C ++构造函数基于参数类型调用另一个构造函数

Question

I have this class

class XXX {
    public:
        XXX(struct yyy);
        XXX(std::string);
    private:
        struct xxx data;
};

The first constructor (who works with a structure) is easy to implement. The second I can parte one string in a specific format, parse and I can extract the same structure.

My question is, in java I can do something like this:

XXX::XXX(std::string str) {

   struct yyy data;
   // do stuff with string and extract data
   this(data);
}

Using this(params) to call another constructor. In this case I can something similar?

Thanks

Answer 1

The term you're looking for is " constructor delegation " (or more generally, " chained constructors "). Prior to C++11, these didn't exist in C++. But the syntax is just like invoking a base-class constructor:

class Foo {
public:
    Foo(int x) : Foo() {
        /* Specific construction goes here */
    }
    Foo(string x) : Foo() {
        /* Specific construction goes here */
    }
private:
    Foo() { /* Common construction goes here */ }
};

If you're not using C++11, the best you can do is define a private helper function to deal with the stuff common to all constructors (although this is annoying for stuff that you'd like to put in the initialization list). For example:

class Foo {
public:
    Foo(int x) {
        /* Specific construction goes here */
        ctor_helper();
    }
    Foo(string x) {
        /* Specific construction goes here */
        ctor_helper();
    }
private:
    void ctor_helper() { /* Common "construction" goes here */ }
};

Answer 2

Yes. In C++11, you can do that. It is called constructor delegation .

struct A
{
   A(int a) { /* code */ }

   A() : A(100)  //delegate to the other constructor
   {
   }
};