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From: The|Godfather on 24 Oct 2006 18:14
Hi there
I have a problem with a program code. As the code is huge and is
copyrighted I just simulated the error with some useless code.
Here is the full report now:

gcc --version: gcc (GCC) 3.4.2
uname -rmo: 2.6.5-7.201-smp x86_64 GNU/Linux
compile command:
gcc -c -I/users/dstanche/problem test1.cpp
Error Message:
"test1.cpp: In constructor
`test1::StatementInternals::StatementInternals()':
test1.cpp:8: error: invalid use of nonstatic data member
'test1::stmt_internals' "

CODE :

example.h:
------------
class example {

public:
example() {;}
inline int giveIt(){return 2;}

};

--------
test1.h
-------
#include <example.h>

class test1 :example{
class StatementInternals;
public:

test1();
private:
StatementInternals * stmt_internals;

};

---------
test1I.h
---------
class test1::StatementInternals
{
public:
StatementInternals();
unsigned long *length;
bool select_statement;
int stmt_counter;

};

--------
test1.cpp
-------
#include <test1.h>
#include <test1I.h>

test1::StatementInternals::StatementInternals()
: length(0), select_statement(0)

{
stmt_counter=stmt_internals->giveIt(); // THE PROBLEM LINE IS THIS
ONE

}

test1::test1():stmt_internals(new StatementInternals){}

int main() {

return 0;
}

-------

As you can see the code does not do anything special. I have NO idea
why the problem occurs. Please advice.

Dragomir Stanchev


--
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From: Alberto Ganesh Barbati on 24 Oct 2006 22:46
The|Godfather ha scritto:
> class test1 :example{
> class StatementInternals;
> public:
>
> test1();
> private:
> StatementInternals * stmt_internals;
>
> };
>
> <snip>
>
> --------
> test1.cpp
> -------
> #include <test1.h>
> #include <test1I.h>
>
> test1::StatementInternals::StatementInternals()
> : length(0), select_statement(0)
>
> {
> stmt_counter=stmt_internals->giveIt(); // THE PROBLEM LINE IS THIS
> ONE

There are two different errors here. Your compiler is apparently
reporting only the first one however.

Forget for a moment that StatementInternals is a nested class of test1
and that stmt_internals is private. Would that work? No, because in
order to use a non-static member of a class you need to provide an
*instance* of such class. For example:

void foo(test1* ptr)
{
stmt_internal; // ERROR: which stmt_internal?
ptr->stmt_internal; // OK: THE stmt_internal of *ptr
}

Your case is the same: you don't have an instance of class test1 to work
on and you can't use stmt_internals without providing one.

Don't be fooled by the fact that class StatementInternals is nested in
class test1. They are still two different classes and there is *no*
implicit containment relationship between them.

The other mistake is that stmt_internal is a pointer to an object of
class test1::StatementInternals, but that class does *not* have a
giveIt() member function. giveIt() was defined in class example and so
it's inherited by class test1, but StatementInternals does *not* inherit
from test1 (nor from example).

Morale: nesting doesn't imply neither containment nor inheritance.

HTH,

Ganesh

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