INIT_SEG
namespace _pb = ::google::protobuf;
namespace _pbi = ::google::protobuf::internal;
namespace _fl = ::google::protobuf::internal::field_layout;
namespace contact {

inline constexpr Info::Impl_::Impl_(
    ::_pbi::ConstantInitialized) noexcept
      : _cached_size_{0},
        name_(
            &::google::protobuf::internal::fixed_address_empty_string,
            ::_pbi::ConstantInitialized()),
        age_{0} {}

template <typename>
PROTOBUF_CONSTEXPR Info::Info(::_pbi::ConstantInitialized)
#if defined(PROTOBUF_CUSTOM_VTABLE)
    : ::google::protobuf::Message(Info_class_data_.base()),
#else   // PROTOBUF_CUSTOM_VTABLE
    : ::google::protobuf::Message(),
#endif  // PROTOBUF_CUSTOM_VTABLE
      _impl_(::_pbi::ConstantInitialized()) {
}
struct InfoDefaultTypeInternal {
  PROTOBUF_CONSTEXPR InfoDefaultTypeInternal() : _instance(::_pbi::ConstantInitialized{}) {}
  ~InfoDefaultTypeInternal() {}
  union {
    Info _instance;
  };
};

PROTOBUF_ATTRIBUTE_NO_DESTROY PROTOBUF_CONSTINIT
    PROTOBUF_ATTRIBUTE_INIT_PRIORITY1 InfoDefaultTypeInternal _Info_default_instance_;
}  // namespace contact
static constexpr const ::_pb::EnumDescriptor *PROTOBUF_NONNULL *PROTOBUF_NULLABLE
    file_level_enum_descriptors_contact_2eproto = nullptr;
static constexpr const ::_pb::ServiceDescriptor *PROTOBUF_NONNULL *PROTOBUF_NULLABLE
    file_level_service_descriptors_contact_2eproto = nullptr;
const ::uint32_t
    TableStruct_contact_2eproto::offsets[] ABSL_ATTRIBUTE_SECTION_VARIABLE(
        protodesc_cold) = {
        0x081, // bitmap
        PROTOBUF_FIELD_OFFSET(::contact::Info, _impl_._has_bits_),
        5, // hasbit index offset
        PROTOBUF_FIELD_OFFSET(::contact::Info, _impl_.name_),
        PROTOBUF_FIELD_OFFSET(::contact::Info, _impl_.age_),
        0,
        1,
};

static const ::_pbi::MigrationSchema
    schemas[] ABSL_ATTRIBUTE_SECTION_VARIABLE(protodesc_cold) = {
        {0, sizeof(::contact::Info)},
};
static const ::_pb::Message* PROTOBUF_NONNULL const file_default_instances[] = {
    &::contact::_Info_default_instance_._instance,
};
const char descriptor_table_protodef_contact_2eproto[] ABSL_ATTRIBUTE_SECTION_VARIABLE(
    protodesc_cold) = {
    "\n\rcontact.proto\022\007contact\"!\n\004Info\022\014\n\004name"
    "\030\001 \001(\t\022\013\n\003age\030\002 \001(\005b\006proto3"
};
static ::absl::once_flag descriptor_table_contact_2eproto_once;
PROTOBUF_CONSTINIT const ::_pbi::DescriptorTable descriptor_table_contact_2eproto = {
    false,
    false,
    67,
    descriptor_table_protodef_contact_2eproto,
    "contact.proto",
    &descriptor_table_contact_2eproto_once,
    nullptr,
    0,
    1,
    schemas,
    file_default_instances,
    TableStruct_contact_2eproto::offsets,
    file_level_enum_descriptors_contact_2eproto,
    file_level_service_descriptors_contact_2eproto,
};
namespace contact {
// ===================================================================

class Info::_Internal {
 public:
  using HasBits =
      decltype(::std::declval<Info>()._impl_._has_bits_);
  static constexpr ::int32_t kHasBitsOffset =
      8 * PROTOBUF_FIELD_OFFSET(Info, _impl_._has_bits_);
};

