--- title: "__declspec" ms.date: "03/21/2019" f1_keywords: ["__declspec_cpp", "__declspec", "_declspec"] helpviewer_keywords: ["__declspec keyword [C++]"] --- # __declspec **Microsoft Specific** The extended attribute syntax for specifying storage-class information uses the **__declspec** keyword, which specifies that an instance of a given type is to be stored with a Microsoft-specific storage-class attribute listed below. Examples of other storage-class modifiers include the **static** and **extern** keywords. However, these keywords are part of the ANSI specification of the C and C++ languages, and as such are not covered by extended attribute syntax. The extended attribute syntax simplifies and standardizes Microsoft-specific extensions to the C and C++ languages. ## Grammar *decl-specifier*:
    **__declspec (** *extended-decl-modifier-seq* **)** *extended-decl-modifier-seq*:
    *extended-decl-modifier*_opt
    *extended-decl-modifier* *extended-decl-modifier-seq* *extended-decl-modifier*:
    **align(** *#* **)**
    **allocate("** *segname* **")**
    **allocator**
    **appdomain**
    **code_seg("** *segname* **")**
    **deprecated**
    **dllimport**
    **dllexport**
    **jitintrinsic**
    **naked**
    **noalias**
    **noinline**
    **noreturn**
    **nothrow**
    **novtable**
    **process**
    **property(** { **get=**_get_func_name_ | **,put=**_put_func_name_ } **)**
    **restrict**
    **safebuffers**
    **selectany**
    **spectre(nomitigation)**
    **thread**
    **uuid("** *ComObjectGUID* **")** White space separates the declaration modifier sequence. Examples appear in later sections. Extended attribute grammar supports these Microsoft-specific storage-class attributes: [align](../cpp/align-cpp.md), [allocate](../cpp/allocate.md), [allocator](../cpp/allocator.md), [appdomain](../cpp/appdomain.md), [code_seg](../cpp/code-seg-declspec.md), [deprecated](../cpp/deprecated-cpp.md), [dllexport](../cpp/dllexport-dllimport.md), [dllimport](../cpp/dllexport-dllimport.md), [jitintrinsic](../cpp/jitintrinsic.md), [naked](../cpp/naked-cpp.md), [noalias](../cpp/noalias.md), [noinline](../cpp/noinline.md), [noreturn](../cpp/noreturn.md), [nothrow](../cpp/nothrow-cpp.md), [novtable](../cpp/novtable.md), [process](../cpp/process.md), [restrict](../cpp/restrict.md), [safebuffers](../cpp/safebuffers.md), [selectany](../cpp/selectany.md), [spectre](../cpp/spectre.md), and [thread](../cpp/thread.md). It also supports these COM-object attributes: [property](../cpp/property-cpp.md) and [uuid](../cpp/uuid-cpp.md). The **code_seg**, **dllexport**, **dllimport**, **naked**, **noalias**, **nothrow**, **property**, **restrict**, **selectany**, **thread**, and **uuid** storage-class attributes are properties only of the declaration of the object or function to which they are applied. The **thread** attribute affects data and objects only. The **naked** and **spectre** attributes affect functions only. The **dllimport** and **dllexport** attributes affect functions, data, and objects. The **property**, **selectany**, and **uuid** attributes affect COM objects. For compatibility with previous versions, **_declspec** is a synonym for **__declspec** unless compiler option [/Za \(Disable language extensions)](../build/reference/za-ze-disable-language-extensions.md) is specified. The **__declspec** keywords should be placed at the beginning of a simple declaration. The compiler ignores, without warning, any **__declspec** keywords placed after * or & and in front of the variable identifier in a declaration. A **__declspec** attribute specified in the beginning of a user-defined type declaration applies to the variable of that type. For example: ```cpp __declspec(dllimport) class X {} varX; ``` In this case, the attribute applies to `varX`. A **__declspec** attribute placed after the **class** or **struct** keyword applies to the user-defined type. For example: ```cpp class __declspec(dllimport) X {}; ``` In this case, the attribute applies to `X`. The general guideline for using the **__declspec** attribute for simple declarations is as follows: *decl-specifier-seq* *init-declarator-list*; The *decl-specifier-seq* should contain, among other things, a base type (e.g. **int**, **float**, a **typedef**, or a class name), a storage class (e.g. **static**, **extern**), or the **__declspec** extension. The *init-declarator-list* should contain, among other things, the pointer part of declarations. For example: ```cpp __declspec(selectany) int * pi1 = 0; //Recommended, selectany & int both part of decl-specifier int __declspec(selectany) * pi2 = 0; //OK, selectany & int both part of decl-specifier int * __declspec(selectany) pi3 = 0; //ERROR, selectany is not part of a declarator ``` The following code declares an integer thread local variable and initializes it with a value: ```cpp // Example of the __declspec keyword __declspec( thread ) int tls_i = 1; ``` **END Microsoft Specific** ## See also [Keywords](../cpp/keywords-cpp.md)
[C Extended Storage-Class Attributes](../c-language/c-extended-storage-class-attributes.md)