c++使用protobuf

转：https://www.cnblogs.com/zhouyang209117/p/7218719.html

使用场景

假定现在要实现一个保存和显示用户通讯录的功能.如里不用protocbuf,思路大概是这样的:提示用户输入姓名,电话号码之类,然后保存到文件,文件可以是xml,csv之类.读取的时候要解析xml或者csv,然后再把文件中的数据装入内存.这个思路完全能实现功能,问题是读写的时候都要涉及文件操作.protocbuf可以简化这个操作,存的时候直接按对象存,取的时候按对象取,效率极高.

环境

• ubuntu 16.04.2
• protocbuf 2.6.1
• g++ 5.4.0

使用

1. 定义proto文件addressbook.proto,addressbook.proto中定义了通讯录的一些信息.

syntax = "proto2";
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 phones = 4;
}
message AddressBook {
    repeated Person people = 1;
}

1. 把proto文件转化成c++代码.执行下面命令.

protoc --cpp_out=. addressbook.proto

     2.完成读写数据的代码.

写数据write_data.cpp

#include 
#include 
#include 
#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');//忽略最后的回车

    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_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;
        }
    }
}
// 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_people());
    {
        // 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;
}

读数据read_data.cpp

#include 
#include 
#include 
#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.people_size(); i++) {
        const tutorial::Person &person = address_book.people(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.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;
            }
            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;
}

编译成可执行文件