Caffe代码导读(1):Protobuf例子-阿里云开发者社区

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Caffe代码导读(1):Protobuf例子

简介:

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): zhaoyongke@yeah.net
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: zhaoyongke@yeah.net
  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。

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