Info::Info(::google::protobuf::Arena* PROTOBUF_NULLABLE arena)
#if defined(PROTOBUF_CUSTOM_VTABLE)
    : ::google::protobuf::Message(arena, Info_class_data_.base()) {
#else   // PROTOBUF_CUSTOM_VTABLE
    : ::google::protobuf::Message(arena) {
#endif  // PROTOBUF_CUSTOM_VTABLE
  SharedCtor(arena);
  // @@protoc_insertion_point(arena_constructor:contact.Info)
}
PROTOBUF_NDEBUG_INLINE Info::Impl_::Impl_(
    ::google::protobuf::internal::InternalVisibility visibility,
    ::google::protobuf::Arena* PROTOBUF_NULLABLE arena, const Impl_& from,
    const ::contact::Info& from_msg)
      : _has_bits_{from._has_bits_},
        _cached_size_{0},
        name_(arena, from.name_) {}

Info::Info(
    ::google::protobuf::Arena* PROTOBUF_NULLABLE arena,
    const Info& from)
#if defined(PROTOBUF_CUSTOM_VTABLE)
    : ::google::protobuf::Message(arena, Info_class_data_.base()) {
#else   // PROTOBUF_CUSTOM_VTABLE
    : ::google::protobuf::Message(arena) {
#endif  // PROTOBUF_CUSTOM_VTABLE
  Info* const _this = this;
  (void)_this;
  _internal_metadata_.MergeFrom<::google::protobuf::UnknownFieldSet>(
      from._internal_metadata_);
  new (&_impl_) Impl_(internal_visibility(), arena, from._impl_, from);
  _impl_.age_ = from._impl_.age_;

  // @@protoc_insertion_point(copy_constructor:contact.Info)
}
PROTOBUF_NDEBUG_INLINE Info::Impl_::Impl_(
    ::google::protobuf::internal::InternalVisibility visibility,
    ::google::protobuf::Arena* PROTOBUF_NULLABLE arena)
      : _cached_size_{0},
        name_(arena) {}

inline void Info::SharedCtor(::_pb::Arena* PROTOBUF_NULLABLE arena) {
  new (&_impl_) Impl_(internal_visibility(), arena);
  _impl_.age_ = {};
}
Info::~Info() {
  // @@protoc_insertion_point(destructor:contact.Info)
  SharedDtor(*this);
}
inline void Info::SharedDtor(MessageLite& self) {
  Info& this_ = static_cast<Info&>(self);
  this_._internal_metadata_.Delete<::google::protobuf::UnknownFieldSet>();
  ABSL_DCHECK(this_.GetArena() == nullptr);
  this_._impl_.name_.Destroy();
  this_._impl_.~Impl_();
}

inline void* PROTOBUF_NONNULL Info::PlacementNew_(
    const void* PROTOBUF_NONNULL, void* PROTOBUF_NONNULL mem,
    ::google::protobuf::Arena* PROTOBUF_NULLABLE arena) {
  return ::new (mem) Info(arena);
}
constexpr auto Info::InternalNewImpl_() {
  return ::google::protobuf::internal::MessageCreator::CopyInit(sizeof(Info),
                                            alignof(Info));
}
constexpr auto Info::InternalGenerateClassData_() {
  return ::google::protobuf::internal::ClassDataFull{
      ::google::protobuf::internal::ClassData{
          &_Info_default_instance_._instance,
          &_table_.header,
          nullptr,  // OnDemandRegisterArenaDtor
          nullptr,  // IsInitialized
          &Info::MergeImpl,
          ::google::protobuf::Message::GetNewImpl<Info>(),
#if defined(PROTOBUF_CUSTOM_VTABLE)
          &Info::SharedDtor,
          ::google::protobuf::Message::GetClearImpl<Info>(), &Info::ByteSizeLong,
              &Info::_InternalSerialize,
#endif  // PROTOBUF_CUSTOM_VTABLE
          PROTOBUF_FIELD_OFFSET(Info, _impl_._cached_size_),
          false,
      },
      &Info::kDescriptorMethods,
      &descriptor_table_contact_2eproto,
      nullptr,  // tracker
  };
}

PROTOBUF_CONSTINIT PROTOBUF_ATTRIBUTE_INIT_PRIORITY1 const
    ::google::protobuf::internal::ClassDataFull Info_class_data_ =
        Info::InternalGenerateClassData_();

