Why Can't I Separate Templated C Class Implementations into Header and Source Files?

Splitting Templated C Classes into Header (.hpp) and Source (.cpp) Files: Exploring the Constraints

Templated C classes pose a unique challenge when it comes to splitting them into header (.hpp) and source (.cpp) files. This approach may seem intuitive, but it encounters compilation errors when the implementation is housed in a separate .cpp file.

Why is This Split Not Feasible?

Unlike non-templated classes, template classes are not fully defined in the header file. Instead, the compiler generates a separate class definition for each instantiation of the template. This process requires knowledge of the actual data type used in the instantiation, which is not available when the implementation is in a separate .cpp file.

Consequence: Undefined Symbols

As a result, the linker cannot find the symbols defined in the .cpp file, leading to undefined reference errors. Compiling the .cpp file as an independent object file does not resolve the issue, as the necessary class information is not included in the resulting object.

Alternative Approach: Data Structures and Algorithms Separation

To address this limitation, it is recommended to separate the data structures and algorithms in templated classes. By defining only the data structures in the template class header, you can hide implementation details in separate non-templated class libraries that utilize or work on the template classes.

Conclusion

While it may be tempting to split templated C classes into .hpp and .cpp files, this approach faces insurmountable compilation challenges. The only practical solution is to design templated classes to represent data structures rather than algorithms, allowing for the separation of implementation details in non-templated class libraries.

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