Identify the Error

• The error occurs because 'dllimport' is being used incorrectly. The 'dllimport' specifier is used to declare a function or variable that is implemented in a DLL. It should not be used in the definition of a function.
• Review the error message and identify where your code is trying to define a function that has been incorrectly marked with 'dllimport'.

Review Your Export/Import Macros

• Check whether your code uses any macro to define 'dllimport'/'dllexport' qualifiers. Usually, this involves macros that look like MY_API or MY_DLL\_SPEC.
• Ensure these macros are correctly defined based on whether you are building the DLL or using the DLL. For example:

  ```cpp
  #ifdef BUILDING_MY_DLL
  #define MY_API __declspec(dllexport)
  #else
  #define MY_API __declspec(dllimport)
  #endif
  ```
  

• If mistakenly applying 'dllimport' on definition, remove it or apply 'dllexport' instead if you are building the DLL.

Correct the Function Declaration/Definition

• For functions imported from a DLL, only use 'dllimport' when declaring the function in the consuming code. If you have a function definition like:

  ```cpp
  __declspec(dllimport) void function();
  ```

  Change it to:

  ```cpp
  void function();
  ```
  When you define it in your source/implementation file.
  

• If you're defining this function in a DLL you're building, it should be exported. Use the 'dllexport' attribute only during definition:

  ```cpp
  #ifdef BUILDING_MY_DLL
  __declspec(dllexport)
  #else
  __declspec(dllimport)
  #endif
  void function();
  ```

  Meanwhile, in your implementation:

  ```cpp
  void function() {
  // Function implementation
  }
  ```
  

Re-verify the Build Configuration

• Ensure that your project build settings or compiler flags correctly define any macros used to distinguish between building and consuming the DLL. These settings control how 'BUILDING_MY_DLL' or similar macros are set in the build process.
• If using CMake or another build system, check how the compiler definitions are provided. Adjust them using commands like `target_compile_definitions` for CMake:

```cmake
target_compile_definitions(my_target PRIVATE BUILDING_MY_DLL)
```

Test and Validate

• After making the necessary adjustments, rebuild the project and test it thoroughly to confirm that the 'dllimport' and 'dllexport' are applied correctly.
• Use a linker or dependency walker tool to check the import/export tables of your DLL for any discrepancies.

Consider Compiler/Platform-Specific Behaviors

• Remember that '\_\_declspec' qualifiers are specific to MSVC (Microsoft Visual C++). If planning to scale to other platforms or compilers (e.g., GCC, Clang), you might want to use a more portable approach.
• Evaluate using C++11 attribute syntax or compiler-specific attributes like **attribute** in GCC to ensure portability:

```cpp
#ifdef _WIN32

define DLL_PUBLIC __declspec(dllexport)

#else

define DLL_PUBLIC attribute((visibility("default")))

#endif
```