PROTOBUF_ATTRIBUTE_WEAK const ::google::protobuf::internal::ClassData* PROTOBUF_NONNULL
Info::GetClassData() const {
  ::google::protobuf::internal::PrefetchToLocalCache(&Info_class_data_);
  ::google::protobuf::internal::PrefetchToLocalCache(Info_class_data_.tc_table);
  return Info_class_data_.base();
}
PROTOBUF_CONSTINIT PROTOBUF_ATTRIBUTE_INIT_PRIORITY1
const ::_pbi::TcParseTable<1, 2, 0, 25, 2>
Info::_table_ = {
  {
    PROTOBUF_FIELD_OFFSET(Info, _impl_._has_bits_),
    0, // no _extensions_
    2, 8,  // max_field_number, fast_idx_mask
    offsetof(decltype(_table_), field_lookup_table),
    4294967292,  // skipmap
    offsetof(decltype(_table_), field_entries),
    2,  // num_field_entries
    0,  // num_aux_entries
    offsetof(decltype(_table_), field_names),  // no aux_entries
    Info_class_data_.base(),
    nullptr,  // post_loop_handler
    ::_pbi::TcParser::GenericFallback,  // fallback
    #ifdef PROTOBUF_PREFETCH_PARSE_TABLE
    ::_pbi::TcParser::GetTable<::contact::Info>(),  // to_prefetch
    #endif  // PROTOBUF_PREFETCH_PARSE_TABLE
  }, {{
    // int32 age = 2;
    {::_pbi::TcParser::SingularVarintNoZag1<::uint32_t, offsetof(Info, _impl_.age_), 1>(),
     {16, 1, 0, PROTOBUF_FIELD_OFFSET(Info, _impl_.age_)}},
    // string name = 1;
    {::_pbi::TcParser::FastUS1,
     {10, 0, 0, PROTOBUF_FIELD_OFFSET(Info, _impl_.name_)}},
  }}, {{
    65535, 65535
  }}, {{
    // string name = 1;
    {PROTOBUF_FIELD_OFFSET(Info, _impl_.name_), _Internal::kHasBitsOffset + 0, 0,
    (0 | ::_fl::kFcOptional | ::_fl::kUtf8String | ::_fl::kRepAString)},
    // int32 age = 2;
    {PROTOBUF_FIELD_OFFSET(Info, _impl_.age_), _Internal::kHasBitsOffset + 1, 0,
    (0 | ::_fl::kFcOptional | ::_fl::kInt32)},
  }},
  // no aux_entries
  {{
    "\14\4\0\0\0\0\0\0"
    "contact.Info"
    "name"
  }},
};
PROTOBUF_NOINLINE void Info::Clear() {
// @@protoc_insertion_point(message_clear_start:contact.Info)
  ::google::protobuf::internal::TSanWrite(&_impl_);
  ::uint32_t cached_has_bits = 0;
  // Prevent compiler warnings about cached_has_bits being unused
  (void) cached_has_bits;

  cached_has_bits = _impl_._has_bits_[0];
  if ((cached_has_bits & 0x00000001u) != 0) {
    _impl_.name_.ClearNonDefaultToEmpty();
  }
  _impl_.age_ = 0;
  _impl_._has_bits_.Clear();
  _internal_metadata_.Clear<::google::protobuf::UnknownFieldSet>();
}

#if defined(PROTOBUF_CUSTOM_VTABLE)
::uint8_t* PROTOBUF_NONNULL Info::_InternalSerialize(
    const ::google::protobuf::MessageLite& base, ::uint8_t* PROTOBUF_NONNULL target,
    ::google::protobuf::io::EpsCopyOutputStream* PROTOBUF_NONNULL stream) {
  const Info& this_ = static_cast<const Info&>(base);
#else   // PROTOBUF_CUSTOM_VTABLE
::uint8_t* PROTOBUF_NONNULL Info::_InternalSerialize(
    ::uint8_t* PROTOBUF_NONNULL target,
    ::google::protobuf::io::EpsCopyOutputStream* PROTOBUF_NONNULL stream) const {
  const Info& this_ = *this;
#endif  // PROTOBUF_CUSTOM_VTABLE
  // @@protoc_insertion_point(serialize_to_array_start:contact.Info)
  ::uint32_t cached_has_bits = 0;
  (void)cached_has_bits;

  // string name = 1;
  if ((this_._impl_._has_bits_[0] & 0x00000001u) != 0) {
    if (!this_._internal_name().empty()) {
      const ::std::string& _s = this_._internal_name();
      ::google::protobuf::internal::WireFormatLite::VerifyUtf8String(
          _s.data(), static_cast<int>(_s.length()), ::google::protobuf::internal::WireFormatLite::SERIALIZE, "contact.Info.name");
      target = stream->WriteStringMaybeAliased(1, _s, target);
    }
  }

