Google protocol buffer messag to byte array C++

Question

I'm currently using two message protocols, one is google proto and the other is c-structs. What is the best solution to convert a google protocol buffer message (MessageLite) to a byte array?

I want, for example, to convert the following google proto message:

message GoogleRequest
{
     optional int32 request = 1 [default = 0];
}

to:

struct Request
{
    int request;
};

I have tried the following but it does not work:

GoogleRequest reqMsg;
reqMsg.set_request(1234);

int size = reqMsg.ByteSize();
Request* reqStruct = new Request;
reqMsg.SerializeToArray((void*)reqStruct , size);

Any suggestions, or is the best way just to do:

reqStruct->request = reqMsg.request();

I have a lot of message types and I would be awesome to find a generic way to do it.

Kenton Varda · Accepted Answer · 2014-08-28 18:21:37Z

15

You say you want to convert your message to a byte array, but your code suggests you're trying to convert it to a C struct (Request). Converting to a C struct is not supported. Converting to a byte array (that is, an array of char) is easy:

int size = reqMsg.ByteSize();
char* array = new char[size];
reqMsg.SerializeToArray(array, size);

Or, another way:

std::string bytes = reqMsg.SerializeAsString();
const char* array = bytes.data();
int size = bytes.size();

However, this array is not a struct, and it could have many different sizes depending on the content. There is no way to convert to a struct except to write code which copies over each field manually.

answered Aug 28, 2014 at 18:21

Kenton Varda

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1 Comment

OleDahle Over a year ago

In 2021, ByteSize has been replaced by ByteSizeLong: warning: ‘int google::protobuf::MessageLite::ByteSize() const’ is deprecated: Please use ByteSizeLong() instead [-Wdeprecated-declarations] Simply change your code to: long size = reqMsg.ByteSizeLong()

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