using a class inside a class.

[phil.pellouchoud]

I did some searching online and i couldn't find anything in reference
to this.

I am using MinGW, gcc 4.3 and am having the following compilation
issue:

class CFoo
{
public:
...
private:
std::list<CFoom _children;
};

The complaint from the compiler looks like this:

c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In instantiation of
'__gnu_cxx::_SG IAssignableConc ept<CFoo>':
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: instantiated from 'std::list<CFoo ,
std::allocator< CFoo'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:216: error:
'__gnu_cxx::_SG IAssignableConc ept<_Tp>::__a' has incomplete type

So, basically, I think what it's saying is that it doesn't know how to
build the class because CFoo hasn't been defined by the time it's
trying to create it (i.e. incomplete type). I tried adding
"std::list<clas s CFoo>" as well, but that didn't work either. This
compiles on visual studio with some warnings.

I can make this work by making it "std::list<CFoo *>", but I'm
wondering if there's a way to get this to work as defined.

thanks for listening.

-phil

[Jim Langston]

ph************* *@gmail.com wrote:

I did some searching online and i couldn't find anything in reference
to this.

I am using MinGW, gcc 4.3 and am having the following compilation
issue:

class CFoo
{
public:
...
private:
std::list<CFoom _children;
};

The complaint from the compiler looks like this:

c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In instantiation of
'__gnu_cxx::_SG IAssignableConc ept<CFoo>':
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: instantiated from 'std::list<CFoo ,
std::allocator< CFoo'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:216: error:
'__gnu_cxx::_SG IAssignableConc ept<_Tp>::__a' has incomplete type

So, basically, I think what it's saying is that it doesn't know how to
build the class because CFoo hasn't been defined by the time it's
trying to create it (i.e. incomplete type). I tried adding
"std::list<clas s CFoo>" as well, but that didn't work either. This
compiles on visual studio with some warnings.

I can make this work by making it "std::list<CFoo *>", but I'm
wondering if there's a way to get this to work as defined.

thanks for listening.

All I can tell you is I've done this exact same thing in the past
successfully in both Microsoft Visual C++ .net 2003 and DevC++. Here is
something that compiles sucessfully in Microsoft Visual C++ .net 2003:

#include <list>

class CFoo
{
private:
std::list<CFoom _children;
};

int main()
{
CFoo Foo;
}

No warnings, no errors.

I don't know why your version of gcc is complaining, I don't think it
should, AFAIK this is perfectly legal, although I haven't read the standard
on it.

--
Jim Langston
ta*******@rocke tmail.com

[phil.pellouchoud]

Here's exactly what i get when I try to compile that code:

C:\>type foo.cpp
#include <list>

class CFoo
{
private:
std::list<CFoom _children;

};

int main()
{
CFoo Foo;

}
C:\>gcc -v
Using built-in specs.
Target: i386-pc-mingw32
Configured with: ../gcc-4.3.0/configure --prefix=/mingw --disable-nls
--enable-languages=c,c++ ,fortran,objc,o bj-c++,ada,
java --disable-win32-registry --disable-sjlj-exceptions --enable-
libstdcxx-debug --enable-version-specific-runtime-libs
--with-gmp=/mingw/src/gcc/gmp-mpfr-root --with-mpfr=/mingw/src/gcc/gmp-
mpfr-root --enable-libgcj --enable-concept-checks
--enable-shared
Thread model: win32
gcc version 4.3.0 (GCC)

