I'm not coding much in C++, so please forgive me if this is trivial.
My class "Foo" looks somewhat like this:
class Foo {
public: Foo(int n) { }
};
Another class "Bar" is now supposed to have a class member of type "Foo".
class Bar {
private: Foo f;
};
This obviously fails, because there is no constructor for "Foo" that does not require any arguments. However, stuff like Foo f(1); fails, too.
Is there any way to solve this problem? Or am I supposed to use a pointer here?
class Bar {
public:
Bar():f(0) { }
explicit Bar(int n):f(n) { }
private: Foo f;
};
write your own c-tors, using initializer-list, or write c-tor without parameters in Foo, or use pointer, or in C++11 you can write
class Bar {
public:
private: Foo f = Foo(1);
};
This can be handled in 2 different way.
(1) Provide appropriate argument constructor for class Foo
You can either introduce a no argument constructor Foo() or edit the current one accepting default argument, i.e. Foo(int n = 0)
(2) Call constructor of class Foo inside the Bar with appropriate arugment
e.g.
class Bar {
...
Bar() : f(0) {} // (a) pass the argument explicitly
Bar(int n) : f(n) {} // (b) receive argument inside Bar()
};
explicit to forbid for unintended conversions, like in your example from int to Bar. I would use explicit Bar(int n=0) : Foo(n) {} in this case.
Bar() : Foo(0) and Bar() : f(0)?
Foo is not a base class, so you cannot call it's constructor that way. You have to say which member you want to initialize.Foo(0) calls c-tor of base class Foo, so it is wrong here. f(0) calls c-tor of f class member.You may have a default constructor for Foo or use pointer of Foo in class Bar and set an object later.
Bar constructor that soverly constructs a Foo, which should be most preferred.I guess if your Foo needs an argument to construct there are two possibilities:
- Either your Bar will use a static number for constructing his own Foo (all Bar will have the same n in Foo)
- Either your Bar's will have different numbers in their member Foo. You can then pass a number to Bar constructor as follows:
class Bar {
Bar(int n) : Foo(n) { ... } ;
}
