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protobuf tutorial

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Series

Guide

intro

如果proto结构体的变量是基础变量，比如int、string等等，那么set的时候直接调用set_xxx即可。
如果变量是自定义类型，那么C++的生成代码中，就没有set_xxx函数名，取而代之的是三个函数名：

  • set_allocated_xxx() 传入参数必须是new出来的指针,protobuf内部会自动释放
  • release_xxx()
  • mutable_xxx() 在mutable_xxx()函数内部new一个对象并返回对象地址，后续可以赋值

user-defined field

protobuf

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syntax = "proto2";

package kezunlin.proto;

message Vector3D{
  optional float x = 1;
  optional float y = 2;
  optional float z = 3;
}

message PlayerPos{
  optional uint32 id = 1;
  optional Vector3D pos = 2;
}

demo.pb.h

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// optional uint32 id = 1;
  bool has_id() const;
  void clear_id();
  static const int kIdFieldNumber = 1;
  ::google::protobuf::uint32 id() const;
  void set_id(::google::protobuf::uint32 value);
  
// optional .kezunlin.proto.Vector3D pos = 2;
  bool has_pos() const;
  void clear_pos();
  static const int kPosFieldNumber = 2;
  public:
  const ::kezunlin::proto::Vector3D& pos() const;
  ::kezunlin::proto::Vector3D* release_pos();
  ::kezunlin::proto::Vector3D* mutable_pos();
  void set_allocated_pos(::kezunlin::proto::Vector3D* pos);

基础类型字段id通过id()和set_id()操作;
自定义类型字段pos通过pos(),set_allocated_pos（）,release_pos（）,mutable_pos()操作；

usage

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PlayerPos player;
player.set_id(100);

// method 1
Vector3D *pos = new Vector3D();
pos->x = 1;
pos->y = 2;
pos->z = 3;
player.set_allocated_pos(pos);

// method 2 
Vector3D *pos = player.mutable_pos();
pos->x = 1;
pos->y = 2;
pos->z = 3;

总结：对于自定义类型

  • 使用set_allocated_xxx，赋值的对象需要new出来，不能用局部的，这里保存的是对象的指针。
  • 使用mutable_xxx，赋值时候，可以使用局部变量，因为在调用的时，内部做了new操作。

repeated field

protobuf

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syntax = "proto2";

package kezunlin.proto;

message LidarPoint {
  optional double x = 1;  // in meters.
  optional double y = 2;  // in meters.
  optional double z = 3;  // height in meters.
  optional double intensity = 4; // lidar intensity
}

message PointCloud {
  optional uint64 timestamp_msec = 1;  // Header
  repeated LidarPoint points = 2; // lidar point cloud
}

point_cloud.pb.h

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// repeated .kezunlin.proto.LidarPoint points = 2;
  int points_size() const;
  void clear_points();
  static const int kPointsFieldNumber = 2;
  ::kezunlin::proto::LidarPoint* mutable_points(int index);
  ::google::protobuf::RepeatedPtrField< ::kezunlin::proto::LidarPoint >*
      mutable_points();
  const ::kezunlin::proto::LidarPoint& points(int index) const;
  ::kezunlin::proto::LidarPoint* add_points();
  const ::google::protobuf::RepeatedPtrField< ::kezunlin::proto::LidarPoint >&
      points() const;

usage

使用add_xxx来新建对象

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kezunlin::proto::PointCloud pc;

LidarPoint* pt = pc.add_points();
pt->set_x(1);
pt->set_y(2);
pt->set_z(3);
pt->set_intensity(1);

Reference

History

  • 20190117: created.