How can I put a stl::vector string into the DB and then get it out?

Question

Hello,
As the title, here's a test case with problems,but anyway you can still run it. ( VC6/XP-32/BDB 4.7 )
I know this may be wrong,and I'd like to know how can I do this.
Can someone help me please? I would appreciate it very much.
************ Copy,Compile and Run ***************
#include <iostream>
#include <vector>
#include "db_cxx.h"
int main()
     std::string dbName("database.db");
     u_int32_t db_flags=DB_CREATE;
     Db* db=NULL;
     // Prepare key(int)/data(vector<string>) pair.
     int int_key=2;
     std::vector<std::string> rec_data;
     rec_data.push_back("apple");
     rec_data.push_back("Bob");
     rec_data.push_back("Me");
     // Prepare Dbt for receiving.
     std::vector<std::string> rec_readData;
     Dbt readData;
     readData.set_data(&rec_readData);
     readData.set_ulen(sizeof(rec_readData));
     readData.set_flags(DB_DBT_USERMEM);
     try
          // Open database.
          db = new Db(NULL,0);
          db->open(NULL,dbName.c_str(),NULL,DB_BTREE,db_flags,0);
          // Put
          int ret;
          if(ret=db->put(NULL,new Dbt(&int_key,sizeof(int_key)),new Dbt(&rec_data,sizeof(rec_data)),DB_NOOVERWRITE)==0)
               std::cout<<"put successful!"<<std::endl;
          else { db->err(ret,"Db->put"); }
          // Get
          if(ret=db->get(NULL,new Dbt(&int_key,sizeof(int_key)),&readData,0)==0)
               std::cout<<"get successful!"<<std::endl;
          else { db->err(ret,"Db->get"); }
     catch(DbException &e)
          std::cerr<<"Error: ";
          std::cerr<<e.what()<<std::endl;
     // Close the database
     try
          if(db!=NULL)
               db->close(0);
     catch(DbException &e)
          std::cerr<<"Error closing database: ";
          std::cerr<<e.what()<<std::endl;
     // Display the results.
     // Index out of bounds. <-----
     std::cout << rec_readData[0].c_str();
     std::cout << rec_readData[1].c_str();
     std::cout << rec_readData[2].c_str();
     system("pause");
     // Press any key to go wrong. :(
     return 0;
Regards,
legendsino

Answer 1

You need to convert the std::vector<std::string> into a sequence of bytes. For example, if all strings are shorter than 256 characters, you could create a fresh output string, iterator through the vector, and for each element, append the string length to the output string, followed by the string contents.
Note that ordering in the database will be different from lexicographic order, and you have to keep that in mind when performing range queries.