Stray pointers

Stray pointers

[bruno]

Hi,

I was thinking about some problems involving programs written in c/c++ and
I don't realize why the compilers don't initialize every created pointer
to zero. Deleted pointers also are not automaticaly reassigned to zero
resulting in stray or dangling pointers (if the programmer do not take
care), and finally in possible crashes. Why this lack? Performance?
Thanks in advance,

Bruno A. Costa

Re: Stray pointers

[Eljay Love-Jensen]

Hi Bruno,

Correct.  Performance.

So always do this when declaring a pointer:

Foo* pFoo = NULL; // or else "= new Foo"

And do this when deleting a pointed to object:

delete pFoo;
pFoo = NULL;

...unless you've determined (via profiling) the performance penalty is too 
high for your application.

Or try to use std::auto_ptr to help with your pointer resource management. 
Except when the performance penalty is too high for your application.

Or considering using one of the more memory management friendly languages, 
such as Java.  (That's "friendly" in the sense of "safe and easy; one less 
thing to worry about".)

Sincerely,
--Eljay

Building gcc on Tru64

[laurence]

Dear all,
	I was wondering if anyone could help me in my attempts to build gcc
on Tru64 (Tru64 5.0, ev6). From looking at bug-reports, it seemed to me
that the gcc-3.3 branch does not build on Tru64; since my attempts
seemed to confirm this, I decided to try the gcc-3.4 branch. I can get
the compilers (c and c++) to build without failing using the following:

CC=/usr/bin/cc ../gcc/configure --prefix=/usr/local/gcc-3.4-20040322
--program-suffix=-3.4-20040322 --enable-languages=c,c++
--enable-version-specific-runtime-libs --disable-nls

However, when I try to compile some c++ programs, such as those included in
Lam MPI, I get runtime errors complaining that "_Ewcsftime" is undefined
in libstdc++. I have also built gcc using --disable-shared and then get
the errors while linking the programs.

I can find very little information about _Ewcsftime. I did find

http://gcc.gnu.org/ml/gcc-patches/2004-01/msg00495.html

and had a look at the wchar.h file from Compaq, which mentions
_Ewcsftime, and was wondering where else it might crop up. I was also
wondering if anyone could tell me if _Ewcsftime is supposed to be
defined in libstdc++ or if it is in some other library.

-- 
Laurence

Re: Building gcc on Tru64

[llewelly]

laurence@narya.org writes:

> Dear all,
> 	I was wondering if anyone could help me in my attempts to build gcc
> on Tru64 (Tru64 5.0, ev6). From looking at bug-reports, it seemed to me
> that the gcc-3.3 branch does not build on Tru64; since my attempts
> seemed to confirm this, I decided to try the gcc-3.4 branch. I can get
> the compilers (c and c++) to build without failing using the following:
> 
> CC=/usr/bin/cc ../gcc/configure --prefix=/usr/local/gcc-3.4-20040322
> --program-suffix=-3.4-20040322 --enable-languages=c,c++
> --enable-version-specific-runtime-libs --disable-nls
> 
> However, when I try to compile some c++ programs, such as those included in
> Lam MPI, I get runtime errors complaining that "_Ewcsftime" is undefined
> in libstdc++. I have also built gcc using --disable-shared and then get
> the errors while linking the programs.
> 
> I can find very little information about _Ewcsftime. I did find
> 
> http://gcc.gnu.org/ml/gcc-patches/2004-01/msg00495.html
> 
> and had a look at the wchar.h file from Compaq, which mentions
> _Ewcsftime, and was wondering where else it might crop up. I was also
> wondering if anyone could tell me if _Ewcsftime is supposed to be
> defined in libstdc++ or if it is in some other library.

Here is a shot in the dark. Use find, nm, and grep, like this:

find /usr/lib -name '*lib*so*' -print | xargs nm -A | & grep 'T.*_Ewcsftime.*' | less

Replace '/usr/lib' with the directories in which you expect to find libraries.
Replace '*lib*so*' with a pattern which you expect to match appropriate
    libraries.

-A is the gnu nm option to print the name of the file before each
    symbol. Look at the docs for your nm to  find an equivalent.

Re: Building gcc on Tru64

[laurence]

On Thu, 25 Mar 2004 llewelly@xmission.com wrote:
> laurence@narya.org writes:
> > 	I was wondering if anyone could help me in my attempts to build gcc
> > on Tru64 (Tru64 5.0, ev6). From looking at bug-reports, it seemed to me
> > that the gcc-3.3 branch does not build on Tru64; since my attempts
> > seemed to confirm this, I decided to try the gcc-3.4 branch.
<snip>
> > However, when I try to compile some c++ programs, such as those included in
> > Lam MPI, I get runtime errors complaining that "_Ewcsftime" is undefined
> > in libstdc++. I have also built gcc using --disable-shared and then get
> > the errors while linking the programs.
<snip>
> > and had a look at the wchar.h file from Compaq, which mentions
> > _Ewcsftime,
<snip>
> Here is a shot in the dark. Use find, nm, and grep, like this:
>
> find /usr/lib -name '*lib*so*' -print | xargs nm -A | & grep 'T.*_Ewcsftime.*' | less

Thanks - though it didn't seem to find anything for me, I'm afraid.
However I have now managed to get an apparently working compiler by
using the snapshot of 3.4 from 7th January. I'm quite satisfied with
this; however, I am a bit curious as to what might have happened in the
meantime (or what I've done to my system to cause this). One difference I
have noticed is that the snapshot from the 7th January did not create a
new wchar.h file (which I mentioned in my previous post). Perhaps I shall
try playing with the latest compiler source and see what I can find.

-- 
Laurence