protobuf C++ SQLite handle blob data - c++

Question

I have a SQLite database which has a table which contains some fields of BLOB type.
What I am trying to do is fetch the field (in fact all other fields too) from the database into C++ send it through protobuf and receive the protobuf .
I have defined the blob fields as bytes in the .proto file
For example
message fields{
...
bytes myBlobField = 1;
}
My c++ file contains
sqlite3_initialize();
rc = sqlite3_open_v2(db_url, &db,SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE,NULL);
std::ostringstream oss;
oss << "select * from attribtable ";
std::string query = oss.str();
rc = sqlite3_prepare_v2(db,query.c_str(),-1,&stmt,NULL
while(sqlite3_step(stmt) == SQLITE_ROW){
sqlite3_column_blob(stmt,10) //This is the blob field
}
How do I store the sqlite3_column_blob(stmt,10) in C++ and how do I set myBlobField using
say reply->set_myblobfield(??)
and receive on the client side using
say receive->get_myblobfield()
So in simple words my question is how do I send the blobfield fetched from database, through protobuf, from server to client in a C++ application?

Answer 1

Using this .proto file
syntax = "proto2";
package prototest;
message fields{
required bytes myBlobField = 1;
}
You initialize the blob using the set_myblobfield() call with the blob pointer and the byte size of the blob which you get from SQLite and then call the SerializeToOstream() method to write it to a stream or to a file.
std::ofstream myoutput("myoutput.bin");
while (sqlite3_step(stmt) == SQLITE_ROW)
{
if (size_t blobSize = sqlite3_column_bytes(stmt, 10))
{
if (const void* blob = sqlite3_column_blob(stmt, 10))
{
prototest::fields myfields;
myfields.set_myblobfield(blob, blobSize);
myfields.SerializeToOstream(&myoutput);
}
}
}