[gmx-developers] uninitialized data

Erik Marklund erikm at xray.bmc.uu.se
Wed Apr 22 10:41:46 CEST 2009

Erik Lindahl skrev:
> On Apr 21, 2009, at 9:00 PM, David van der Spoel wrote:
>> Alexander Herz wrote:
>>> of course it must be
>>> memset(fr,0,sizeof(t_forcerec)); as fr is a pointer
>> snew does this.
> In practice you're right, but:
> 1) It is incredibly bad coding habit to rely on the behaviour of 
> memory allocation for initializing objects.
> 2) Formally it is even wrong (but so is memset). There is nothing in 
> the ISO C standard that *requires* NULL to be represented by numerical 0.
> Cheers,
> Erik
I second that. There are for instance environment variables that makes 
the malloc-family of functions write non-zero bytes to (de)allocated 
memory. Although it's convenient to rely on eg. snew() I bet one can 
avoid some pretty hard-to-find mysterious bugs on certain systems by 
explicitly initializing objects whenever initialization is critical. The 
best time to do it is when implementing things in the first place; 
honsetly, how often does one go back to polish the code one wrote n 
months ago just to make it more compliant to eg. the C standard?

My 2 cents.

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Erik Marklund, PhD student
Laboratory of Molecular Biophysics,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,    75124 Uppsala, Sweden
phone:    +46 18 471 4537        fax: +46 18 511 755
erikm at xray.bmc.uu.se    http://xray.bmc.uu.se/molbiophys

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