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.
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.
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.
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.
In some cases, you may be able to disable warnings for STL objects if the following conditions are met:
However, it's important to exercise caution and ensure that no assignment operators, copy constructors, etc. are inlined into the DLL client.
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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