How Can I Effectively Handle `dllexport`/`dllimport` in Shared Libraries Without Relying on `COMPILING_DLL`?

Macro for dllexport/dllimport Switch

When working with shared libraries on Windows, defining the appropriate macros for exporting and importing functions becomes necessary. The traditional approach involves using the COMPILING_DLL macro.

Defining COMPILING_DLL

The COMPILING_DLL macro is typically not explicitly defined and relies on the default behavior of Visual Studio. By default, it is considered defined when building a DLL project and undefined when using the DLL in a client application. However, this approach can lead to issues when using load-time dynamic linking (LTDL), where you cannot use the same header for both scenarios.

Alternative Solution

One alternative to using COMPILING_DLL is to employ a default macro defined locally to the project. By default, Visual Studio defines macros like MYDLL_EXPORTS and MYDLL_IMPORTS for the current project. These macros can be used as follows:

#ifdef  MYDLL_EXPORTS 
    /*Enabled as "export" while compiling the dll project*/
    #define DLLEXPORT __declspec(dllexport)  
#else
    /*Enabled as "import" in the Client side for using already created dll file*/
    #define DLLEXPORT __declspec(dllimport)  
#endif

In this example, where the project name is "MyDLL," the macro MYDLL_EXPORTS would be defined when building the DLL project and undefined when using it externally. By leveraging these default macros, you can define the DLLEXPORT macro appropriately for both scenarios without relying on the existence of COMPILING_DLL.

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