error in constructor in class composition

Question

When I write a constructor of a class which has an other class' object, like in the example below, I get the compiling error error: no matching function for call to 'A::A()'

class A {
    int x;
public:
    A(int _x) {
        this->x=_x; } };

class B {
    A obj;
public:
    B(int x) {
        obj=A(x); } };

int main(){}

I know that by adding a constructor of A with no parameters (like A(){}) i would solve the problem, but there is another way to solve it without introducing a new constructor?

p.s.: i know using a pointer to A insted of a object of class A, would solve, but I want to know if there's a way keeping the object.

dont use pointers just to make the compiler happy. On the long run, you wont have lots of fun if you write code just to make the compiler shut up — 463035818_is_not_an_ai, Jan 23 '18 at 15:48

score 1 · Accepted Answer · answered Jan 23 '18 at 15:33

Use member initializer list.

For members that cannot be default-initialized, such as members of reference and const-qualified types, member initializers must be specified.

class B {
    A obj;
public:
    B(int x) : obj(x) {}
};

For your code, obj will be default initialized at first then assigned in the constructor's body. A can't be default initialized; which causes the error.

error in constructor in class composition

1 Answers1