Can you initialise in the class and in the constructor and is that correct?

Question

Considering the code below:

#include <iostream>

class tester
{
public:
    tester(){}
    explicit tester(double val) : 
        m_a(val) // I assume this now overwrites the "default" initialise value?
    {}
    double m_a {1.123}; // Default constructor value?
};


int main()
{
    tester t1;
    tester t2(2.456);

    std::cout << "t1:" << t1.m_a << std::endl;
    std::cout << "t2:" << t2.m_a << std::endl;

    return 0;
}

My question is, can you have both the initialise value in the class and in the constructor body? - how does the compiler resolve this? It appears that the constructor wins since the output of this program is:

t1:1.123
t2:2.456

The code you show is fine, and "I assume this now overwrites the "default" initialise value?" is correct. — Some programmer dude, Jun 08 '20 at 09:48
thank you - I linked the post to the suggested question that also has the answer I was looking for : ) — code_fodder, Jun 08 '20 at 10:21

score 3 · Accepted Answer · edited Jun 20 '20 at 09:12

Yes, for default member initializer,

Through a default member initializer, which is a brace or equals initializer included in the member declaration and is used if the member is omitted from the member initializer list of a constructor.

If a member has a default member initializer and also appears in the member initialization list in a constructor, the default member initializer is ignored for that constructor.

In the default constructor m_a is not mentioned in member initializer list, then it will be initialized by the default member initializer as 1.123. In tester::tester(double) m_a will be initialized by the member initializer list as the argument val.

Can you initialise in the class and in the constructor and is that correct?

1 Answers1