Forward declaration and nested classes ..

[Susan Baker]

Hi,

I have the following code which refuses to compile:

Snippet from header file:

class C ;
class A ;
class L ;
class T ;


class TC {

private:
void *ct ;
std::vector < PB > dat ; /* One or more */
std::list < C > pat ;
std::list < A > nts ;
std::list < L > ls ;
std::list < T > tl ;
int bIdx ; /* base index */
myEnum sType ;
bool spread ;

protected:
class BPat {

public:
BPat() ;
~BPat() ;

virtual long gSD( void ) = 0 ;
virtual double gSV( void ) = 0 ;
//<snip> ...
};

public:

class TL : protected BPat {
private:
int sd ;
int ed ;
double sv ;
double ev ;
A text ; // <- Compiler complains here !!


Error message:
error C2079: 'TC::TL::text' uses undefined class 'A'


I used class A earlier on in the declaration of class TC, and that was
fine, why is the compiler suddenly (i.e. several lines further down),
complaining that A is an unidentified class?

Any pointers much apprreciated - mtia

S

 

[Victor Bazarov]

I have the following code which refuses to compile:

Snippet from header file:

class A ;

class TC {
std::list < A > nts ;
> protected:
> class BPat {};
public:
class TL : protected BPat {
A text ; // <- Compiler complains here !!

<rant>
See how I managed to shorten your code? Isn't it easier to read now?

Error message:
error C2079: 'TC::TL::text' uses undefined class 'A'


I used class A earlier on in the declaration of class TC, and that was
fine, why is the compiler suddenly (i.e. several lines further down),
complaining that A is an unidentified class?

The declaration of the 'nts' member doesn't need to know what the size
of 'A' is. The size of a list<A> does not depend on it. It will only
need to know the size of the list's stored object when you begin to add
to the list because then the compiler will try to use 'A's constructor.
OTOH when you declare 'TC::TL::text', the compiler needs to know the size
of 'A' to calculate the size of 'TC::TL'.

V