These attributes explicitly define the DLL's interface to its client, which can be the executable file or another DLL. Declaring functions as dllexport eliminates the need for a module-definition (.DEF) file, at least with respect to the specification of exported functions. Note that dllexport replaces the __export keyword.

If a class is marked declspec(dllexport), any specializations of class templates in the class hierarchy are implicitly marked as declspec(dllexport). This means templates are explicitly instantiated and its members must be defined.

dllexport of a C++ function will expose the function with C++ name mangling. If C++ name mangling is not desired, either use a .def file (EXPORTS keyword) or declare the function as extern "C".

The declaration of dllexport and dllimport must use extended attribute syntax and the __declspec keyword.

// Example of the dllimport and dllexport class attributes
__declspec( dllimport ) int i;
__declspec( dllexport ) void func();

Alternately, to make your code more readable, you can use macro definitions:

#define DllImport   __declspec( dllimport )
#define DllExport   __declspec( dllexport )

DllExport void func();
DllExport int i = 10;
DllImport int j;
DllExport int n;

For additional information, see:

• Definitions and Declarations

• Defining Inline C++ Functions with dllexport and dllimport

• General Rules and Limitations

• Using dllimport and dllexport in C++ Classes

END Microsoft Specific

Concepts