Question

Heres the link to code and the error

I dont understand why the line return (const C&)cc; doesnt work.

Heres a paste of code and error

#include <stdio.h>

class C 
{
public:
    int i;
    explicit C(const C&)   // an explicit copy constructor
    {
        printf("\nin the copy constructor");
    }
    explicit C(int i )   // an explicit constructor
    {
        printf("\nin the constructor");
    }

    C()
    {
        i = 0;
    }
};

class C2
{
public:
    int i;
    explicit C2(int i )   // an explicit constructor
    {
    } 
};

C f(C c)
{   // C2558
//    c.i = 2;
//    return c;   // first call to copy constructor
C cc;
return (const C&)cc;
}

void f2(C2)
{
}

void g(int i)
{
//    f2(i);   // C2558
    // try the following line instead
     f2(C2(i));
}

int main()
{
    C c, d;
    d = f(c);   // c is copied
}

Output:

In function ‘C f(C)’: Line 36: error:
no matching function for call to
‘C::C(const C&)’ compilation
terminated due to -Wfatal-errors.

Answer 1

Examples of calling the explicit copy-constructor:

• http://ideone.com/bV4S7
• http://ideone.com/G0OYi

Of course, pass-by-value and return-by-value always call the copy constructor implicitly, so declaring the copy constructor explicit will prevent this (not necessarily a bad thing).