Visual Basic for Applications VBA is an implementation of Microsoft's event-driven programming language Visual Basic 6, which was declared legacy in 2008, and its associated integrated development environment IDE. Although pre-.NET Visual Basic is no longer supported or updated by Microsoft, the VBA programming language was upgraded in 2010 with the introduction of Visual Basic for Applications 7 in Microsoft Office applications.
Visual Basic for Applications enables building user-defined functions UDFs, automating processes and accessing Windows API and other low-level functionality through dynamic-link libraries DLLs. It supersedes and expands on the abilities of earlier application-specific macro programming languages such as Word's WordBASIC. It can be used to control many aspects of the host application, including manipulating user interface features, such as menus and toolbars, and working with custom user forms or dialog boxes.
As its name suggests, VBA is closely related to Visual Basic and uses the Visual Basic Runtime Library. However, VBA code normally can only run within a host application, rather than as a standalone program. VBA can, however, control one application from another using OLE Automation. For example, VBA can automatically create a Microsoft Word report from Microsoft Excel data that Excel collects automatically from polled sensors. VBA can use, but not create, ActiveX/COM DLLs, and later versions add support for class modules.
VBA is built into most Microsoft Office applications, including Office for Mac OS X except version 2008, and other Microsoft applications, including Microsoft MapPoint and Microsoft Visio. VBA is also implemented, at least partially, in applications published by companies other than Microsoft, including ArcGIS, AutoCAD, CorelDraw, LibreOffice, Reflection, SolidWorks,, WordPerfect, and UNICOM System_Architect which supports VBA 7.1.
Code written in VBA is compiled to Microsoft P-Code pseudo-code, a proprietary intermediate language, which the host applications Access, Excel, Word, Outlook, and PowerPoint store as a separate stream in COM Structured Storage files e.g.,
.xls independent of the document streams. The intermediate code is then executed by a virtual machine hosted by the host application. Despite its resemblance to many old BASIC dialects particularly Microsoft BASIC, from which it is indirectly derived, VBA is incompatible with any of them except Visual Basic, where source code of VBA modules and classes can be directly imported, and which shares the same library and virtual machine. Compatibility ends with Visual Basic version 6; VBA is incompatible with Visual Basic .NET VB.NET. VBA is proprietary to Microsoft and, apart from the COM interface, is not an open standard.
Interaction with the host application uses OLE Automation. Typically, the host application provides a type library and application programming interface API documentation which document how VBA programs can interact with the application. This documentation can be examined from inside the VBA development environment using its Object Browser.
Visual Basic for Applications programs which are written to use the OLE Automation interface of one application cannot be used to automate a different application, even if that application hosts the Visual Basic runtime, because the OLE Automation interfaces will be different. For example, a VBA program written to automate Microsoft Word cannot be used with a different word processor, even if that word processor hosts VBA.
Conversely, multiple applications can be automated from the one host by creating Application objects within the VBA code. References to the different libraries must be created within the VBA client before any of the methods, objects, etc. become available to use in the application. This is achieved through what is referred to as Early or Late Binding. These application objects create the OLE link to the application when they are first created. Commands to the different applications must be done explicitly through these application objects in order to work correctly.
As an example, VBA code written in Microsoft Access can establish references to the Excel, Word and Outlook libraries; this allows creating an application that --- for instance --- runs a query in Access, exports the results to Excel and analyzes them, and then formats the output as tables in a Word document or sends them as an Outlook email.
VBA programs can be attached to a menu button, a macro, a keyboard shortcut, or an OLE/COM event, such as the opening of a document in the application. The language provides a user interface in the form of UserForms, which can host ActiveX controls for added functionality.
Inter-process communication automation includes the Dynamic Data Exchange DDE and RealTimeData RTD which allows calling a Component Object Model COM automation server for dynamic or realtime financial or scientific data.
As with any common programming language, VBA macros can be created with malicious intent. Using VBA, most of the security features lie in the hands of the user, not the author. The VBA host application options are accessible to the user. The user who runs any document containing VBA macros can preset the software with user preferences. End-users can protect themselves from attack by disabling macros from running in an application or by granting permission for a document to run VBA code only if they are sure that the source of the document can be trusted.