  // int32 age = 2;
  if ((this_._impl_._has_bits_[0] & 0x00000002u) != 0) {
    if (this_._internal_age() != 0) {
      target =
          ::google::protobuf::internal::WireFormatLite::WriteInt32ToArrayWithField<2>(
              stream, this_._internal_age(), target);
    }
  }

  if (ABSL_PREDICT_FALSE(this_._internal_metadata_.have_unknown_fields())) {
    target =
        ::_pbi::WireFormat::InternalSerializeUnknownFieldsToArray(
            this_._internal_metadata_.unknown_fields<::google::protobuf::UnknownFieldSet>(::google::protobuf::UnknownFieldSet::default_instance), target, stream);
  }
  // @@protoc_insertion_point(serialize_to_array_end:contact.Info)
  return target;
}

#if defined(PROTOBUF_CUSTOM_VTABLE)
::size_t Info::ByteSizeLong(const MessageLite& base) {
  const Info& this_ = static_cast<const Info&>(base);
#else   // PROTOBUF_CUSTOM_VTABLE
::size_t Info::ByteSizeLong() const {
  const Info& this_ = *this;
#endif  // PROTOBUF_CUSTOM_VTABLE
  // @@protoc_insertion_point(message_byte_size_start:contact.Info)
  ::size_t total_size = 0;

  ::uint32_t cached_has_bits = 0;
  // Prevent compiler warnings about cached_has_bits being unused
  (void)cached_has_bits;

  ::_pbi::Prefetch5LinesFrom7Lines(&this_);
  cached_has_bits = this_._impl_._has_bits_[0];
  if ((cached_has_bits & 0x00000003u) != 0) {
    // string name = 1;
    if ((cached_has_bits & 0x00000001u) != 0) {
      if (!this_._internal_name().empty()) {
        total_size += 1 + ::google::protobuf::internal::WireFormatLite::StringSize(
                                        this_._internal_name());
      }
    }
    // int32 age = 2;
    if ((cached_has_bits & 0x00000002u) != 0) {
      if (this_._internal_age() != 0) {
        total_size += ::_pbi::WireFormatLite::Int32SizePlusOne(
            this_._internal_age());
      }
    }
  }
  return this_.MaybeComputeUnknownFieldsSize(total_size,
                                             &this_._impl_._cached_size_);
}

void Info::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
  auto* const _this = static_cast<Info*>(&to_msg);
  auto& from = static_cast<const Info&>(from_msg);
  // @@protoc_insertion_point(class_specific_merge_from_start:contact.Info)
  ABSL_DCHECK_NE(&from, _this);
  ::uint32_t cached_has_bits = 0;
  (void) cached_has_bits;

  cached_has_bits = from._impl_._has_bits_[0];
  if ((cached_has_bits & 0x00000003u) != 0) {
    if ((cached_has_bits & 0x00000001u) != 0) {
      if (!from._internal_name().empty()) {
        _this->_internal_set_name(from._internal_name());
      } else {
        if (_this->_impl_.name_.IsDefault()) {
          _this->_internal_set_name("");
        }
      }
    }
    if ((cached_has_bits & 0x00000002u) != 0) {
      if (from._internal_age() != 0) {
        _this->_impl_.age_ = from._impl_.age_;
      }
    }
  }
  _this->_impl_._has_bits_[0] |= cached_has_bits;
  _this->_internal_metadata_.MergeFrom<::google::protobuf::UnknownFieldSet>(from._internal_metadata_);
}

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


void Info::InternalSwap(Info* PROTOBUF_RESTRICT PROTOBUF_NONNULL other) {
  using ::std::swap;
  auto* arena = GetArena();
  ABSL_DCHECK_EQ(arena, other->GetArena());
  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
  swap(_impl_._has_bits_[0], other->_impl_._has_bits_[0]);
  ::_pbi::ArenaStringPtr::InternalSwap(&_impl_.name_, &other->_impl_.name_, arena);
  swap(_impl_.age_, other->_impl_.age_);
}

