using std::map<int , std::string> with Google Protocol Buffer

Question

I wanted to know if it was possible to use a map with a google protocol buffer. I currently have something like this in my .proto file

message MsgA
{
required string symbol = 1 ;
optional int32  freq = 2   [default = 0]; 
}

message MsgB
{

   //What should I do to make a map<int,MsgA>
}

My question is in MsgB i would like to create a type that would be a map:: Any suggestion on how I could accomplish this ?

David Schwartz · Accepted Answer · 2013-07-14 10:58:50Z

2

Do this:

message MapEntry
{
    required int32 mapKey  = 1;
    required MsgA mapValue = 2;
}

message MsgB
{
    repeated MapEntry = 1;
}

You will have to write your own code to convert the map to and from a MsgB, but that should be basically trivial.

answered Jul 14, 2013 at 10:58

David Schwartz

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6 Comments

MistyD Over a year ago

Thanks for your reply. I am thinking about replacing the map with a vector. For this I will use the repeated field. Which I believe would act like a vector. Could you tell me how I can add items to a repeated field in C++

David Schwartz Over a year ago

@MistyD: Use MapEntry& newMapEntry = myMsgB.add_mapentry();. Then fill out the fields in newMapEntry, which is now a reference to a newly-added map entry in message b.

MistyD Over a year ago

I was looking at that in developers.google.com/protocol-buffers/docs/cpptutorial. Isnt it suppose to be MapEntry* newMapEntry = myMsgB.add_mapentry(); ? A pointer instead of a reference ?

MistyD Over a year ago

Since it using reference i wanted to know how we reclaim the memory and when is it safe to delete the pointer ?

David Schwartz Over a year ago

Sorry, you can do it that way. I meant MapEntry& newMapEntry = *myMsgB.add_mapentry();.

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