1、在.proto文件中定义消息格式2、使用protobuf编译器3、使用c++ api来读写消息0、为何使用protobuf?1、原始内存数据结构，可以以二进制方式sent/saved.这种方式需要相同的内存布局和字节序。2、以ad-hoc方式将数据项编码成一个简单字符串----比如，将4个int类型编码成"12:3:-23:67"。这种方式简灵活。适用于简单数据。3、将数据序列化为XML。这种方式很流行，因为xml可读性好，编码解码方便，性能也好。仅仅XML dom树比较复杂。protobuf可以很好的解决上述问题。你编写一个.proto文件来描述数据结构。protobuf编译器使用它创建一个类，使用二进制方式自动编码/解码该数据结构。生成的类提供getter/setter方法。最重要的是，protobuf支持在此基础上进行格式扩展。示例1、定义协议格式package tutorial;  message Person {   required string name = 1;   required int32 id = 2;   optional string email = 3;       enum PhoneType {        MOBILE = 0;        HOME = 1;        WORK = 2;   }   message PhoneNumber {        required string number = 1;        optional PhoneType type = 2 [default = HOME];      }   repeated PhoneNumber phone = 4; }  message AddressBook {   repeated Person person = 1; }该结构与c++或java很像..proto文件以包声明开始，防止名字冲突。简单类型：bool, int32, float, double, string.其它类型：如上述的Person, PhoneNumber类型可以嵌套。“=1”， “=2”标识唯一“tag”.tag数1-15需要至少一个字节。required: 必须设置它的值optional: 可以设置，也可以不设置它的值repeated: 可以认为是动态分配的数组google工程师认为使用required威害更大， 他们更喜欢使用optional, repeated.2、编译你的协议运行protoc 来生成c++文件：protoc -I=$SRC_DIR --cpp_out=$DST_DIR $SRC_DIR/addressbook.protoprotoc -I=./ --cpp_out=./ ./addressbook.proto生成的文件为：addressbook.pb.h, addressbook.pb.cc3、protobuf API生成的文件中有如下方法：// name  inline bool has_name() const;  inline void clear_name();  inline const ::std::string& name() const;  inline void set_name(const ::std::string& value);  inline void set_name(const char* value);  inline ::std::string* mutable_name();  // id  inline bool has_id() const;  inline void clear_id();  inline int32_t id() const;  inline void set_id(int32_t value);  // email  inline bool has_email() const;  inline void clear_email();  inline const ::std::string& email() const;  inline void set_email(const ::std::string& value);  inline void set_email(const char* value);  inline ::std::string* mutable_email();  // phone  inline int phone_size() const;  inline void clear_phone();  inline const ::google::protobuf::RepeatedPtrField< ::tutorial::Person_PhoneNumber >& phone() const;  inline ::google::protobuf::RepeatedPtrField< ::tutorial::Person_PhoneNumber >* mutable_phone();  inline const ::tutorial::Person_PhoneNumber& phone(int index) const;  inline ::tutorial::Person_PhoneNumber* mutable_phone(int index);  inline ::tutorial::Person_PhoneNumber* add_phone();4、枚举与嵌套类生成的代码包含一个PhoneType枚举。Person::PhoneType, Person:MOBILE, Person::HOME, Person:WORK.编译器生成的嵌套类称为Person::PhoneNumber. 实际生成类为Person_PhoneNumber.5、标准方法bool IsInitialized() const:                确认required字段是否被设置string DebugString() const:                返回消息的可读表示，用于调试void CopyFrom(const Person& from):         使用给定消息值copyvoid Clear():                              清除所有元素为空状态6、解析与序列化bool SerializeToString(string* output) const:        序列化消息，将存储字节的以string方式输出。注意字节是二进制，而非文本；bool ParseFromString(const string& data):            解析给定的string     bool SerializeToOstream(ostream* output) const:      写消息给定的c++  ostream中bool ParseFromIstream(istream* input):               从给定的c++ istream中解析出消息7、protobuf和 oo设计不要继承生成类并在此基础上添加相应的行为8、写消息示例：它从一个文件中读取AddressBook，基于io添加一个新的Person，并将新的AddressBook写回文件。#include <iostream>#include <fstream>#include <string>#include "addressbook.pb.h"using namespace std;// This function fills in a Person message based on user input.void PromptForAddress(tutorial::Person* person) {  cout << "Enter person ID number: ";  int id;  cin >> id;  person->set_id(id);  cin.ignore(256, '\n');  cout << "Enter name: ";  getline(cin, *person->mutable_name());  cout << "Enter email address (blank for none): ";  string email;  getline(cin, email);  if (!email.empty()) {    person->set_email(email);  }  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_phone();    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;    }  }}// Main function:  Reads the entire address book from a file,//   adds one person based on user input, then writes it back out to the same//   file.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 (!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;    }  }  // Add an address.  PromptForAddress(address_book.add_person());  {    // Write the new address book back to disk.    fstream output(argv[1], ios::out | ios::trunc | ios::binary);    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;}注意使用GOOGLE_PROTOBUF_VERIFY_VERSION宏。每一个.pb.cc文件在启动时都将自动调用该宏。注意在程序结尾处调用ShutdownProtobufLibrary()。9、读消息 #include <iostream>#include <fstream>#include <string>#include "addressbook.pb.h"using namespace std;// Iterates though all people in the AddressBook and prints info about them.void ListPeople(const tutorial::AddressBook& address_book) {  for (int i = 0; i < address_book.person_size(); i++) {    const tutorial::Person& person = address_book.person(i);    cout << "Person ID: " << person.id() << endl;    cout << "  Name: " << person.name() << endl;    if (person.has_email()) {      cout << "  E-mail address: " << person.email() << endl;    }    for (int j = 0; j < person.phone_size(); j++) {      const tutorial::Person::PhoneNumber& phone_number = person.phone(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;      }      cout << phone_number.number() << 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;}10、扩展protobuf如果希望向后兼容，必须遵循：a、不必更改tag数b、不必添加或删除任何required字段c、可以删除optional或repeated字段d、可以添加新的optional或repeated字段，但你必须使用新的tag数。11、优化c++的protobuf库，已经极大地优化了。合理使用可以改善性能。a、如果可能，复用message对象。b、关于多线程的内存分配器12、高级用法protobuf的消息类的一个关键特性是，反射(reflection)。可以使用xml或json来实现。参考。================================================================常见问题：1、undefined reference to `pthread_once' 使用-lpthread:2、error while loading shared libraries: libprotobuf.so.7: cannot open shared object file: No such file or directory使用-Wl,-Bstatic -lprotobuf -Wl,-Bdynamic -lpthread