Google 的Protobuf 技术详解

1、例子

官方例子，建立一个 test.proto 内容如下：

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;
}

2、注意

1、首先 .proto 文件 要有一个 package declaration；

2、 message可以理解为一个类，变量可以使用如下声明【bool, int32, float, double, string】, 同时message可以嵌套定义。

3、message内可以定义enum。

4、message中的数字 =1，或=2 是为了二进制独立编码。1-15 占空间少，可提升效率。16以后占空间大，效率低。因此将常用的那些变量定义为1-15，提高效率。

5、message中的每个filed必须有prefix-修饰词，这些限定词可以是【required，optional，repeated】。

3、结果

protoc –cpp_out=$DST_DIR your/*.proto

可以生成***.pb.h 和***.pb.cc

编译后会生成api。

getters have exactly the name as the field in lowercase, and the setter methods begin with set_

There are also has_ methods for each singular (required or optional) field which return true if that field has been set. Finally, each field has a clear_ method that un-sets the field back to its empty state.

string 还有 mutable_ 方法返回指针。

4、调用方法

#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_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;
}

Ref: https://developers.google.com/protocol-buffers/docs/cpptutorial