Templates in Header Files

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Templates require compile-time generation of code: a templated function, for example, will be effectively turned into multiple distinct functions once a templated function is parameterized by use in source code.

This means that template function, member function, and class definitions cannot be delegated to a separate source code file, as any code that will use any templated construct requires knowledge of its definition to generally generate any derivative code.

Thus, templated code, if put in headers, must also contain its definition. An example of this is below:

// templated_function.h

template <typename T>
T* null_T_pointer() {
  T* type_point = NULL; // or, alternatively, nullptr instead of NULL
                        // for C++11 or later
  return type_point;

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