Template class with only static methods Implementation using .cpp file giving error

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I'm trying to implement a class in C++ which contains most of the functions which I might need to use across different class hierarchies (the project has multiple different inheritance trees).

After reading through and taking advise from multiple answers for this kind of implementation on Stack overflow, Why can templates only be implemented in the header file? I decided to implement this using a .h file and 2 different .cpp files. I tried to implement a small test case using this FAQ as a guideline. The code is as below:

test.h

#ifndef TEST_H
#define TEST_H

#include <iostream>
#include <cmath>
#include <complex>

template<typename T> 
class test{
public:
static bool IsClose(const T &a, const T &b);
};
#endif

testImpl.h

#include "test.h"

template <typename T> 
bool test<T>::IsClose(const T &a, const T &b){
    return (std::abs(a-b) <= (1e-8 + 1e-5 * std::abs(b)));
}

testImpl.cpp

#include "testImpl.h"

template class test<int>;
template class test<double>;

main.cpp

#include "test.h"
#include <iomanip>
int main(){
    std::cout << std::boolalpha << test<double>::IsClose(1e-7,1.1e-7) << std::endl;
    return 0;
}

On compiling using g++ -o test main.cpp testImpl.cpp I'm getting the following error:

main.cpp: In function ‘int main()’:
main.cpp:4:36: error: ‘test’ is not a template
     std::cout << std::boolalpha << test<double>::IsClose(1e-7,1.1e-7) << std::endl;

If anyone can advise me on where I'm going wrong your help will be much appreciated. Thanks in advance!! Also if there is a better method to achieve what I'm trying to do, your thoughts are welcome on that matter as well.

ubuntu-18.04 c++17 c++11 c++
1 Answers

I figured it out finally. I needed to let the compiler know that it needs to use a more recent version of C++. So, g++ -std=c++17 -o test main.cpp testImpl.cpp compiled the code for me perfectly fine.

The need for using -std flag arises only when you're using the gcc version 7.5.0. All versions of gcc after it, work with the g++ -o test main.cpp testImpl.cpp.

user_109353160
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