Re: References

Victor Bazarov <v.bazarov@comcast.invalid>
Thu, 11 Nov 2010 14:50:32 -0500
On 11/11/2010 2:14 PM, Andrea Crotti wrote:

Ian Collins<> writes:

Packer is initialises with the constant 10, not Packet.x.

A moment I don't get it now is
class Packer
     Packer(int& _x) : x(_x) {}
     int& x;
     void packData(char *);

class Packet
     int x;
     Packer p;
     Packet(int _x) : x(_x), p(_x) {}

int main() {
     Packet p1(10);
     cout<< p1.p.x<< endl;
     p1.x = 3;
     cout<< p1.p.x<< endl;
     return 0;

but should not here in the constructor
     Packet(int _x) : x(_x), p(_x) {}

call the constructor of Packer to set the value inside?

For a very short time (while the Packet constructor is running) the
reference inside the Packet::p member actually refers to a valid object
(the argument to the constructor of the Packet object). As soon as the
constructor returns, the temporary (the argument) is no more, and the
reference inside the 'p' member becomes invalid. Your program has
undefined behavior if it tries to refer to 'p1.p.x' after 'p1' has been

Do I need a "void setX(const int& _x)" in Packer then otherwise?

No, you need to understand what a reference is.

I do not respond to top-posted replies, please don't ask

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