If you have ever used Data Access Objects (DAO) both in Visual Basic and Visual C++ with MFC, you must have noticed that in Visual Basic, manipulating Microsoft Access MDB files is a more enjoyable way of spending time than doing it in Visual C++ with MFC. And, you must have thought whether a workaround exists to make working with MDB in Visual C++ as flexible as in Visual Basic.
To solve this problem, let's try to use in Visual C++ the same mechanism as is used in Visual Basic. This mechanism assumes that you should work directly with type libraries. Unlike Visual Basic, which is more adapted for rapid application development and has its own methods for accessing type libraries, in Visual C++, working with type libraries is more preferable through converting the content of the type library into C++ classes with the
The best way to understand this is by reading a sample source:
// Describe the full path to dao360.dll file. Interface files dao360.tlh and
// dao360.tli will be generated automatically during compilation.
// The #import directive creates "DAO" namespace to avoid name conflicts with
// other libraries. So, all DAO members must be referenced with "DAO::" prefix,
// e.g. DAO::DBEngine
#import <C:\Program Files\Common Files\Microsoft Shared\DAO\dao360.dll>
#include <span class="code-keyword"><stdio.h></span>
Compile this example in the command line as:
cl -GX daocpp.cpp
and run daocpp.exe. The database file test.mdb will be created. This file will contain the table Test with one record of data.
As you can see, the types
Database are mapped to the
DAO::DatabasePtr C++ classes after incorporating information from the type library. The type
TableDef will be mapped to
Note: Using DAO requires converting C++ types to the variant type. In this sample, you can see that the C++ type
long is converted to the type
_variant_t vI = _variant_t((long) i);
In the same way, for example, the logical values
False of the
bool type will be converted to the type
_variant_t vTrue = _variant_t((bool) -1);
_variant_t vFalse = _variant_t((bool) 0);
I hope this short article will help you to write more efficient code in your applications.