::google::protobuf::Metadata Info::GetMetadata() const {
  return ::google::protobuf::Message::GetMetadataImpl(GetClassData()->full());
}
// @@protoc_insertion_point(namespace_scope)
}  // namespace contact
namespace google {
namespace protobuf {
}  // namespace protobuf
}  // namespace google
// @@protoc_insertion_point(global_scope)
PROTOBUF_ATTRIBUTE_INIT_PRIORITY2 static ::std::false_type
    _static_init2_ [[maybe_unused]] =
        (::_pbi::AddDescriptors(&descriptor_table_contact_2eproto),
         ::std::false_type{});
#include "google/protobuf/port_undef.inc"

// Generated by the protocol buffer compiler.  DO NOT EDIT!
// NO CHECKED-IN PROTOBUF GENCODE
// source: contact.proto
// Protobuf C++ Version: 6.31.0

#ifndef contact_2eproto_2epb_2eh
#define contact_2eproto_2epb_2eh

#include <limits>
#include <string>
#include <type_traits>
#include <utility>

#include "google/protobuf/runtime_version.h"
#if PROTOBUF_VERSION != 6031000
#error "Protobuf C++ gencode is built with an incompatible version of"
#error "Protobuf C++ headers/runtime. See"
#error "https://protobuf.dev/support/cross-version-runtime-guarantee/#cpp"
#endif
#include "google/protobuf/io/coded_stream.h"
#include "google/protobuf/arena.h"
#include "google/protobuf/arenastring.h"
#include "google/protobuf/generated_message_tctable_decl.h"
#include "google/protobuf/generated_message_util.h"
#include "google/protobuf/metadata_lite.h"
#include "google/protobuf/generated_message_reflection.h"
#include "google/protobuf/message.h"
#include "google/protobuf/message_lite.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)

// Must be included last.
#include "google/protobuf/port_def.inc"

#define PROTOBUF_INTERNAL_EXPORT_contact_2eproto

namespace google {
namespace protobuf {
namespace internal {
template <typename T>
::absl::string_view GetAnyMessageName();
}  // namespace internal
}  // namespace protobuf
}  // namespace google

// Internal implementation detail -- do not use these members.
struct TableStruct_contact_2eproto {
  static const ::uint32_t offsets[];
};
extern "C" {
extern const ::google::protobuf::internal::DescriptorTable descriptor_table_contact_2eproto;
}  // extern "C"
namespace contact {
class Info;
struct InfoDefaultTypeInternal;
extern InfoDefaultTypeInternal _Info_default_instance_;
extern const ::google::protobuf::internal::ClassDataFull Info_class_data_;
}  // namespace contact
namespace google {
namespace protobuf {
}  // namespace protobuf
}  // namespace google

namespace contact {

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


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

class Info final : public ::google::protobuf::Message
/* @@protoc_insertion_point(class_definition:contact.Info) */ {
 public:
  inline Info() : Info(nullptr) {}
  ~Info() PROTOBUF_FINAL;

#if defined(PROTOBUF_CUSTOM_VTABLE)
  void operator delete(Info* PROTOBUF_NONNULL msg, std::destroying_delete_t) {
    SharedDtor(*msg);
    ::google::protobuf::internal::SizedDelete(msg, sizeof(Info));
  }
#endif

  template <typename = void>
  explicit PROTOBUF_CONSTEXPR Info(::google::protobuf::internal::ConstantInitialized);

  inline Info(const Info& from) : Info(nullptr, from) {}
  inline Info(Info&& from) noexcept
      : Info(nullptr, ::std::move(from)) {}
  inline Info& operator=(const Info& from) {
    CopyFrom(from);
    return *this;
  }
  inline Info& operator=(Info&& from) noexcept {
    if (this == &from) return *this;
    if (::google::protobuf::internal::CanMoveWithInternalSwap(GetArena(), from.GetArena())) {
      InternalSwap(&from);
    } else {
      CopyFrom(from);
    }
    return *this;
  }

  inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const
      ABSL_ATTRIBUTE_LIFETIME_BOUND {
    return _internal_metadata_.unknown_fields<::google::protobuf::UnknownFieldSet>(::google::protobuf::UnknownFieldSet::default_instance);
  }
  inline ::google::protobuf::UnknownFieldSet* PROTOBUF_NONNULL mutable_unknown_fields()
      ABSL_ATTRIBUTE_LIFETIME_BOUND {
    return _internal_metadata_.mutable_unknown_fields<::google::protobuf::UnknownFieldSet>();
  }

