Is constructor's parameter allowed to have a default value? Looks likes No.

Question

I tested it with some codes but I'm still not sure.

Answer 1

Yes, it is allowed. But it causes ambiguity in cases where you declare a default constructor as well.

Eg - C++ Code:

class A
{
int var;
public :
A() {var = 0;}
A(int v = 0) {var=v;}
};
int main()
{
A obj;
// Error
}

The error occurs because the compiler is unable to determine which constructor you want to call. Is it constructor 1, with no arguments, or constructor 2 with the default 0? Thus there exists an ambiguity.

Only in such cases you can't use default parameters, but for others you can.