How Can I Properly Split a C Templated Class Between Header and Source Files?

Common Pitfalls in Splitting C Template Classes

When attempting to split a templated C class into .hpp and .cpp files, you may encounter compilation errors due to missing symbol definitions. This can be particularly frustrating for those familiar with the practice of separating header and implementation files.

Understanding the Issue

The compilation process differs between header files and .cpp files. Header files are preprocessed, while .cpp files are actually compiled. This means that template class definitions must be fully available to the compiler at the time of compilation, which is not possible if they are split into separate files.

The compiler needs to determine the data type of the template to create an appropriate memory layout for the object. This information is unavailable if the method definitions are located in a separate cpp file. Consequently, the compiler is unable to generate instructions for the method definitions, and the 'this' pointer cannot be fully defined.

Possible Solutions

Combining All Code in .hpp File:

The only reasonable solution is to move all the code from the .cpp file into the .hpp file. This removes the issue of missing symbols but presents an organizational headache.

Alternative Approach: Separating Data Structures from Algorithms

Instead of splitting the template class, consider separating the data structures from the algorithms. The template class should solely represent the data structure, with non-templatized algorithm classes handling operations on the data. This allows for greater flexibility and modularity while preserving the ability to hide implementation details in separately compiled binary files.

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