Efficient Memory Use Adding Buffer Output To Hash Table C++

This code fully works, but wonder if there is a more efficient way to write this code.

Some points:

• RetrieveData is 3rd party API that takes 3 parameters - pointer to buffer containing the data, number of bytes to retrieve, actual number of bytes to retrieve
• The buffer returned from retrieve data is non-null terminated unicode string
• 99% of the time buffer is <256 bytes in size, but larger size is possible and needs to be handled

• Reason adding data to map is later the "ID" must be retrieved based on string data

  std::map<std::wstring, unsigned int> map_columns;
  do 
  {
          unsigned int id;
          unsigned long pcbActual;
          char * data;
          {
              RetrieveID(&id);
              // RetrieveData ( <pointer to buffer for data>, <amount of bytes to retrieve>, <output actual bytes of data>)
              // find out how large buffer we need to retrieve data
              RetrieveData(NULL, 0, &pcbActual);
              data = new char[pcbActual + 2];
              // actually retrieve data
              RetrieveData(data, pcbActual, &pcbActual);
              // add null terminator to returned string
              data[pcbActual] = '\0';
              data[pcbActual + 1] = '\0';
              std::wstring str((wchar_t*)data);
              map_columns[str] = id;
          }
      } while (MoveNext());