[Bug c++/17194] New: Some combined features of the C++ lenguage plus a mistake make g++ do a segmentation fault.

[Bug c++/17194] New: Some combined features of the C++ lenguage plus a mistake make g++ do a segmentation fault.

[staube at t2 dot technion dot ac dot il]

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Bug-report on templates, static const members and hided non const 
initialization  or in other words, "Writing a really strange code to make g++ 
crash HOW-TO"
*******************************************************************************
*******

My code makes the following versions of g++ crash with Segmentation Fault, no 
other 

messages than the segmentation fault itself and how to report a bug occur.
1) g++ (GCC) 3.3.2 20031022 (Red Hat Linux 3.3.2-1) on Feodora Core 1 running 
inside 

Cooperative Linux(linux kernel running on top of windows), compiler installed 
using apt-get 

getting everything from freshrpms.com
2) g++ (GCC) 3.3.3 (cygwin special), downloaded from cygwin site using the 
standard 

installer running in WinXP Professional SP1.
3) g++ (GCC) 3.2.3 (mingw special 20030504-1), downloaded in binary installer 
from myngw 

site, it´s running in WinXP Professional SP1.
4) g++ version 3.0.4 running on SunOS 5.8

The system where all versions out of SunOs are running:
Toshiba Satellite laptock with an intel Pentium 2.20 Ghz 240 RAM (the other 16 
are for the 

video card???). Does it matter anyway?

The comand line its a little dissapointig for a Segmentation Fault:
$ g++ main2.cpp


The contents of the file main2.cpp are no less dissapointing:
   (it doesnt do any include, so i post the cpp file itself instead of the ii 
file
     which looks exactly the same).
 ------------------------------------------------------------------------------
---
/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCOD
E/
-------------------------------------------------------------------------------
-
int function1()
{
    return 1;
}

template <class aType>
class Class1
{
 public:
     static const int var1 =  function1();
};

  /* Notice that the following line should not be used for static const 
variables
   *   i agree with that, however it should not make gcc crash but rather show 
an error
   *   message. At least thats my opinion ;-)
   */
const int Class1<int>::var1;

int main(int argc, char *argv[])
{
  int var2 = Class1<int>::var1;
  return 0;
}
 ------------------------------------------------------------------------------
--
/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCOD
E/
-------------------------------------------------------------------------------
-

What do i think about the error? (and other error which i think is related):
Listening to my opinion is very important, because i am important, i am the 
center of my 

universe :-)
This is the smallest programm that causes this same error (Segmentation Fault 
in g++).
Trying to reduce it:
1) If I delete the const keyword from the declaration and move function2() to 
the 

definition of the variable i get a successfull compilation.vthe program
2) If i delete the line which says "const int Class1<int>::var1;" i get a 
linker error but 

no segmentation fault.
3) If i deñete the function2() call and add the number 1 directly and erase 
the line which 

says "const int Class1<int>::var1;" i get another successfull compilation.
4)  **IMPORTANT** if i make class1 a non template class ( i delete "template 
<class aType>" 

and the other template stuff) i get compilation mistakes!!!! this means that 
building a 

class as a template make the compiler ignore some errors which is making g++ 
confused.
5) If i do not instanciate the template i get another succesfull compilation.


How to get to the error?
First look at a full-working first version of the programm:
 ------------------------------------------------------------------------------
---
/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCOD
E/
-------------------------------------------------------------------------------
-
class Class1
{
 public:
     static const int var1 =  1;
};


int main(int argc, char *argv[])
{
  int var2 = Class1::var1;
  return 0;
}
 ------------------------------------------------------------------------------
--
/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCOD
E/
-------------------------------------------------------------------------------
-

This works nice, now, we would like to use func2 to initialize var1... this is 
the code:
 ------------------------------------------------------------------------------
---
/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCOD
E/
-------------------------------------------------------------------------------
-
int function1()
{
  return 1;
}

class Class1
{
 public:
     static const int var1 =  function1();
};


int main(int argc, char *argv[])
{
  int var2 = Class1::var1;
  return 0;
}
 ------------------------------------------------------------------------------
--
/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCOD
E/
-------------------------------------------------------------------------------
-
This time time compilation fails with the following error:
main2.cpp:9: error: field initializer is not constant

You might be right, this is not a correct programm, anyway, the compiler still 
has no 

errors.

Now, imagine i still haven't compile this file so i don't know there is an 
error in my code 

, i would like  to make everything more general so i will make Class1 a 
tempate class.
New code: 
 ------------------------------------------------------------------------------
---
/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCODE/STARTCOD
E/
-------------------------------------------------------------------------------
-
int function1()
{
  return 1;
}


template <class aType>
class Class1
{
 public:
     static const int var1 =  function1();
};


int main(int argc, char *argv[])
{
  int var2 = Class1<int>::var1;
  return 0;
}
 ------------------------------------------------------------------------------
--
/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCODE/ENDCOD
E/
-------------------------------------------------------------------------------
-
now gcc bypasess completly the mistake in var1 initialization... it compiles 
the file (I 

have no idea what it writes in assembler) and it only reports a mistake in 
linking time.
/full/Path/Hided/For/Reporting/the/Bug/ccnctzKQ.o(.text+0x29):main2.cpp: 
undefined 

reference to `Class1<int>::var1'
This is already the mistake..... a static const should have no memory so there 
should be no 

reference to it, but somehow the combination of template and non static 
incorrect 

initilization confuses gcc.
Since this is a normal ld mistake i only have to define Class1<int>::var1 to 
bypass it so i 

add the line: "const int Class1<int>::var1;" and then get the nasty 
Segmentation Fault in 

every plataform that i tried it on.

So this is the end of my bug report, i worked a lot to make it very complete 
and to make this minimal programm to reproduce the bug. I hope you like the 
report ;-) I guess you wont.

Anyway, can you answer me a little additional question: why var1 cannot be 
initialized by a function, should i use some other mechanism which replaces 
it? how can i calculate a value for var1 at compile time???

Thank you very much in advance for fixing this, answering my question and 
continuing to do this great compiler collection which is such an important 
part of GNU/Linux, hey you see, i haver been reading all this stuff about the 
role of GNU.
Sincerilly,
Marcelo Taube

-- 
           Summary: Some combined features of the C++ lenguage plus a
                    mistake make g++ do a segmentation fault.
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: staube at t2 dot technion dot ac dot il
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: several
  GCC host triplet: several
GCC target triplet: several


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17194

[Bug c++/17194] Some combined features of the C++ lenguage plus a mistake make g++ do a segmentation fault.

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-08-25 23:38 -------
Fixed in 3.4.0 most likely by the parser.
Note the code is invalid (without the template):
gcc pr17194.cc
pr17194.cc:10: error: `int function1()' cannot appear in a constant-expression
pr17194.cc:10: error: a function call cannot appear in a constant-expression

With the template part:
pr17194.cc:10: error: `int function1()' cannot appear in a constant-expression
pr17194.cc:10: error: a function call cannot appear in a constant-expression
pr17194.cc:19: error: too few template-parameter-lists

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
           Keywords|                            |ice-on-invalid-code
         Resolution|                            |FIXED
   Target Milestone|---                         |3.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17194

[Bug c++/17194] Some combined features of the C++ lenguage plus a mistake make g++ do a segmentation fault.

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-08-25 23:42 -------
It wasn't a regression, so need to fix on any release branch. 
 
As for the bug report: thanks a lot, we very much appreciate small 
testcases with explanation! 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17194