CODEWITHSUNDEEP
c++templatesconstructortype-conversionoperator-overloading
Huy Le
Huy Le

Reputation: 1738

Ambiguous overload for operator C++

#include <iostream>
using namespace std;

class StringNum {
public:
    string s;
    StringNum() {s = "";}
public:
    StringNum(int n) {
        for (int i=1; i<=n; i++) s += "x";

    }

    operator int () {
        return s.length();
    }

    StringNum operator - (StringNum v) {
        int len = s.length() - v.s.length();
        StringNum res;
        for (int i=1;i<=len;i++) res.s += "x";
        return res;
    }

    /* // long solution. But this will allow the program to run.
    template <class T>
    StringNum operator - (T value) {
        return (*this) - StringNum(value);
    }
    */
};

int main()
{
    StringNum x(4);
    cout << 3 - x; // this compiles
    cout << x - 3; // error: ambiguous overload for operator - 
                   // change the program so that the 2nd line output 2
    return 0;
}

So I have a class that can be upcast from int/downcast to int (this is the simplified version, in the actual version StringNum is HighPrecisionFloat, and int is int/float/double/.. . etc).

When I compile the program, the error message 

In function 'int main()':|
error: ambiguous overload for 'operator-' (operand types are 'StringNum' and 'int')|
note: candidate: operator-(int, int) <built-in>|
note: candidate: StringNum StringNum::operator-(StringNum)|

This happens because there are 2 ways to understand x - 3 :

a) int(x) - 3
b) x - StringNum(3)

One way to do this is to use template for each operator (+, -, *, /, dot product, etc...) But that is not very convenient because I have to write templates for each operator.

Is there a better solution to this problem? I wish to call x - StringNum(3). Thank you.

Upvotes: 0

Views: 234

Answers (1)

Kaldrr
Kaldrr

Reputation: 2850

You can make your constructor and conversion to int explicit.

The compiler won't make implicit conversion between those types anymore, but you can still use them like so.

auto stringNum = StringNum{3}; //int to StringNum
int y = static_cast<int>(stringNum);

Upvotes: 1

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