C:\>gcc -o foo foo.cpp
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In instantiation of '__gnu_cxx::_S
GIAssignableCon cept<CFoo>':
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: instantiated from 'std::list<CFoo , std:
:allocator<CFoo '
foo.cpp:6: instantiated from here
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:216: error: '__gnu_cxx::_SG IAssigna
bleConcept<_Tp> ::__a' has incomplete type
foo.cpp:4: error: forward declaration of 'class CFoo'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In member function 'void __gnu_cxx
::_SGIAssignabl eConcept<_Tp>:: __constraints() [with _Tp = CFoo]':
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: instantiated from 'std::list<CFoo , std:
:allocator<CFoo '
foo.cpp:6: instantiated from here
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:208: error: using invalid field '__
gnu_cxx::_SGIAs signableConcept <_Tp>::__a'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:209: error: using invalid field '__
gnu_cxx::_SGIAs signableConcept <_Tp>::__a'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:209: error: using invalid field '__
gnu_cxx::_SGIAs signableConcept <_Tp>::__a'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: instantiated from 'std::list<CFoo , std:
:allocator<CFoo '
foo.cpp:6: instantiated from here
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:210: error: using invalid field '__
gnu_cxx::_SGIAs signableConcept <_Tp>::__a'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In member function 'void __gnu_cxx
::_SGIAssignabl eConcept<_Tp>:: __const_constra ints(const _Tp&) [with
_Tp = CFoo]':
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:210: instantiated from 'void __gn
u_cxx::_SGIAssi gnableConcept<_ Tp>::__constrai nts() [with _Tp = CFoo]'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: instantiated from 'std::list<CFoo , std:
:allocator<CFoo '
foo.cpp:6: instantiated from here
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:214: error: using invalid field '__
gnu_cxx::_SGIAs signableConcept <_Tp>::__a'

C:\>

[Ian Collins]

ph************* *@gmail.com wrote:

Here's exactly what i get when I try to compile that code:

C:\>type foo.cpp
#include <list>

class CFoo
{
private:
std::list<CFoom _children;

};

int main()
{
CFoo Foo;

}

C:\>gcc -o foo foo.cpp
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In instantiation of '__gnu_cxx::_S
GIAssignableCon cept<CFoo>':

<snip>

Looks like your compiler isn't configured correctly, try a gcc group.

--
Ian Collins.

[kwikius]

On Apr 28, 7:33*pm, "Jim Langston" <tazmas...@rock etmail.comwrote :

phil.pellouch.. [e-mail] wrote:

I did some searching online and i couldn't find anything in reference
to this.

I am using MinGW, gcc 4.3 and am having the following compilation
issue:

class CFoo
{
public:
* *...
private:
* *std::list<CFoo m_children;
};

The complaint from the compiler looks like this:

c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h: In instantiation of
'__gnu_cxx::_SG IAssignableConc ept<CFoo>':
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
stl_list.h:420: * instantiated from 'std::list<CFoo ,
std::allocator< CFoo'
c:\mingw\bin\../lib/gcc/i386-pc-mingw32/4.3.0/include/c++/bits/
boost_concept_c heck.h:216: error:
'__gnu_cxx::_SG IAssignableConc ept<_Tp>::__a' has incomplete type

So, basically, I think what it's saying is that it doesn't know how to
build the class because CFoo hasn't been defined by the time it's
trying to create it (i.e. incomplete type). *I tried adding
"std::list<clas s CFoo>" as well, but that didn't work either. *This
compiles on visual studio with some warnings.

I can make this work by making it "std::list<CFoo *>", but I'm
wondering if there's a way to get this to work as defined.

thanks for listening.

All I can tell you is I've done this exact same thing in the past
successfully in both Microsoft Visual C++ .net 2003 and DevC++. *Here is
something that compiles sucessfully in Microsoft Visual C++ .net 2003:

#include <list>

class CFoo
{
private:
* * std::list<CFoom _children;

};

int main()
{
* * CFoo Foo;

}

No warnings, no errors.

I don't know why your version of gcc is complaining, I don't think it
should, AFAIK this is perfectly legal, although I haven't read the standard
on it.

IMO gcc is correct. You could have a list of pointers or refs to CFoo
but not recursive types. One workaround *may* be to use a typedef
alias for CFoo. That may fool gcc, but I think its technically correct
to call this an error.

regards
Andy Little

[Ian Collins]

kwikius wrote:

On Apr 28, 7:33 pm, "Jim Langston" <tazmas...@rock etmail.comwrote :

>All I can tell you is I've done this exact same thing in the past
successfully in both Microsoft Visual C++ .net 2003 and DevC++. Here is
something that compiles sucessfully in Microsoft Visual C++ .net 2003:

#include <list>

class CFoo
{
private:
std::list<CFoom _children;

};

int main()
{
CFoo Foo;

}

No warnings, no errors.

I don't know why your version of gcc is complaining, I don't think it
should, AFAIK this is perfectly legal, although I haven't read the standard
on it.

IMO gcc is correct. You could have a list of pointers or refs to CFoo
but not recursive types. One workaround *may* be to use a typedef
alias for CFoo. That may fool gcc, but I think its technically correct
to call this an error.

