Why Does My C Code Produce an 'Undefined Reference to Template Class Constructor' Error?

Undefined Reference to Template Class Constructor

In this C code, the compiler generates the error "undefined reference to cola(float)::cola()". This error occurs because the compiler cannot find the implementation of the constructor for the template class cola.

Answer 1: Explicit Template Instantiation

One solution is to explicitly instantiate the template class cola at the end of cola.cpp, forcing it to compile the concrete instantiations.

template class cola<float>;
template class cola<string>;

Answer 2: Header File Inclusion

Alternatively, the implementation of the template class can be moved to the header file cola.h. This ensures that the implementation is available to all translation units that include the header file.

Reason for Header File Inclusion

Putting the implementation in the header file avoids the need for explicit instantiation. It guarantees that the template class and its member functions are available to every translation unit that includes the header file. This approach is commonly used for template classes that are widely used throughout the codebase.

Additional Notes:

• Ensure that only one implementation of the template class exists in the entire codebase.
• The implementation of the template class must be after all class definitions.
• If the template class is declared in multiple header files, the implementation should be put in a separate header file that is included in all other header files where the template class is used.

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