How can we initialize a parametrized constructor as default for a string?

Question

For an integer we can do it as

class A{
  int a;
public:
  A(int x = 0){ a = x; }
};

Answer 1

It is difficult to understand exactly what you are asking. I think you are asking how to specify a default value for a std::string parameter. If that is the case, you can do it like this:

class A{
  string a;
public:
  A(string x = ""){ a = x; }
};

or:

class A{
  string a;
public:
  A(const string &x = string()){ a = x; }
};

Though, in either case, you should be initializing the a member using the constructor's member initialization list instead of the constructor's body:

class A{
  string a;
public:
  A(string x = "") : a(x) { }
};

class A{
  string a;
public:
  A(const string &x = string()) : a(x) { }
};