Compilation of Multifile C++ Code with Template Functions

Question

Suppose, I'm writing a code that contains many template functions across many files. The code is supposed to be used with different datatypes. My first attempt was something like as follows (it's just an example, not my actual project):

main.cpp

#include <iostream>

#include "template.h"

int main() {
  using T = int;
  T val{ f<T>() };
  std::cout << val;
  return 0;
}

template.h

#ifndef TEMPLATE_H
#define TEMPLATE_H

template <typename T>
T f();

#endif  // TEMPLATE_H

template.cpp

#include "template.h"

template <typename T>
T f() {
  T val{ static_cast<T>(123) };
  return val;
}

Compiling the project gave the following error.

/usr/bin/ld: /tmp/ccEH5mLC.o: in function `main':
main.cpp:(.text+0x9): undefined reference to `int f()'
collect2: error: ld returned 1 exit status

Searching for the root of the problem here and there, I have found that it has something to do with template. ISO C++ provides 2 solutions:

1. Physically moving the definition of the template function into the .h file.
2. Adding the line template int f<int>(); (or template int f();) to the .cpp file.

The first solution may cause significant code bloat. Thus, as far as I understand, it's not widely used in real projects (I'm not a programmer, so, may be wrong).

The second one doesn't look flexible, since changing T type will require changing all template int f<int>(); (or template int f();) in all .cpp files. Or, if using multiple T types (int and double, for example) will require adding and/or modifying the exising lines.

So, the question is: What solutions (for compiling multiple files projects with many template functions) are used in real life?

Will be glad to hear about all solutions. (Maybe C++ macros can be somehow used? Or CMake features?)