Does Forward Declaring with DLL_EXPORT Truly Solve the DLL Interface Issue for Exported STL Objects?

Does Forward Declaring with DLL_EXPORT Solve the Problem for Exported STL Objects?

When attempting to export classes containing STL objects, such as std::vector and std::string, from a DLL, you may encounter warnings indicating that the members of these objects lack a "dll-interface." While forward declaring the affected members with DLL_EXPORT can suppress some of these warnings, it's important to understand the implications and consider potential alternatives.

DLL-Interface for STL Objects

When exporting classes with complex members like STL containers, it's essential to provide a DLL-interface. This ensures that the compiler creates the necessary functions within the DLL itself, making them accessible to clients.

Consequences of Forward Declaring with DLL_EXPORT

Forward declaring the members with DLL_EXPORT does not fully address the problem. It merely injects the DLL_EXPORT keyword at the point of compilation, but this does not export the methods of the STL objects.

Addressing the Issue Properly

To resolve the issue, you should mark the STL classes used by the members as DLL_EXPORT in their compilation units. This ensures that the methods of these classes are properly exported.

Conditions for Disabling Warnings

In some cases, you may be able to disable warnings for STL objects if the following conditions are met:

• The clients and the DLL are built using the same libraries and compilers.
• The STL classes are header-only.

However, it's important to exercise caution and ensure that no assignment operators, copy constructors, etc. are inlined into the DLL client.

Choosing the Right Approach

Whether or not to design a DLL interface using STL objects depends on several factors. If a high-level interface is required, a static library may be a more suitable option.

Ultimately, the best approach depends on the specific requirements and architecture of your application. Consider the potential implications and make an informed decision based on your needs.

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