C++ - Template function that can return different types?

Question

I'm working on a section of code that allows the user to search by different types ( double / string / date (custom class)). This involves a method called readInSearchCriteria() that I have tried to set as a template. I have done some research into template functions and here is what I have so far:

//template function to process different datatypes
template <typename T> UserInterface::readInSearchCriteria() const {
    //template instance to hold data input from keyboard
    T t;
    //prompt user to enter a value
    cout << "\n ENTER SEARCH CRITERIA: ";
    //read-in value assigned to template variable
    cin >> t;

    //return initialised template variable
    return t;
}

I have called this at one point in the program to process a double like so:

double amount = theUI_.readInSearchCriteria<double>(); //works absolutely fine

However, when I tried to call it on a string , I was given the following error by the compiler:

no suitable constructor exists to convert from "int" to "std::basic_string, std::allocator>"

Would anyone be able to offer me any advice on what might be going wrong here?

Answer 1

You have a typo in your function declaration: you're not specifying a return type, so the compiler is defaulting to int .

You need to add T as the return type:

template <typename T>
T UserInterface::readInSearchCriteria() const {
    ...
    return T
}

Answer 2

The method readInSearchCriteria doesn't have a return type. You have to specify the return type for a function, here it is implicit int because you haven't specified one.

template <typename T> T UserInterface::readInSearchCriteria() const;