c++/6001: g++ problems with nested headers from > egcs-2.91.66 until 3.0.0

[mdeil@pallas.de]

>Number:         6001
>Category:       c++
>Synopsis:       g++ problems with nested headers from > egcs-2.91.66 until 3.0.0
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Mar 19 07:16:02 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Mario Deilmann
>Release:        gcc version 3.0 and other ...
>Organization:
>Environment:
SunOS pooh 5.7 Generic_106541-19 sun4u sparc SUNW,Ultra-4
>Description:
Hi,

I found some strange behaviour with some of the g++ versions greater than 2.91 on different platforms with a small C++ code (included)
I investigated a little more and found out that in my opinion the program was badly coded. The header files included each others and also some of the system headers. So I cleaned up all headers so that there are no more
includes in the header files. Collected the used system and program header's and added the std namespace. Wow, what a suprise now all gcc versions include 3.0 accepts the code. 

Can you give me some insight's what makes this program so PRBLEMATIC are this ANSI/ISO feature problems ? All compilers that produce errors find them in their own include files which confuses me. I thought that the problems should be located in the original source code. 
 
GCC 3.0 on Solaris for example:
 
poohtmp/mak> g++ -Wall -c buffer.cpp
In file included from
/home/mdeil/bin/../include/g++-v3/bits/basic_file.h:250,
                 from
/home/mdeil/bin/../include/g++-v3/bits/std_fstream.h:41,
                 from
/home/mdeil/bin/../include/g++-v3/backward/fstream.h:32,
                 from buffer.h:4,
                 from buffer.cpp:25:
 /home/mdeil/bin/../include/g++-v3/sparc-sun-solaris2.7/bits/basic_file_model.h:
In constructor 
`std::__basic_file<_CharT>::__basic_file(std::__c_lock*)':
/home/mdeil/bin/../include/g++-v3/sparc-sun-solaris2.7/bits/basic_file_model.h:39:
parse error before `;' token .............
^^^^^^^^^^^^^^^^^^^^^^^^^^^

Here my modification to get the code compile:

buffer.cpp NOW includes:

#include <stdio.h>
#include <string.h>
#include <time.h>
#include <stdio.h>
#include <string.h>
#include <fstream.h>

#include <iostream>

#include "common.h"
#include "misc.h"
#include "error.h"
#include "buffer.h"

using namespace std ;

What was the problem ? Why are the original include lines wrong ???

buffer.cpp ORIGINAL includes:

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <time.h>

#include "common.h" 
 ---> #include misc.h (no more includes)
#include "buffer.h"
 ---> #include <fstream.h>
 ---> #include <stdio.h>
 ---> #include <string.h>
 ---> #include "misc.h" (no more includes)
 ---> #include "error.h" (no more includes)

Although I seem to have solved the problem I don't understand it ???????
>How-To-Repeat:
simply type
g++ -Wall -ansi buffer.cpp or buffer.cc
>Fix:
Don't use nested header files - but I don't know why :).
>Release-Note:
>Audit-Trail:
>Unformatted:
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