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Catalogue
  1. 1. 1. Protobuf
  2. 2. 2. Protobuf-Tutorials 应用举例
    1. 2.1. 2.1. 定义格式
    2. 2.2. 2.2. addressBook.proto
    3. 2.3. 2.3. 编译protobuf，生成消息类
      1. 2.3.1. 2.3.1. addressbook.pb.h
    4. 2.4. 2.4. 解析和序列化
    5. 2.5. 2.5. C++调用
      1. 2.5.1. 2.5.1. 示例：将个人详细信息写入地址簿文件
        1. 2.5.1.1. 2.5.1.1. 运行效果
      2. 2.5.2. 2.5.2. 示例：从地址簿文件读取信息
        1. 2.5.2.1. 2.5.2.1. 运行效果

1. Protobuf

Protobuf是一种平台无关、语言无关、可扩展且轻便高效的序列化数据结构的协议，可以用于网络通信和数据存储

2. Protobuf-Tutorials 应用举例

Tutorials示例：一个非常简单的“地址簿”应用程序，它可以在文件中读取和写入人们的联系方式。通讯录中的每个人都有一个姓名，一个ID，一个电子邮件地址和一个联系电话

  • 在.proto 文件中定义消息格式
  • 使用protocol buffer编译器
  • 使用C++ protocol buffer API读写消息

使用protobuf，可以编写.proto文件来描述要储存的数据结构，protobuf编译器会创建一个类，该类以有效的二进制格式实现协议缓冲区数据的自动编码和解析。生成的类为构成协议缓冲区的字段提供获取器和设置器，并以协议为单位来详细阅读和写入协议缓冲区。重要的是，协议缓冲区格式支持随时间扩展格式的想法，以使代码仍可以读取以旧格式编码的数据。

2.1. 定义格式

为了创建“地址簿”应用程序，需要从.proto 文件开始。.proto 中的定义很简单：把要序列化的每个数据结构添加一条nessage，然后为消息中的每个字段指定名称和类型。

2.2. addressBook.proto

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syntax = "proto3";
package tutorial;

import "google/protobuf/timestamp.proto";
// [END declaration]

// [START java_declaration]
option java_package = "com.example.tutorial";
option java_outer_classname = "AddressBookProtos";
// [END java_declaration]

// [START csharp_declaration]
option csharp_namespace = "Google.Protobuf.Examples.AddressBook";
// [END csharp_declaration]

// [START messages]
message Person {
  string name = 1;
  int32 id = 2;  // Unique ID number for this person.
  string email = 3;

  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }

  message PhoneNumber {
    string number = 1;
    PhoneType type = 2;
  }

  repeated PhoneNumber phones = 4;

  google.protobuf.Timestamp last_updated = 5;
}

// Our address book file is just one of these.
message AddressBook {
  repeated Person people = 1;
}
// [END messages]
}

该.proto文件以程序包声明开头，这有助于防止不同项目之间的命名冲突。在C ++中，您生成的类将放置在与程序包名称匹配的名称空间中。

在上述示例中:

  • Person消息包含PhoneNumber消息，
  • 而AddressBook消息包含Person消息
  • 甚至可以定义嵌套在其他消息中的消息类型
  • 每个元素上的“ = 1”，“ = 2”标记标识该字段在二进制编码中使用的唯一“标记”

2.3. 编译protobuf，生成消息类

既然有了.proto，接下来需要做的是生成读取和写入AddressBook（Person和PhoneNumber）消息所需的类。

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protoc -I=$SRC_DIR --cpp_out=$DST_DIR $SRC_DIR/addressbook.proto

执行上述编译指令之后，将会在目的目录得到消息类文件：

  • addressbook.pb.h
  • addressbook.pb.cc

2.3.1. addressbook.pb.h

对于上述定义的字段，可以看到生成了这些类：

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namespace tutorial {
class AddressBook;
class AddressBookDefaultTypeInternal;
extern AddressBookDefaultTypeInternal _AddressBook_default_instance_;
class Person;
class PersonDefaultTypeInternal;
extern PersonDefaultTypeInternal _Person_default_instance_;
class Person_PhoneNumber;
class Person_PhoneNumberDefaultTypeInternal;
extern Person_PhoneNumberDefaultTypeInternal _Person_PhoneNumber_default_instance_;
}  // namespace tutorial

对应的UML类图

2.4. 解析和序列化

  • bool SerializeToString(string* output) const;：序列化消息并将字节存储在给定的字符串中。请注意，字节是二进制的，而不是文本；我们仅将string类用作方便的容器。
  • bool ParseFromString(const string& data);:解析来自给定字符串的消息
  • bool SerializeToOstream(ostream* output) const;: 将消息写入给定的C ++ ostream
  • bool ParseFromIstream(istream* input);: 解析来自给定C ++的消息istream

2.5. C++调用

2.5.1. 示例：将个人详细信息写入地址簿文件

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#include <ctime>
#include <fstream>
#include <google/protobuf/util/time_util.h>
#include <iostream>
#include <string>

#include "addressbook.pb.h"

using namespace std;

using google::protobuf::util::TimeUtil;

void PromptForAddress(tutorial::Person* person) {
    //设置ID
    cout << "Enter person ID number: ";
    int id;
    cin >> id;
    person->set_id(id);
    cin.ignore(256, '\n');

    //设置name
    cout << "Enter name: ";
    getline(cin, *person->mutable_name());

    //设置email
    cout << "Enter email address (blank for none): ";
    string email;
    getline(cin, email);
    if (!email.empty()) {
        person->set_email(email);
    }

