Protobuf compound data types, speaking, reading and writing

背景

protobuf 在生成的 C++ 代码中为 .proto 文件中的每个 message 生成了对应的 C++ 类,并提供了数据成员的读写方法.

message 类型读写

①．message 示例

message Point
{
    
   double lng = 1;
   double lat = 2;
}
message DemoMsg
{
    
   int32 id = 1;
   Point pos = 2;
}

②．成员赋值

通过 mutable_xxx The method returns a pointer to member assignment：

 protoTest::DemoMsg msg; 
 msg.set_id(100);
 
 msg.mutable_pos()->set_lng(112.56);
 msg.mutable_pos()->set_lat(56.78);
 cout << msg.DebugString() << endl;

通过 copyFrom Method uses struct assignment：

protoTest::DemoMsg msg; 
msg.set_id(100);

protoTest::Point m_p;
m_p.set_lng(112.56);
m_p.set_lat(56.78);

msg.mutable_pos()->CopyFrom(m_p);
cout << msg.DebugString() << endl;

通过 set_allocated_xxx Member functions pass in pointers for assignment：

protoTest::DemoMsg msg; 
msg.set_id(100);

protoTest::Point * m_p = new  protoTest::Point;
m_p->set_lng(112.56);
m_p->set_lat(56.78);

msg.set_allocated_pos(m_p);
cout << msg.DebugString() << endl;

③．成员读取

通过成员函数 has_xxx 可以判断 message whether a member of a type is assigned a value.

protoTest::Point* m_p = new  protoTest::Point;
m_p->set_lng(112.56);
m_p->set_lat(56.78);

protoTest::DemoMsg msg; 
msg.set_id(100);
msg.set_allocated_pos(m_p);

if (msg.has_pos())
{
    
    auto& pos = msg.pos();
    cout << pos.lng() << " " << pos.lat();
}

map 类型读写

①．message 示例

message DemoMsg
{
    
   map<int32,string>  a = 1;    
}

②．成员赋值

map Type member assignment must pass mutable_xxx 方法进行：

protoTest::DemoMsg msg; 
msg.mutable_a()->insert({
     1,"aaaaa" });
msg.mutable_a()->insert({
     2,"bbbbb" });
msg.mutable_a()->insert({
     3,"ccccc" });   
cout << msg.DebugString() << endl;

③．成员读取

protoTest::DemoMsg msg; 
msg.mutable_a()->insert({
     1,"aaaaa" });
msg.mutable_a()->insert({
     2,"bbbbb" });   
auto map = msg.mutable_a();
if (map->contains(1))
{
    
    cout << map->at(1) << endl;
}

any 类型读写

①．概述

any Can store serialized data of any known type,Often used for repackaging of struct data,that can combine different types of message packaged in the same message 中进行传输.

②．message 示例

syntax = "proto3";
import "google/protobuf/any.proto";
package protoTest;

message Point
{
    
   double lng = 1;
   double lat = 2;
}
message Node
{
    
   int32 id = 1;
   string name = 2;
}
message DemoMsg
{
    
   int32 id = 1;
   google.protobuf.Any data = 2;
}

③．成员赋值

使用 any 类型的成员函数 PackFrom 来进行赋值.

protoTest::Point m_p;
m_p.set_lng(112.56);
m_p.set_lat(56.78);

protoTest::DemoMsg msg; 
msg.set_id(1);
msg.mutable_data()->PackFrom(m_p);
    
cout << msg.DebugString() << endl;

④．message 类型判断

通过成员函数 Is Can determine whether it is a specified type of data.

protoTest::Point m_p;
m_p.set_lng(112.56);
m_p.set_lat(56.78);

protoTest::Node m_node;
m_node.set_id(1);
m_node.set_name("Zhangsan");

protoTest::DemoMsg msg1; 
msg1.set_id(1);
msg1.mutable_data()->PackFrom(m_p);

protoTest::DemoMsg msg2;
msg2.set_id(2);
msg2.mutable_data()->PackFrom(m_node);

auto checkAny = [&](const protoTest::DemoMsg& msg) {
    
    if (msg.data().Is<protoTest::Point>())
         cout << " msgID:" << msg.id() << " 中 data 类型为 Point " << endl;
    else if( msg.data().Is<protoTest::Node>() )
         cout << " msgID:" << msg.id() << " 中 data 类型为 Node " << endl;
};
    
checkAny(msg1);
checkAny(msg2);

⑤．成员读取

通过成员函数 UnpackTo 可以把 any The data is restored to the corresponding structure data.

protoTest::Point m_p;
m_p.set_lng(112.56);
m_p.set_lat(56.78);

protoTest::DemoMsg msg; 
msg.set_id(1);
msg.mutable_data()->PackFrom(m_p);
  
if (msg.data().Is<protoTest::Point>())
{
    
    protoTest::Point pos;
    if (msg.data().UnpackTo(&pos))
    {
    
        cout << pos.DebugString() << endl;
    }
}

oneof 类型读写

①．概述

oneof 类型同 C++ 中的 union 类型,Only one type is valid at a time.

②．message 示例

message DemoMsg
{
    
   oneof test{
    
     int32 id = 1;
  string name =2;
   };
}

③．成员赋值

直接使用 set_xxx To the appropriate members of the assignment,but only the last assigned data is valid.

protoTest::DemoMsg msg;  
msg.set_id(100);
msg.set_name("123");

cout << msg.DebugString() << endl;

④．数据类型判断

通过 has_xxx Method to determine whether the corresponding type member is assigned a value：

protoTest::DemoMsg msg;  
msg.set_id(100);
msg.set_name("123");

if (msg.has_name())
{
    
    cout << "msg 中为 string 类型" << endl;
}

通过 xxx_case The method currently judges the saved member type：

protoTest::DemoMsg msg;  
msg.set_id(100);
msg.set_name("123");

switch (msg.test_case())
{
    
   case protoTest::DemoMsg::kId:
       cout << "msg 中为 int32 类型" << endl; break;
   case protoTest::DemoMsg::kName:
       cout << "msg 中为 string 类型" << endl; break;
   default:
       break;
}

⑤．成员读取

To determine the current first save the field type,再读取数据.

protoTest::DemoMsg msg;  
msg.set_id(100);
msg.set_name("123");

switch (msg.test_case())
{
    
    case protoTest::DemoMsg::kId:
        cout << msg.id() << endl; break;
    case protoTest::DemoMsg::kName:
        cout << msg.name() << endl; break;
    default:
        break;
 }