C++ protobuf示例

1、linux上安装protobuf3：

1）下载：

https://download.youkuaiyun.com/download/liuxiao723846/11584862

2）编译安装：

function check_install_status() {
    if [ $? -ne 0 ]; then
        echo "--!!ERROR"
        exit 1
    fi
}

#install protobuf3
if [ ! -d protobuf-3.6.0 ]; then
    tar -zxf protobuf-3.6.0.tar.gz
    cd protobuf-3.6.0
    ./autogen.sh
    ./autogen.sh && ./configure
        check_install_status
    make -j8
        check_install_status
    make install
        check_install_status
    cd python
    python setup.py install
        check_install_status
    ldconfig
    cd ../../
fi

2、简单示例：

1）person.proto:

package test;

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;
}

编译，生成C++代码：

$ protoc ./person.proto --cpp_out=./
$ ll
-rw-rw-r--. 1 roo roo  17237 Aug 20 21:19 person.pb.cc
-rw-rw-r--. 1 roo roo  12965 Aug 20 21:19 person.pb.h

2）编写C++业务代码：

#include <iostream>
#include <fstream>
#include "person.pb.h"
#include "google/protobuf/io/zero_copy_stream_impl.h"
#include "google/protobuf/text_format.h"


using namespace test;
int main(){
  Person p;
  p.set_name("test");
  p.set_id(1);
  p.set_email("a.iabc.com");

  //------------------将pb二进制信息保存到字符串
  std::string str;
  p.SerializeToString(&str);
  std::cout<<str<<std::endl;  
 
  //------------------将pb文本信息写入文件
  std::ofstream fw; 
  fw.open("./Person.txt", std::ios::out | std::ios::binary);
  google::protobuf::io::OstreamOutputStream *output = new google::protobuf::io::OstreamOutputStream(&fw);
  google::protobuf::TextFormat::Print(p, output);

  delete output;
  fw.close();

  //---------------------将pb文本信息保存到字符串
  std::string str1;
  google::protobuf::TextFormat::PrintToString(p, &str1);
  std::cout<<str1<<std::endl;

  //---------------------反序列化
  Person p1;
  p1.ParseFromString(str);
  std::cout<<"name:"<<p1.name()<<",email:"<<p1.email()<<std::endl;

  return 0;
}

3）编译、运行：

g++ -g -o run person_test.cpp ./person.pb.cc -I. -lprotobuf -pthread -std=c++11
或者
g++ -g -o run person_test.cpp ./person.pb.cc -I. -I/usr/local/protobuf/include -L/usr/local/protobuf/lib -lprotobuf -pthread -std=c++11

4）api说明：

• p.SerializeToString(&str)：将对象p序列化成二进制数据，保存到字符串中；
• 二进制虽然小，但是可读性差，所以通过google::protobuf::TextFormat::print()方法生成文本数据写入文件；为此需要引入google/protobuf/text_format.h(否则会报‘google::protobuf::TextFormat’ has not been declared错误)、zero_copy_stream_impl.h(否则会报OstreamOutputStream找不到)
• 除了将pb信息序列化成文本写入文件外，还可以调用google::protobuf::TextFormat::PrintToString(mrlist, &str1); 方法将pb文本信息保存到字符串中；（别忘了加text_format.h头文件）
• p1.ParseFromString(str);：将字符串中的二进制信息反序列成Person对象；
• C++版pb的api一般为：pb对象.set_消息属性(value)；设置属性值；pb对象.消息属性()；获取属性值；

3、复杂示例：

1）pb消息结构test.proto：

syntax = "proto2";
package video_stream;

message Item{
	optional string id = 1;
    optional float score = 2;
}
message ModelItems{
    optional string modelName = 1;
    repeated Item itemList = 2;
}
message ModelRecallInfoList{
    repeated ModelItems modelItemsList = 1;
}

message InnerUserPrefResponse {
	optional map<string, ModelItems> user_feed_map = 1;
}

编译：

$ protoc ./test.proto --cpp_out=./
$ ll
-rw-rw-r--. 1 roo roo  55676 Aug 20 23:28 test.pb.cc
-rw-rw-r--. 1 roo roo  32236 Aug 20 23:28 test.pb.h

2）c++业务代码：

#include <iostream>
#include <fstream>
#include "test.pb.h"
#include "google/protobuf/io/zero_copy_stream_impl.h"
#include "google/protobuf/text_format.h"

using namespace video_stream;

int main(){

  ModelRecallInfoList mrlist;
  ModelItems* items;
  Item* item;
  
  //model_item1
  items = mrlist.add_modelitemslist();
  items->set_modelname("model_items1");
  //item1
  item = items->add_itemlist(); 
  item->set_id("item1");
  item->set_score(0.9);
  //item2
  item = items->add_itemlist();
  item->set_id("item2");
  item->set_score(1.2);
  