  static const ::google::protobuf::Descriptor* PROTOBUF_NONNULL descriptor() {
    return GetDescriptor();
  }
  static const ::google::protobuf::Descriptor* PROTOBUF_NONNULL GetDescriptor() {
    return default_instance().GetMetadata().descriptor;
  }
  static const ::google::protobuf::Reflection* PROTOBUF_NONNULL GetReflection() {
    return default_instance().GetMetadata().reflection;
  }
  static const Info& default_instance() {
    return *reinterpret_cast<const Info*>(
        &_Info_default_instance_);
  }
  static constexpr int kIndexInFileMessages = 0;
  friend void swap(Info& a, Info& b) { a.Swap(&b); }
  inline void Swap(Info* PROTOBUF_NONNULL other) {
    if (other == this) return;
    if (::google::protobuf::internal::CanUseInternalSwap(GetArena(), other->GetArena())) {
      InternalSwap(other);
    } else {
      ::google::protobuf::internal::GenericSwap(this, other);
    }
  }
  void UnsafeArenaSwap(Info* PROTOBUF_NONNULL other) {
    if (other == this) return;
    ABSL_DCHECK(GetArena() == other->GetArena());
    InternalSwap(other);
  }

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

  Info* PROTOBUF_NONNULL New(::google::protobuf::Arena* PROTOBUF_NULLABLE arena = nullptr) const {
    return ::google::protobuf::Message::DefaultConstruct<Info>(arena);
  }
  using ::google::protobuf::Message::CopyFrom;
  void CopyFrom(const Info& from);
  using ::google::protobuf::Message::MergeFrom;
  void MergeFrom(const Info& from) { Info::MergeImpl(*this, from); }

  private:
  static void MergeImpl(::google::protobuf::MessageLite& to_msg,
                        const ::google::protobuf::MessageLite& from_msg);

  public:
  bool IsInitialized() const {
    return true;
  }
  ABSL_ATTRIBUTE_REINITIALIZES void Clear() PROTOBUF_FINAL;
  #if defined(PROTOBUF_CUSTOM_VTABLE)
  private:
  static ::size_t ByteSizeLong(const ::google::protobuf::MessageLite& msg);
  static ::uint8_t* PROTOBUF_NONNULL _InternalSerialize(
      const ::google::protobuf::MessageLite& msg, ::uint8_t* PROTOBUF_NONNULL target,
      ::google::protobuf::io::EpsCopyOutputStream* PROTOBUF_NONNULL stream);

  public:
  ::size_t ByteSizeLong() const { return ByteSizeLong(*this); }
  ::uint8_t* PROTOBUF_NONNULL _InternalSerialize(
      ::uint8_t* PROTOBUF_NONNULL target,
      ::google::protobuf::io::EpsCopyOutputStream* PROTOBUF_NONNULL stream) const {
    return _InternalSerialize(*this, target, stream);
  }
  #else   // PROTOBUF_CUSTOM_VTABLE
  ::size_t ByteSizeLong() const final;
  ::uint8_t* PROTOBUF_NONNULL _InternalSerialize(
      ::uint8_t* PROTOBUF_NONNULL target,
      ::google::protobuf::io::EpsCopyOutputStream* PROTOBUF_NONNULL stream) const final;
  #endif  // PROTOBUF_CUSTOM_VTABLE
  int GetCachedSize() const { return _impl_._cached_size_.Get(); }

  private:
  void SharedCtor(::google::protobuf::Arena* PROTOBUF_NULLABLE arena);
  static void SharedDtor(MessageLite& self);
  void InternalSwap(Info* PROTOBUF_NONNULL other);
 private:
  template <typename T>
  friend ::absl::string_view(::google::protobuf::internal::GetAnyMessageName)();
  static ::absl::string_view FullMessageName() { return "contact.Info"; }

 protected:
  explicit Info(::google::protobuf::Arena* PROTOBUF_NULLABLE arena);
  Info(::google::protobuf::Arena* PROTOBUF_NULLABLE arena, const Info& from);
  Info(
      ::google::protobuf::Arena* PROTOBUF_NULLABLE arena, Info&& from) noexcept
      : Info(arena) {
    *this = ::std::move(from);
  }
  const ::google::protobuf::internal::ClassData* PROTOBUF_NONNULL GetClassData() const PROTOBUF_FINAL;
  static void* PROTOBUF_NONNULL PlacementNew_(
      const void* PROTOBUF_NONNULL, void* PROTOBUF_NONNULL mem,
      ::google::protobuf::Arena* PROTOBUF_NULLABLE arena);
  static constexpr auto InternalNewImpl_();

 public:
  static constexpr auto InternalGenerateClassData_();

