Caffe代码解读：Protobuf

转载：http://blog.csdn.net/kkk584520/article/details/41046827

protobuf下载地址：http://pan.baidu.com/s/1pJlZubT

Protobuf是一种可以实现内存与外存交换的协议接口。这是由谷歌开发的开源工具，目前研究Caffe源码时用到。

一个软件项目 = 数据结构 + 算法 + 参数，对于数据结构和算法我们都已经有较多研究，但不同开发者对参数管理却各有千秋。有人喜欢TXT格式化的参数文件，有人喜欢BIN简单高效，也有人喜欢图形化界面的直观。不一致的参数管理带来很多问题，例如一个项目组内不同成员必须约定一套统一的参数方案，或者称为通信协议，这样便于模块集成。而Protobuf工具就完美解决了这个问题，关键部分代码自动生成，节省了大量的开发、调试时间。

首先下载protobuf，地址（打不开？……不解释）

这里用Linux版本2.5.0

解压：

tar zxvf protobuf-2.5.0.tar.gz

切到主目录：

cd protobuf-2.5.0

编译：

./configure

make

sudo make install

添加环境变量：

export PKG_CONFIG_PATH=$(pwd)

编译examples:

cd examples/

make cpp

这里我们只编译C++代码。

编译完成，生成了以下可执行文件：

add_person_cpp

list_people_cpp

这是个通讯录的例子。我们首先运行add_person_cpp：

 ./add_person_cpp zyk
 zyk: File not found.  Creating a new file.
 Enter person ID number: 123
 Enter name: zhaoyongke
 Enter email address (blank for none): [email protected]
 Enter a phone number (or leave blank to finish): 188188188
 Is this a mobile, home, or work phone?（回车）
 Unknown phone type.  Using default.
 Enter a phone number (or leave blank to finish):（回车）

然后运行list_people_cpp：

 ./list_people_cpp zyk
 Person ID: 123
   Name: zhaoyongke
   E-mail address: [email protected]
   Home phone #: 188188188

可见我们生成了新的通讯录zyk，里面保存了相应的信息。

例子运行结束了，我们看下代码是如何生成的。

protobuf使用前，先编写proto文件，这是描述我们需要配置参数的数据结构。这个例子里面的proto如下：

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

 package tutorial;

 option java_package = "com.example.tutorial";
 option java_outer_classname = "AddressBookProtos";

 message Person {
   required string name = 1;
   required int32 id = 2;        // Unique ID number for this person.
   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;
 }

 // Our address book file is just one of these.
 message AddressBook {
   repeated Person person = 1;
 }

前几行是定义包的，可以忽略。

message Person{...}定义了一个需要传输的参数结构体，可见包括这么几个单元：name（string类型）、id（int32类型）、email（string类型）、phone（PhoneNumber类型，嵌套在Person内的类）。前面标记为“required”是必须有值的，而“optional“则为可选项，”repeated“表示后面单元为相同类型的一组向量。

有了如上定义，我们可以用protobuf工具生成接口代码，命令如下：

 protoc --cpp_out=.  addressbook.proto

运行后生成了两个文件：addressbook.pb.cc 和addressbook.pb.h，代码比较长就不贴了。我们的应用程序可以通过自动生成的接口实现参数的序列化/反序列化，代码如下：

 //add_person.c
 #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;
 }

可见只需要调用addressbook.pb.h中声明的tutorial::AddressBook类、Person类中的接口（add_person(), add_phone(), set_number(), set_email()等）就能操作相应的参数，最后将内存中的参数序列化为文件只需要执行SerializeToOstream()。相应的读取参数文件的操作为ParseFromIstream()。这里贴出例子中的第二个程序如下：

 // list_people.c

 #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;
 }

相信做完这个实验，你将不再对Caffe代码中的参数初始化、参数保存操作感到陌生，一切都很自然。

 除了上述简单功能，Protobuf还可以用来传递不同语言(C/C++与Java、Python)之间的参数，省去了自己手动维护数据结构的繁琐工作。也可以支持客户端/服务器模式，在主机/从机之间传递参数。