  //model_items2
  items = mrlist.add_modelitemslist();
  items->set_modelname("model_items2");
  //item1
  item = items->add_itemlist();
  item->set_id("model_item2_item1");
  item->set_score(99.9);
  
  std::string str;
  mrlist.SerializeToString(&str);
  //std::cout<<str<<std::endl;

  std::string str1;
  google::protobuf::TextFormat::PrintToString(mrlist, &str1);
  std::cout<<str1<<std::endl;

  //---------------------------------------反序列化
  ModelRecallInfoList m;
  m.ParseFromString(str);
  int size = m.modelitemslist_size();
  for(int i=0;i<size;i++){
    ModelItems model_item  = m.modelitemslist(i);
    std::string model_name = model_item.modelname();
    int s1 = model_item.itemlist_size();
    std::string s;

    for(int j = 0;j<s1;j++){
      s+=model_item.itemlist(j).id()+",";
    }
    std::cout<<"modelName:"<<model_name<<",itemId:"<<s<<std::endl;
    
    //std::cout<<"modelName:"<<m.modelitemslist(i).modelname()<<std::endl;
  }
  
  //---------------------------------------放到map里
  InnerUserPrefResponse resp;
  auto* map = resp.mutable_user_feed_map(); 
  for (int i=0;i<size;i++){
    ModelItems model_item  = m.modelitemslist(i);
    std::string mn = model_item.modelname();
    (*map)[mn] = model_item; 
  }

  std::string str2;
  google::protobuf::TextFormat::PrintToString(resp, &str2);
  std::cout<<"=========================="<<std::endl;
  std::cout<<str2<<std::endl;
  return 0;
}

编译、运行：

g++ -g -o run test_main.cpp ./test.pb.cc -I. -lprotobuf -pthread -std=c++11

3）api说明：

pb对象中，子对象需要使用指针；

对于repeated类型：

pb对象.add_属性名() 添加一个子对象的指针；

pb对象.属性名_size()返回repeated大小；

pb对象.属性名(i)遍历其中一个子对象；

4、复杂消息示例2：

1）student.proto

package test;

message Address {
  optional string name = 1;
  optional string code = 2;
}
message Student {
  required string name = 1;
  required int32 id = 2;
  repeated string email = 3;
  optional Address ads = 4;
  map<string,string> other = 5;
}

编译

$ protoc ./student.proto --cpp_out=./
$ ll
-rw-rw-r--. 1 roo roo  55676 Aug 20 23:28 student.pb.cc
-rw-rw-r--. 1 roo roo  32236 Aug 20 23:28 student.pb.h

2）C++业务代码student_test.cpp：

#include <iostream>
#include "student.pb.h"
#include "google/protobuf/text_format.h"

using namespace test;

int main(){
  Student p;
  p.set_name("test");
  p.set_id(1);
  p.add_email("a.yxz.com");
  p.add_email("b.abc.com");
  std::string* e = p.add_email();
  *e = "c.iop.com";
  
  Address* ads = p.mutable_ads();
  ads->set_name("taiyuan");
  ads->set_code("0351");

  auto* map = p.mutable_other();  
  (*map)["biye"] = "nuc";
  (*map)["job"] = "abc";

  //============序列化成二进制
  std::string str;
  p.SerializeToString(&str);
  //std::cout<<str<<std::endl;  
 
  //============序列化成文本，打印
  std::string str1;
  google::protobuf::TextFormat::PrintToString(p, &str1);
  std::cout<<str1<<std::endl;
  
  //===========反序列化
  Student p1;
  p1.ParseFromString(str);
  int es = p1.email_size();
  std::string emails;
  for (int i=0;i<es;i++){
    emails += p1.email(i)+",";
  }

  Address adss= p1.ads();

  google::protobuf::Map<std::string,std::string> o = p1.other();
  google::protobuf::Map<std::string,std::string>::iterator ite;
  
  std::string others;
  for(ite=o.begin();ite!=o.end();ite++){
    others+=ite->first+":"+ite->second;
  }
  std::cout<<"name:"<<p1.name()<<";id:"<<p1.id()<<";emails:"<<emails<<";addreds:"<<adss.name()<<";other:"<<others<<std::endl;
  return 0;
}

3）说明：

• 可以看出来，对于子对象、map：设置值得时候一般需要用mutable_属性()；获取值一般用属性()
• 对于pb提供的api，可以在生成的.h文件中查看相应的方法；

补充：对于map的操作：

::google::protobuf::Map< ::std::string, ::std::string >* map = test.mutable_values();
cout << "size: " << f.values_size() << endl;   // size = 0
// add to map
(*map)["a"] = "a1";
(*map)["c"] = "a1";
(*map)["a"] = "a1";
cout << "size: " << f.values_size() << endl;   // size = 3

也可以使用下面：
auto& map = *test.mutable_values();
map["a"] = "a1";

参考：

https://developers.google.com/protocol-buffers/docs/reference/cpp-generated#map-fields

https://www.cnblogs.com/shine-lee/p/10701810.html

http://xcd.blog.techweb.com.cn/archives/173.html

https://www.cnblogs.com/tangxin-blog/p/8314563.html