    //设置phone
    while (true) {
        cout << "Enter a phone number (or leave blank to finish): ";
        string number;
        getline(cin, number);
        if (number.empty()) {
            break;
        }

        tutorial::Person::PhoneNumber* phone_number = person->add_phones();
        phone_number->set_number(number);

        cout << "Is this a mobile, home, or work phone? ";
        string type;
        getline(cin, type);
        if (type == "mobile") {
            phone_number->set_type(tutorial::Person::MOBILE);
        } else if (type == "home") {
            phone_number->set_type(tutorial::Person::HOME);
        } else if (type == "work") {
            phone_number->set_type(tutorial::Person::WORK);
        } else {
            cout << "Unknown phone type.  Using default." << endl;
        }
    }
    //时间戳
    *person->mutable_last_updated() = TimeUtil::SecondsToTimestamp(time(NULL));
}

int main(int argc, char* argv[]) {
    // 宏定义用于确定protobuf版本,版本不一致则抛出异常
    GOOGLE_PROTOBUF_VERIFY_VERSION;

    //输入一个文件，如果没有，则会新建一个
    if (argc != 2) {
        cerr << "Usage:  " << argv[0] << " ADDRESS_BOOK_FILE" << endl;
        return -1;
    }
    //这是由.proto编译生成的类
    tutorial::AddressBook address_book;

    //尝试从已有数据文件读取,没有则创建
    {
        // Read the existing address book.
        fstream input(argv[1], ios::in | ios::binary);
        if (!input) {
            cout << argv[1] << ": File not found.  Creating a new file." << endl;
        } else if (!address_book.ParseFromIstream(&input)) {
            cerr << "Failed to parse address book." << endl;
            return -1;
        }
    }

    //地址簿新增一个人的信息
    PromptForAddress(address_book.add_people());
    //保存到文件
    {
        //准备输出
        fstream output(argv[1], ios::out | ios::trunc | ios::binary);
        // 序列化输出
        if (!address_book.SerializeToOstream(&output)) {
            cerr << "Failed to write address book." << endl;
            return -1;
        }
    }

    // Optional:  Delete all global objects allocated by libprotobuf.
    google::protobuf::ShutdownProtobufLibrary();

    return 0;
}

CMakeList.txt

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cmake_minimum_required(VERSION 2.8)

project(protobuf3_learn)
set(CMAKE_INCLUDE_CURRENT_DIR TRUE)

# Find required protobuf package
find_package(protobuf CONFIG REQUIRED)

if(protobuf_VERBOSE)
  message(STATUS "Using Protocol Buffers ${Protobuf_VERSION}")
endif()

add_executable(addFile addressbook.pb.cc add_person.cc )
target_link_libraries(addFile  protobuf::libprotobuf)

2.5.1.1. 运行效果

2.5.2. 示例：从地址簿文件读取信息

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// See README.txt for information and build instructions.

#include <fstream>
#include <google/protobuf/util/time_util.h>
#include <iostream>
#include <string>

#include "addressbook.pb.h"

using namespace std;

using google::protobuf::util::TimeUtil;

//读取信息
void ListPeople(const tutorial::AddressBook& address_book) {
  for (int i = 0; i < address_book.people_size(); i++) {
    const tutorial::Person& person = address_book.people(i);

    cout << "Person ID: " << person.id() << endl;
    cout << "  Name: " << person.name() << endl;
    if (person.email() != "") {
      cout << "  E-mail address: " << person.email() << endl;
    }

    for (int j = 0; j < person.phones_size(); j++) {
      const tutorial::Person::PhoneNumber& phone_number = person.phones(j);

      switch (phone_number.type()) {
        case tutorial::Person::MOBILE:
          cout << "  Mobile phone #: ";
          break;
        case tutorial::Person::HOME:
          cout << "  Home phone #: ";
          break;
        case tutorial::Person::WORK:
          cout << "  Work phone #: ";
          break;
        default:
          cout << "  Unknown phone #: ";
          break;
      }
      cout << phone_number.number() << endl;
    }
    if (person.has_last_updated()) {
      cout << "  Updated: " << TimeUtil::ToString(person.last_updated()) << endl;
    }
  }
}

// Main function:  Reads the entire address book from a file and prints all
//   the information inside.
int main(int argc, char* argv[]) {
  // Verify that the version of the library that we linked against is
  // compatible with the version of the headers we compiled against.
  GOOGLE_PROTOBUF_VERIFY_VERSION;

  if (argc != 2) {
    cerr << "Usage:  " << argv[0] << " ADDRESS_BOOK_FILE" << endl;
    return -1;
  }

  tutorial::AddressBook address_book;

  {
    // Read the existing address book.
    fstream input(argv[1], ios::in | ios::binary);
    if (!address_book.ParseFromIstream(&input)) {
      cerr << "Failed to parse address book." << endl;
      return -1;
    }
  }

  ListPeople(address_book);

  // Optional:  Delete all global objects allocated by libprotobuf.
  google::protobuf::ShutdownProtobufLibrary();

  return 0;
}
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cmake_minimum_required(VERSION 2.8)

project(protobuf3_learn)
set(CMAKE_INCLUDE_CURRENT_DIR TRUE)

# Find required protobuf package
find_package(protobuf CONFIG REQUIRED)

if(protobuf_VERBOSE)
  message(STATUS "Using Protocol Buffers ${Protobuf_VERSION}")
endif()


add_executable(addFile addressbook.pb.cc add_person.cc )
add_executable(readFile addressbook.pb.cc list_people.cc)
target_link_libraries(addFile  protobuf::libprotobuf)
target_link_libraries(readFile  protobuf::libprotobuf)

2.5.2.1. 运行效果