Why? The class declares m_children to be a list of CFoo. It does not
attempt to use any members of std::list that require a complete type.

In effect, it's just like writing

#include <list>

class X;

class CFoo
{
private:
std::list<Xm_ch ildren;
};

class X {};

int main()
{
CFoo Foo;
}

The complete class definition is not required until std::list's default
constructor is instantiated in main().

--
Ian Collins.

[kwikius]

"Ian Collins" <ia******@hotma il.comwrote in message
news:67******** *****@mid.indiv idual.net...

kwikius wrote:

>On Apr 28, 7:33 pm, "Jim Langston" <tazmas...@rock etmail.comwrote :

>>All I can tell you is I've done this exact same thing in the past
successfull y in both Microsoft Visual C++ .net 2003 and DevC++. Here is
something that compiles sucessfully in Microsoft Visual C++ .net 2003:

#include <list>

class CFoo
{
private:
std::list<CFoom _children;

};

int main()
{
CFoo Foo;

}

No warnings, no errors.

I don't know why your version of gcc is complaining, I don't think it
should, AFAIK this is perfectly legal, although I haven't read the
standard
on it.

IMO gcc is correct. You could have a list of pointers or refs to CFoo
but not recursive types. One workaround *may* be to use a typedef
alias for CFoo. That may fool gcc, but I think its technically correct
to call this an error.

Why? The class declares m_children to be a list of CFoo. It does not
attempt to use any members of std::list that require a complete type.

Ah as to Why ... I Dunno. Hopefully someone of a more technical nature will
help out as to why. From the error messages gcc is using C++0x style Concept
checking.

Various things to try to diagnose the problem. Try some other dummy template
class than std::list.
If that succeeds then std::list is concept checking and wont allow itself to
be instantiated without a complete type or some such

There is presumably an option to turn it off . ..

regards
Andy Little

[Ian Collins]

kwikius wrote:

"Ian Collins" <ia******@hotma il.comwrote:

>>>

Why? The class declares m_children to be a list of CFoo. It does not
attempt to use any members of std::list that require a complete type.

Ah as to Why ... I Dunno. Hopefully someone of a more technical nature will
help out as to why. From the error messages gcc is using C++0x style Concept
checking.

It does, doesn't it? I thought that was a little odd, I didn't think
gcc had built in boost libraries.

--
Ian Collins.

[kwikius]

"Ian Collins" <ia******@hotma il.comwrote in message
news:67******** *****@mid.indiv idual.net...

kwikius wrote:

>"Ian Collins" <ia******@hotma il.comwrote:

>>>>
Why? The class declares m_children to be a list of CFoo. It does not
attempt to use any members of std::list that require a complete type.

Ah as to Why ... I Dunno. Hopefully someone of a more technical nature
will
help out as to why. From the error messages gcc is using C++0x style
Concept
checking.

It does, doesn't it? I thought that was a little odd, I didn't think
gcc had built in boost libraries.

Ahha yes its not C++0x Concepts, its old style concept checking . Theres
bound to be an option to turn that off.
Probbably a macro somewhere

Its all legit AFAIK.
After all std::list may want to for example instantiate some private
template type of allocate<sizeof (T)>
when its constructed for which it would obviously need the complete type.

regards
Andy Little

[kwikius]

"Jim Langston" <ta*******@rock etmail.comwrote in message
news:9S******** ********@newsfe 05.lga...

Ian Collins wrote:

>kwikius wrote:

>>"Ian Collins" <ia******@hotma il.comwrote:
>
Why? The class declares m_children to be a list of CFoo. It does
not attempt to use any members of std::list that require a complete
type.

Ah as to Why ... I Dunno. Hopefully someone of a more technical
nature will help out as to why. From the error messages gcc is using
C++0x style Concept checking.

It does, doesn't it? I thought that was a little odd, I didn't think
gcc had built in boost libraries.

That had thrown me off also, the boost error messages on something that
has nothing to do with boost. I wonder if it's some compiler switch?

FWIW following gives something similar. The trick is to make some
dependency, which must be going on in the O.P.

#include <list>

template<typena me T>
struct dummy : T{ };

struct CFoo {
dummy<CFoomy_li st;
};

int main()
{
CFoo foo;
}