  ::google::protobuf::Metadata GetMetadata() const;
  // nested types ----------------------------------------------------

  // accessors -------------------------------------------------------
  enum : int {
    kNameFieldNumber = 1,
    kAgeFieldNumber = 2,
  };
  // string name = 1;
  void clear_name() ;
  const ::std::string& name() const;
  template <typename Arg_ = const ::std::string&, typename... Args_>
  void set_name(Arg_&& arg, Args_... args);
  ::std::string* PROTOBUF_NONNULL mutable_name();
  [[nodiscard]] ::std::string* PROTOBUF_NULLABLE release_name();
  void set_allocated_name(::std::string* PROTOBUF_NULLABLE value);

  private:
  const ::std::string& _internal_name() const;
  PROTOBUF_ALWAYS_INLINE void _internal_set_name(const ::std::string& value);
  ::std::string* PROTOBUF_NONNULL _internal_mutable_name();

  public:
  // int32 age = 2;
  void clear_age() ;
  ::int32_t age() const;
  void set_age(::int32_t value);

  private:
  ::int32_t _internal_age() const;
  void _internal_set_age(::int32_t value);

  public:
  // @@protoc_insertion_point(class_scope:contact.Info)
 private:
  class _Internal;
  friend class ::google::protobuf::internal::TcParser;
  static const ::google::protobuf::internal::TcParseTable<1, 2,
                                   0, 25,
                                   2>
      _table_;

  friend class ::google::protobuf::MessageLite;
  friend class ::google::protobuf::Arena;
  template <typename T>
  friend class ::google::protobuf::Arena::InternalHelper;
  using InternalArenaConstructable_ = void;
  using DestructorSkippable_ = void;
  struct Impl_ {
    inline explicit constexpr Impl_(::google::protobuf::internal::ConstantInitialized) noexcept;
    inline explicit Impl_(
        ::google::protobuf::internal::InternalVisibility visibility,
        ::google::protobuf::Arena* PROTOBUF_NULLABLE arena);
    inline explicit Impl_(
        ::google::protobuf::internal::InternalVisibility visibility,
        ::google::protobuf::Arena* PROTOBUF_NULLABLE arena, const Impl_& from,
        const Info& from_msg);
    ::google::protobuf::internal::HasBits<1> _has_bits_;
    ::google::protobuf::internal::CachedSize _cached_size_;
    ::google::protobuf::internal::ArenaStringPtr name_;
    ::int32_t age_;
    PROTOBUF_TSAN_DECLARE_MEMBER
  };
  union { Impl_ _impl_; };
  friend struct ::TableStruct_contact_2eproto;
};

extern const ::google::protobuf::internal::ClassDataFull Info_class_data_;

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




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


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

// Info

// string name = 1;
inline void Info::clear_name() {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  _impl_.name_.ClearToEmpty();
  _impl_._has_bits_[0] &= ~0x00000001u;
}
inline const ::std::string& Info::name() const
    ABSL_ATTRIBUTE_LIFETIME_BOUND {
  // @@protoc_insertion_point(field_get:contact.Info.name)
  return _internal_name();
}
template <typename Arg_, typename... Args_>
PROTOBUF_ALWAYS_INLINE void Info::set_name(Arg_&& arg, Args_... args) {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  _impl_._has_bits_[0] |= 0x00000001u;
  _impl_.name_.Set(static_cast<Arg_&&>(arg), args..., GetArena());
  // @@protoc_insertion_point(field_set:contact.Info.name)
}
inline ::std::string* PROTOBUF_NONNULL Info::mutable_name()
    ABSL_ATTRIBUTE_LIFETIME_BOUND {
  ::std::string* _s = _internal_mutable_name();
  // @@protoc_insertion_point(field_mutable:contact.Info.name)
  return _s;
}
inline const ::std::string& Info::_internal_name() const {
  ::google::protobuf::internal::TSanRead(&_impl_);
  return _impl_.name_.Get();
}
inline void Info::_internal_set_name(const ::std::string& value) {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  _impl_._has_bits_[0] |= 0x00000001u;
  _impl_.name_.Set(value, GetArena());
}
inline ::std::string* PROTOBUF_NONNULL Info::_internal_mutable_name() {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  _impl_._has_bits_[0] |= 0x00000001u;
  return _impl_.name_.Mutable( GetArena());
}
inline ::std::string* PROTOBUF_NULLABLE Info::release_name() {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  // @@protoc_insertion_point(field_release:contact.Info.name)
  if ((_impl_._has_bits_[0] & 0x00000001u) == 0) {
    return nullptr;
  }
  _impl_._has_bits_[0] &= ~0x00000001u;
  auto* released = _impl_.name_.Release();
  if (::google::protobuf::internal::DebugHardenForceCopyDefaultString()) {
    _impl_.name_.Set("", GetArena());
  }
  return released;
}
inline void Info::set_allocated_name(::std::string* PROTOBUF_NULLABLE value) {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  if (value != nullptr) {
    _impl_._has_bits_[0] |= 0x00000001u;
  } else {
    _impl_._has_bits_[0] &= ~0x00000001u;
  }
  _impl_.name_.SetAllocated(value, GetArena());
  if (::google::protobuf::internal::DebugHardenForceCopyDefaultString() && _impl_.name_.IsDefault()) {
    _impl_.name_.Set("", GetArena());
  }
  // @@protoc_insertion_point(field_set_allocated:contact.Info.name)
}

