CODEWITHSUNDEEP
c++classconstructor
Jaeho Choi
Jaeho Choi

Reputation: 65

Constructing an object other than specified parameters NOT giving me errors

I was going through a book called Programming Principles and Practices using C++ but found a strange behavior of class construction. Suppose I have a class as follows:

class Foo {
public:
    Foo(int x)
        : y { x } { }

private:
    int y;
};

and I have another class which has an instance of class Foo as its member object

class Bar {
public:
    Bar(Foo x)
        : y { x } { }

private:
    Foo y;
};

When I do the following:

int main()
{
    Bar obj_1 { Foo { 1 } };
    Bar obj_2 { 2021 }; // this doesn't give me error?

    return 0;
}

obj_1 was constructed as specified in the constructor, but obj_2 doesn't give me any error message and to me it seems it just magically works. My intention of having a member of a class as an instance of another class was to force the constructor to take a class instance as its argument, but not an integer.

Why doesn't it give me incorrect type error?

Upvotes: 1

Views: 45

Answers (1)

Cory Kramer
Cory Kramer

Reputation: 117876

You can prevent this implicit conversion by declaring the Foo constructor explicit

explicit Foo(int x) : y { x } { }

in main this would require the caller to change their obj_2 instantiation to

Bar obj_2 { Foo{2021} };

Upvotes: 1

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