some snippets that send and receive C++ objects using ROOT streaming capabilities

readwrite_test.cxx

#include "TApplication.h"
#include "TClass.h"
#include "TInterpreter.h"
#include "TBufferFile.h"
#include <utility>
#include <iostream>
#include "StreamMe.h"

/* no streaming is done here, I just write a class to a TBufferFile and try to read it
   with another TBufferFile. */

int main() {
   StreamMe a(123);
   a.b = {1,2,3};

   //get class info
   gInterpreter->ProcessLine("#include \"StreamMe.h\"");
   TClass *c = TClass::GetClass("StreamMe");

   //write class on buffer
   TBufferFile wBuf(TBuffer::kWrite);
   wBuf.WriteObjectAny(&a, c); 

   //read class from buffer
   TBufferFile rBuf(TBuffer::kRead, wBuf.BufferSize(), wBuf.Buffer(), false);
   auto r = (StreamMe*)rBuf.ReadObjectAny(c);

   return 0;
}

streaming_receive.cxx

#include "TSocket.h"
#include "TBufferFile.h"
#include "TInterpreter.h"
#include "TApplication.h"
#include "TClass.h"
#include "StreamMe.h"
#include <iostream>

int main() {
   TApplication app("app", nullptr, nullptr);
   gInterpreter->ProcessLine("#include \"StreamMe.h\"");
   auto c = TClass::GetClass("StreamMe");

   //connect and receive
   TSocket *s = new TSocket("localhost", 9090);
   void *lengthBuf = malloc(1024);
   std::cout << "received " << s->RecvRaw(lengthBuf, sizeof(ULong_t)) << " bytes" << std::endl;
   TBufferFile rBuf(TBuffer::kRead, sizeof(ULong_t), lengthBuf);
   ULong_t classBufSize;
   rBuf.ReadULong(classBufSize);
   std::cout << "classBufSize " << classBufSize << std::endl;
   void *classBuf = malloc(classBufSize);
   std::cout << "received " << s->RecvRaw(classBuf, classBufSize) << " bytes" << std::endl;
   TBufferFile rBuf2(TBuffer::kRead, classBufSize, classBuf);
   auto r = (StreamMe*)rBuf2.ReadObjectAny(c);
   if(!r)
      std::cout << "ERROR; object == nullptr";
   else {
      std::cout << r->a << std::endl;
      std::cout << r->b.front() << std::endl;
      std::cout << r->b.back() << std::endl;
   }
   return 0;
}

streaming_send.cxx

#include "TSocket.h"
#include "TServerSocket.h"
#include "TBufferFile.h"
#include "TInterpreter.h"
#include "TApplication.h"
#include "TClass.h"
#include "StreamMe.h"
#include <iostream>

int main() {
   TApplication app("app", nullptr, nullptr);
   gInterpreter->ProcessLine("#include \"StreamMe.h\"");

   //connect
   TServerSocket ss(9090, kTRUE);
   TSocket *s = ss.Accept();

   //send object
   StreamMe a(123);
   for(unsigned i=0; i<2000; ++i)
      a.b.push_back(i);
   TClass *c = TClass::GetClass("StreamMe");
   TBufferFile classBuf(TBuffer::kWrite);
   classBuf.WriteObjectAny(&a, c);
   TBufferFile wBuf(TBuffer::kWrite);
   wBuf.WriteULong(classBuf.BufferSize());
   wBuf.WriteBuf(classBuf.Buffer(), classBuf.BufferSize());
   std::cout << "sending " << s->SendRaw(wBuf.Buffer(), wBuf.BufferSize()) << " bytes" << std::endl;
   return 0;
}

StreamMe.h

#ifndef _STREAMME_
#define _STREAMME_

struct StreamMe {
   explicit StreamMe(int _a) : a(_a) {};
   StreamMe() : StreamMe(1) {};
   
   int a;
   std::vector<int> b;
};

#endif