Active Template Library
Windows development library
From Wikipedia, the free encyclopedia
The Active Template Library (ATL) is a set of template-based C++ classes developed by Microsoft, intended to simplify the programming of Component Object Model (COM) objects. The COM support in Microsoft Visual C++ allows developers to create a variety of COM objects, OLE Automation servers, and ActiveX controls.[1][2] ATL includes an object wizard that sets up primary structure of the objects quickly with a minimum of hand coding. On the COM client side ATL provides smart pointers that deal with COM reference counting. The library makes heavy use of the curiously recurring template pattern.
| Active Template Library | |
|---|---|
| Developer | Microsoft |
| Written in | C++ |
| Operating system | Microsoft Windows |
| Type | Library or framework |
| License | Proprietary |
History
COM objects can also be created with Microsoft Foundation Classes (MFC), but this leads to larger binaries that require support DLLs.[3] ATL, on the other hand, is a more lightweight alternative in situations where the graphical user interface parts of MFC are not required.[4]
Older versions of ATL (ATL prior to version 7.1, pre-Visual Studio 2005) are incompatible with DEP because it places executable thunks in data heap.[5][6][7] This problem can be mitigated with DEP-ATL thunk emulation with performance penalty.[8][9]
In ATL version 7 (Visual Studio 2003), which directly succeeded version 3 (Visual Studio 6.0), a number of MFC classes like CString were made available in ATL, or more precisely moved to an ATLMFC common layer which is shared by both libraries. ATL version 7 also introduced attributes in C++ in an attempt to provide something similar to CLI attributes, however these have not been particularly successful, and have been deemphasized in ATL version 8 (Visual Studio 2005); the various wizards no longer generate them by default. Version 7 also introduced new string conversion classes.
On July 28, 2009, Microsoft released a patch to ATL to fix a bug that could allow ActiveX controls created using ATL to be vulnerable to a remote code execution security flaw.[10]
Since Visual Studio 2013 (ATL version 12), all ATL code is static, eliminating the DLL.[11][12]
ATL version is defined by ATL_VER macros and can be queried via AtlGetVersion() function.[13]
Support classes
Compiler COM support
Although not formally part of ATL, Microsoft Visual C++ also includes additional C++ RAII classes to simplify management of COM types. These compiler COM support classes can be used as replacement for or in combination with ATL, and includes:
_com_ptr_t[18] smart-pointer that decorates the COM interface name with a "Ptr" suffix,_bstr_t[19] BSTR wrapper,_variant_t[20] VARIANT wrapper, and_com_error[21] HRESULT wrapper.
Note that as of Visual Studio 2012, the compiler COM support classes does not include a SAFEARRAY wrapper.