Why Must Template Class Definitions Be Included in Header Files?

Including Template Class Definitions in Header Files: A Necessity

The question arises as to why the implementation and declaration of a template class are required to reside within the same header file. To address this, it is crucial to understand that a compiler requires access to the entire template definition, beyond just its signature, to generate code for each instantiation of the template. Consequently, the function definitions must be moved to the header.

The Inclusion Model provides a comprehensive explanation of this requirement. In essence, when a template class is instantiated, the compiler generates specialized code for that particular instantiation. To achieve this, the compiler needs to have a complete understanding of the template structure, including its member function definitions. By locating both the declaration and implementation within the same header file, the compiler can efficiently access all necessary information during code generation.

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