1、在.proto檔案中定義訊息格式2、使用protobuf編譯器3、使用c++ api來讀寫訊息0、為何使用protobuf?1、原始記憶體資料結構，可以以二進位制方式sent/saved.這種方式需要相同的記憶體佈局和位元組序。2、以ad-hoc方式將資料項編碼成一個簡單字串----比如，將4個int型別編碼成"12:3:-23:67"。這種方式簡靈活。適用於簡單資料。3、將資料序列化為XML。這種方式很流行，因為xml可讀性好，編碼解碼方便，效能也好。僅僅XML dom樹比較複雜。protobuf可以很好的解決上述問題。你編寫一個.proto檔案來描述資料結構。protobuf編譯器使用它建立一個類，使用二進位制方式自動編碼/解碼該資料結構。生成的類提供getter/setter方法。最重要的是，protobuf支援在此基礎上進行格式擴充套件。示例1
 
、定義協議格式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; }該結構與c++或java很像..proto檔案以包宣告開始，防止名字衝突。簡單型別：bool, int32, float, double, string.其它型別：如上述的Person, PhoneNumber型別可以巢狀。“=1”， “=2”標識唯一“tag”.tag數1-15需要至少一個位元組。required: 必須設定它的值optional: 可以設定，也可以不設定它的值repeated: 可以認為是動態分配的陣列google工程師認為使用required威害更大， 他們更喜歡使用optional, repeated.2
 
、編譯你的協議執行protoc 來生成c++檔案：protoc -I=$SRC_DIR --cpp_out=$DST_DIR $SRC_DIR/addressbook.protoprotoc -I=./ --cpp_out=./ ./addressbook.proto生成的檔案為：addressbook.pb.h, addressbook.pb.cc3、protobuf API生成的檔案中有如下方法：// 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、列舉與巢狀類生成的程式碼包含一個PhoneType列舉。Person::PhoneType, Person:MOBILE, Person::HOME, Person:WORK.編譯器生成的巢狀類稱為Person::PhoneNumber. 實際生成類為Person_PhoneNumber.5、標準方法bool IsInitialized() const:                確認required欄位是否被設定string DebugString() const:                返回訊息的可讀表示，用於除錯void CopyFrom(const Person& from):         使用給定訊息值copyvoid Clear():                              清除所有元素為空狀態6、解析與序列化bool SerializeToString(string* output) const:        序列化訊息，將儲存位元組的以string方式輸出。注意位元組是二進位制，而非文字；bool ParseFromString(const string& data):            解析給定的string     bool SerializeToOstream(ostream* output) const:      寫訊息給定的c++  ostream中bool ParseFromIstream(istream* input):               從給定的c++ istream中解析出訊息7、protobuf和 oo設計不要繼承生成類並在此基礎上新增相應的行為8、寫訊息示例：它從一個檔案中讀取AddressBook，基於io新增一個新的Person，並將新的AddressBook寫回檔案。#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巨集。每一個.pb.cc檔案在啟動時都將自動呼叫該巨集。注意在程式結尾處呼叫ShutdownProtobufLibrary()。9、讀訊息 #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、擴充套件protobuf如果希望向後相容，必須遵循：a、不必更改tag數b、不必新增或刪除任何required欄位c、可以刪除optional或repeated欄位d、可以新增新的optional或repeated欄位，但你必須使用新的tag數。11、優化c++的protobuf庫，已經極大地優化了。合理使用可以改善效能。a、如果可能，複用message物件。b、關於多執行緒的記憶體分配器12、高階用法protobuf的訊息類的一個關鍵特性是，反射(reflection)。可以使用xml或json來實現。參考。================================================================常見問題：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