// int32 age = 2;
inline void Info::clear_age() {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  _impl_.age_ = 0;
  _impl_._has_bits_[0] &= ~0x00000002u;
}
inline ::int32_t Info::age() const {
  // @@protoc_insertion_point(field_get:contact.Info.age)
  return _internal_age();
}
inline void Info::set_age(::int32_t value) {
  _internal_set_age(value);
  _impl_._has_bits_[0] |= 0x00000002u;
  // @@protoc_insertion_point(field_set:contact.Info.age)
}
inline ::int32_t Info::_internal_age() const {
  ::google::protobuf::internal::TSanRead(&_impl_);
  return _impl_.age_;
}
inline void Info::_internal_set_age(::int32_t value) {
  ::google::protobuf::internal::TSanWrite(&_impl_);
  _impl_.age_ = value;
}

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

// @@protoc_insertion_point(namespace_scope)
}  // namespace contact


// @@protoc_insertion_point(global_scope)

#include "google/protobuf/port_undef.inc"

#endif  // contact_2eproto_2epb_2eh

假如在main函数中需要对PersonInfo类进行使用，需要包含生成的头文件，此外在编译的时候，还需要指定使用-std=c++11选项以及编译连接库 -lprotobuf。

示例：

#include<iostream>
#include"contact.pb.h"
#include<string>
using std::endl;
using std::cout;
using std::cerr;
int main()
{
    std::string people_str;
    {
        contact::PersonInfo info1;
        info1.set_age(21);
        info1.set_name("张三");
        if(!info1.SerializeToString(&people_str))
        {
            cerr<<"序列化失败"<<endl;
            exit(-1);
        }        
        cout<<"序列化成功"<<endl;
        cout<<"people_str:"<<people_str<<endl;
        cout<<"---------------------------------"<<endl;
    }
    {
        contact::PersonInfo info1;
        
        if(!info1.ParseFromString(people_str))
        {
            cerr<<"反序列化失败"<<endl;
            exit(-1);
        }        
        cout<<"反序列化成功"<<endl;
        cout<<"name:"<<info1.name()<<endl;
        cout<<"age:"<<info1.age()<<endl;
    }

    return 0;
}

运行结果：
在这里插入图片描述

4、在网络通信或存储中使用protobuf序列化数据

和本地是相同的，这里不再演示，在后面的讲解和实际项目中再详细展示。

四、快速上手写一个小需求来熟悉如何编写proto文件？

需求：我们正在开发一个简单的图书管理系统。需要在客户端和服务器之间传输图书信息。每本图书包含以下内容：

图书ID（整数）
书名（字符串）
作者（字符串）
出版年份（整数，可选）
是否借出（布尔值）
借阅人（字符串，可选，仅在借出时填写）

请根据这个需求，设计一个合适的proto文件。

比较完善的答案如下：

//声明语法版本
syntax = "proto3";

package books;

// 单本图书信息
message Book {
    int64 id = 1;                  // 图书ID
    string title = 2;              // 书名
    string author = 3;             // 作者
    int32 year = 4;                // 出版年份（可选，未知为0）
    bool is_borrowed = 5;          // 是否借出
    string borrower = 6;           // 借阅人（仅借出时填写，否则为空字符串）
}

完~
在这里插入图片描述