protocol buffer

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

compilation:
for .proto file:
protoc -I=$SRC_DIR –cpp_out=$DST_DIR $SRC_DIR/addressbook.proto

for .cpp file:

#include “…pb.h”
g++ tutorial/readAddressbook.cpp tutorial/addressbook.pb.cc -o ./tutorial/read -lprotobuf

proto.buffer

package .. => namespace
message .. => class in the namespace
some const and enum, basic function

.pb.h file

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// in proto file
package tutorial
message Person {
    ....
    // declare field:`field_type field_name` 
    // eg. id, email, phone, name
    ......

    message PhoneNumber
}

message AddressBook{
    Person ..name_of_variable
}

// in proto.h file
namespace tutorial{
    
    // declare some methods and variables, and class

    
    class AddressBook
    class Person
    class Person_PhoneNumber

    // definition:
    class Person{
      public:
        ....
        // implements message --------

        /** standard message methods:
        * check or manipulate the entire msg
        **/
        bool IsInitialized() const; // checks if all required field is set

        string DebugString() const; // return useful msg for debug

        void CopyFrom(const Person& from); // overwrites the message with the given message's values.

        void Clear();: clears all the elements back to the empty state.
            
        // nested types ----------
         typedef ...

        // accesssors ----- methods for each field of msg Person declared in .proto file

        // required int32 id = 2
        # id
        inline bool has_id() const;
        inline void clear_id();
        static const int kIdFieldNumber = 2; // id
        inline int32_t id() const;
        inline void set_id(int32_t value); 
        // type int only have the most basic method:`has_`, `clear_`, `set_`

        // required string email = 3
        # email: methods for email: `has_`, `clear_`, `set_`, mutable
        inline bool has_email() const;
        inline void clear_email();
        static const int kEmailFieldNumber = 3;
        inline const ::std::string& email() const;
        inline void set_email(const ::std::string& value);
        inline void set_email(const char* value);
        inline ::std::string* mutable_email(); // spetial method for `string`

        // define in subMsg `PhoneNumber` repreated ? phone = 4;
        // repeated .tutotial.Person.PhoneNumber phone = 4;
        # phone: methods for phone: size
        // _size, clear_, id method:
        inline int phone_size() const; // spetial method for `repeated`
        inline void clear_phone();
        static const int kPhoneFieldNumber = 4;
        // constructor 
        inline const ::google::protobuf::RepeatedPtrField< ::tutorial::Person_PhoneNumber >& phone() const;
        // mutable_, add_
        inline ::google::protobuf::RepeatedPtrField< ::tutorial::Person_PhoneNumber >* mutable_phone();
        inline const ::tutorial::Person_PhoneNumber& phone(int index) const;
        inline ::tutorial::Person_PhoneNumber* mutable_phone(int index);
        inline ::tutorial::Person_PhoneNumber* add_phone();
        }

      private:
       ....
       // end class
}

.cpp file

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#include "addressbook.pb.h"

int main(){
    // initial
    tutrorial::AddressBook address_book;
    // class AddressBook have field person, type: msg Person
    // therefore have method: `add_person`
    PromptForAddress(address_book.add_person())

    // address_book.add_person() is a pointer to object of class Person
}

void PromptForAddress(tutorial::Person* person){
    person->set_id(2);
    tutorial::Person::PhoneNumber* phone_number = person->add_phone();
    phone_number->set_number(number);
    phone_number->set_type(tutorial::Person::MOBILE);

}