How to use two constructors? - c++

Question

I have a code like this.
#include <iostream>
#include <vector>
using namespace std;
class AbstractValueC{
private:
long age = 0;
int abs;
bool spec = false;
public:
AbstractValueC() {
abs = 0;
}
AbstractValueC(int& a, bool b = false){
abs = *a;
spec = b;
}
AbstractValueC(int a, bool b = false){
abs = a;
spec = b;
}
int get_value() const {
return abs;
}
long get_age(){
return age;
}
};
int main(){
vector<AbstractValueC> v;
int init = 1;
int next = 2;
v.push_back(AbstractValueC(std::move(init)));
cout << "I have created first v element." << endl;
v.push_back(AbstractValueC(std::move(next)));
cout << "I have created second v element." << endl;
std::vector<AbstractValueC> result;
for (auto a : v) {
int pre = a.get_value();
result.push_back(AbstractValueC(pre));
}
cout << "I have created result." << endl;
return 0;
}
Please tell me how to solve the error of
invalid type argument of unary ‘*’ (have ‘int’)
abs = *a;
^
and the error
call of overloaded ‘AbstractValueC(int&)’ is ambiguous
result.push_back(AbstractValueC(pre));
^
I actually have a custom type (Abs) in place of int for the abs member in my actual code. Also the requirement is that I cannot call the default constructor of Abs in main. I can use abs = Abs::null;. So please suggest a solution that avoid calling the default constructor for Abs if I replace int with Abs in the class definition.

Answer 1

invalid type argument of unary ‘*’ (have ‘int’)
AbstractValueC(int& a, bool b = false){
abs = *a;
spec = b;
}
Argument a is an int reference, not a pointer, so you can't dereference as *a.
The code should be abs = a;
call of overloaded ‘AbstractValueC(int&)’ is ambiguous
As #strom points out in the comments, you have 2 similar constructors:
AbstractValueC(int& a, bool b = false)
AbstractValueC(int a, bool b = false)
Which the compiler cannot readily distinguish between. You should get rid of one of them.

Answer 2

The real problem is that you are using two constructors with the same signature :
How does the compiler choose between using :
AbstractValueC v=AbstractValueC(value);//int constructor
And
AbstractValueC v=AbstractValueC(value);//reference constructor
When you have
Int value = 0;//for example
To get rid of this error(ambigueous constructor call) you could either change one of the constructors or replace your reference constructor with a pointer constructor
To change the constructor to a pointer, you need to create a value pointer in your class and create a contructor:
// in class declaration
Int *pointerValue = nullptr;
AbstractValueC(int* pointer, bool b = false);
// implementation
AbstractValueC::AbstractValueC(Int *pointer, bool b=false) {
pointerValue=pointer;
}