Question

I’m confused about following program about why it calls first constructor.

class A  
{  
public:  
        A(const char *c="\0")  
        {  
                cout<<"Constructor without arg";  
        }  
        A(string c)  
        {  
                cout<<"New one";  
        }  

};  

int main()  
{  
        A a="AMD";  
        return 0;  
}  

Output is
Constructor without arg

Answer 1

"AMD" is a const char[], which is implicitly converted to const char*, so the first constructor [A(const char *c="\0")]is the best match.

Note that A(const char *c="\0") is not a constructor without an argument, it’s a constructor which takes a single const char* as an argument, and has an optional default value to use when a const char* isn’t specified. In this case, you’re passing a const char*, so it uses it.