title	Microsoft-Specific Modifiers | Microsoft Docs
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Microsoft-Specific Modifiers

This section describes Microsoft-specific extensions to C++ in the following areas:

• Based addressing, the practice of using a pointer as a base from which other pointers can be offset

• Function calling conventions

• Extended storage-class attributes declared with the __declspec keyword

• The __w64 keyword

Many of the Microsoft-specific keywords can be used to modify declarators to form derived types. For more information about declarators, see Declarators.

Microsoft-Specific Keywords

Keyword	Meaning	Used to Form Derived Types?
__based	The name that follows declares a 32-bit offset to the 32-bit base contained in the declaration.	Yes
__cdecl	The name that follows uses the C naming and calling conventions.	Yes
__declspec	The name that follows specifies a Microsoft-specific storage-class attribute.	No
__fastcall	The name that follows declares a function that uses registers, when available, instead of the stack for argument passing.	Yes
__restrict	Similar to __declspec(restrict), but for use on variables.	No
__stdcall	The name that follows specifies a function that observes the standard calling convention.	Yes
__w64	Marks a data type as being larger on a 64-bit compiler.	No
__unaligned	Specifies that a pointer to a type or other data is not aligned..	No
__vectorcall	The name that follows declares a function that uses registers, including SSE registers, when available, instead of the stack for argument passing.	Yes

See Also

C++ Language Reference