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I have been given the assignment to make a "calculator" in c++, which takes any number data type as two inputs, calculates either the sum or product, and then logs the equation. All of this using template <typename T>. I have a hard time finding documentation to to my specific problems, which are:

  • How to setup functions and constructors with the defined return type.
  • How to search c++ error log efficiently, so I can fix errors just as easily as in 'C'.

My .hpp file:

#pragma once

#include <sstream>
#include "logger.hpp"

template <typename T>
class Calculator{
    public:
        Calculator(Logger *l);

        T sum(T a, T b);

        T multiply(T a, T b);

    private:
        Logger *logger;
};

My .cpp file:

#include "template_calculator.hpp"

Calculator::Calculator(Logger *l){
    logger = l;
}


Calculator::T sum(T a, T b){
    T c = a + b;
    std::string str_a = std::to_string(a);
    std::string str_b = std::to_string(b);
    std::string str_c = std::to_string(c);
    logger->log(str_a + " + " + str_b + " = " + str_c);
    return c;
}


Calculator::T multiply(T a, T b){
    T c = a * b;
    std::string str_a = std::to_string(a);
    std::string str_b = std::to_string(b);
    std::string str_c = std::to_string(c);
    logger->log(str_a + " * " + str_b + " = " + str_c);
    return c;
}

I have tried to follow the guidance of this guy: invalid use of template name without an argument list

.. but it doesn't solve my problems. I get the following errors - all of which I can't fin the solution to.

note: ‘template<class T> class Calculator’ declared here
7 | class Calculator{

error: invalid use of template-name ‘Calculator’ without an argument list
8 | Calculator::T sum(T a, T b){

Attempting to use the advice from above link:

    #include "template_calculator.hpp"

    template <typename T>
    Calculator<T>::Calculator(Logger *l){
        logger = l;
    }


    Calculator<T>::T sum(T a, T b){
        T c = a + b;
        std::string str_a = std::to_string(a);
        std::string str_b = std::to_string(b);
        std::string str_c = std::to_string(c);
        logger->log(str_a + " + " + str_b + " = " + str_c);
        return c;
    }


    Calculator<T>::T multiply(T a, T b){
        T c = a * b;
        std::string str_a = std::to_string(a);
        std::string str_b = std::to_string(b);
        std::string str_c = std::to_string(c);
        logger->log(str_a + " * " + str_b + " = " + str_c);
        return c;
    }

as per:

    template<typename T>
LinkedList<T>::LinkedList()
{
   start = nullptr;
   current = nullptr;
}

And similarly for other member functions.

Jens Dissing Poulsen
  • 29
  • 4
  • See this [related question](https://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file). – 1201ProgramAlarm Feb 19 '20 at 21:06
  • I have already seen and read this particular post, but doing as explained doesn't make the code compile. – Jens Dissing Poulsen Feb 19 '20 at 21:15
  • "*I have tried to follow the guidance of this guy: [...] but it doesn't solve my problems.*": It should solve your problem. Please show how you tried to apply the answer in that question to your code and then show the resulting error. Additionally consider that your function definitions in the `.cpp` are missing return types in their function head.... – walnut Feb 19 '20 at 21:27
  • Additionally consider that your function definitions in the .cpp are missing return types in their function head.... This I am aware of but putting anything results in it complaining 'T' not being defined. – Jens Dissing Poulsen Feb 19 '20 at 21:35
  • By "And similarly for other member functions. " Is it implied, that "template " is to be written for every function? – Jens Dissing Poulsen Feb 19 '20 at 21:41

0 Answers0