g++ copy-constuctor

[sotlef]

I want to undestand following problem... I have a code:
struct INT
{ };

struct LP
{
LP(const INT &p);
LP& operator=(const INT &p);
};

struct P
{
operator INT () const;
};

int main()
{
P pi1;
LP lpi2(pi1); // OK
LP lpi2_ = pi1; // FAILS!
lpi2 = pi1; // OK
}
in '//FAILS!' string i have compilation error in g++ (4.1.3). but i don't undestand why? can somebody help me how to fix stuctures to successfully compilation this (line) line without changes it (it - line with // FAILS comment)?

[sotlef]

maybe all sleep yet.. okey, i'm go sleep too, check answers tomorrow

[gerard4143]

LP lpi2_ = pi1; // FAILS!

lpi2 = pi1; // OK

The first one is a constructor of sorts and the second one is the equals operator which you just happen to have defined...G4143

struct INT
{

};

struct LP
{
	LP(const INT &p);
	LP& operator=(const INT &p);
};

struct P
{
	operator INT () const;
};

int main()
{
	P pi1;
	LP lpi2(pi1); // OK
	//LP lpi2_ = pi1; // FAILS!
	lpi2 = pi1; // OK
}

Actually the lines you have marked OK are not. When you rem out the troubling line you get a whole bunch of new compiler errors...

Why are you using structures for what is clearly classes?...Gerard4143

[Rubberman]

This is not allowed by the current C++ standards. To use an implicit copy constructor, such as you are doing ,where the value on the RHS of the assignment is a type which has to be used to construct a temporary of the class you are trying to copy, is not allowed. IE:

LP lpi2(pi1);

is allowed, as you are not using the assignment operator.
as is this:

LP lpi2_ = LP(pi1);

as you are constructing an LP object explicitly, But,

LP lpi2_ = pi1;

is not allowed. The gnu compilers are very standards-aware these days, and this will, as you have seen, generate an error.