Multiple constructors for different arguments in C++

Question

I'm quite new to C++ and I was wondering if there is any way around duplicating constructors, with variations in the passed arguments. I need to identify the correct given value (either float or int), check if the float can nicely be casted to an integer (e.g. 1.0) and call another constructor that accepts two integers if my values pass the test.

If anyone as any tips on improving this solution in general that would be great.

Fraction(int n, int d) : numerator(n), denominator(d) {
    simplify(n, d);
}

Fraction(float n, float d) {
    if (!isInteger(n) && !isInteger(d)) {
        throw invalid_argument("Fractions only accept real numbers.");
    } else {
        Fraction(int(n), int(d));
    }
}

Fraction(int n, float d) {
    if (!isInteger(n) && !isInteger(d)) {
        throw invalid_argument("Fractions only accept real numbers.");
    } else {
        Fraction(int(n), int(d));
    }
}

Fraction(float n, int d) {
    if (!isInteger(n) && !isInteger(d)) {
        throw invalid_argument("Fractions only accept real numbers.");
    } else {
        Fraction(int(n), int(d));
    }
}

If you only want to support integer values, why do you want an option that takes float? — Oliver Charlesworth
– Oliver Charlesworth, Commented Oct 27, 2014 at 22:22
Your logic is wrong for the conditionals. Also, why are you checking that the arguments are integers? The compiler should do this already. Adding useless messages, and throwing exceptions just makes your code longer. — Ryan
– Ryan, Commented Oct 27, 2014 at 22:26
Because I want to be able to check if the passed parameter is a decimal. If I initialise my class with Fraction(9, 3.1), my values will be casted to int and thus become 9 and 3 but I want to be able to retrieve the original value of 3.1. — caubry
– caubry, Commented Oct 27, 2014 at 22:35
To clarify: you want to allow , at runtime, a float to be passed which does hold an exact integer value? — M.M
– M.M, Commented Oct 27, 2014 at 22:46

atlanteh · Accepted Answer · 2014-10-27 22:30:08Z

1

Well you could use only the floats ctor and test your parameters.
If you only have two ctors one for ints and one for floats, then only if both numbers are int the ints ctor will be called. otherwise the floats ctor will be called.

edited Oct 27, 2014 at 22:30

answered Oct 27, 2014 at 22:25

atlanteh

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2 Comments

caubry Over a year ago

Thanks! I guess I'm just going to stick with the first constructor, without doing any checks on the data type.

atlanteh Over a year ago

You can also use only the floats ctor and always check your parameters. Whatever suits you best :)

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