No subject
Tue Jan 15 14:41:49 EST 2013
DESCRIPTION
The alloca() macro allocates size bytes of space in the stack frame of=
the caller. This temporary space is automatically freed on return.
I am planning on using it for some dimension sized array in compiled templa=
teless code, in lieu of C99 dynamic stack based arrays.
Best as I can tell Windows defines it as _alloca, so a little CMake try com=
pile is going to be needed, not a big deal.
Thanks,
Brad
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<div>
<div><font class=3D"Apple-style-span" face=3D"Consolas,monospace">I can't t=
hink of a single reason in ITK to use alloca. Pretty much every use case fo=
r alloca can be implemented using C++ language features in a more r=
obust manner.</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace"><br>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace">Maybe it'=
s unfair to say, but I think that the only reason it hasn't fallen out of u=
se entirely is the esteem in which it
is held by certain programmers associated with the GNU project. That's the=
one place it crept into VTK -- a bison-generated parser they've been modif=
ying for years.</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace"><br>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace">The follo=
wing has been a workaround I've used since C++ hasn't supported dyn=
amically sized arrays in the past -- I believe
it is a gnu extension (that, by the way, uses alloca under the covers). Of=
course, in most cases, it is preferable to use a STL container. I do=
n't remember who said it first but it's true: Arrays are to data what goto =
is to code.</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace"><br>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace">It is ver=
y nearly as efficient as raw array access, and the actual array is on the h=
eap:</font></div>
<div><font class=3D"Apple-style-span" face=3D"Consolas,monospace">
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><br>
</div>
<div>
<div>#include <cstddef></div>
<div><br>
</div>
<div>template <typename TElement></div>
<div>class DynArray</div>
<div>{</div>
<div>public:</div>
<div> typedef std::size_t size_type;</div>
<div> DynArray(size_type numElements) : m_Size(numElements)</div>
<div> {</div>
<div> this->m_Array =3D new TElement[numElements];</=
div>
<div> }</div>
<div> ~DynArray()</div>
<div> {</div>
<div> delete [] this->m_Array;</div>
<div> }</div>
<div> TElement &operator[](size_type idx)</div>
<div> {</div>
<div> if(idx > this->m_Size)</div>
<div> {</div>
<div> throw;</div>
<div> }</div>
<div> return this->m_Array[idx];</div>
<div> }</div>
<div> const TElement &operator[](size_type idx) const</div>
<div> {</div>
<div> if(idx > this->m_Size)</div>
<div> {</div>
<div> throw;</div>
<div> }</div>
<div> return this->m_Array[idx];</div>
<div> }</div>
<div>private:</div>
<div> TElement *m_Array;</div>
<div> size_type m_Size;</div>
<div>};</div>
</div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><br>
</div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><br>
</div>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace">-- <=
/font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace">Kent Will=
iams norman-k-williams at uiowa.edu</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace"><br>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace"><br>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Calibri,sans-serif; font-size:1=
4px"><font class=3D"Apple-style-span" face=3D"Consolas,monospace"><br>
</font></div>
<div style=3D"color:rgb(0,0,0); font-family:Consolas,monospace; font-size:1=
2px"><br>
</div>
</div>
<div style=3D"color:rgb(0,0,0); font-family:Consolas,monospace; font-size:1=
2px"><br>
</div>
<div style=3D"color:rgb(0,0,0); font-family:Consolas,monospace; font-size:1=
2px">On 3/12/13 7:54 AM, "Bradley Lowekamp" <<a href=3D"mailto=
:blowekamp at mail.nih.gov">blowekamp at mail.nih.gov</a>> wrote:</div>
<div style=3D"color:rgb(0,0,0); font-family:Consolas,monospace; font-size:1=
2px"><br>
</div>
<blockquote id=3D"MAC_OUTLOOK_ATTRIBUTION_BLOCKQUOTE" style=3D"color:rgb(0,=
0,0); font-family:Consolas,monospace; font-size:12px; border-left-color:rgb=
(181,196,223); border-left-width:5px; border-left-style:solid; padding-top:=
0px; padding-right:0px; padding-bottom:0px; padding-left:5px; margin-top:0p=
x; margin-right:0px; margin-bottom:0px; margin-left:5px">
<div>Hello,</div>
<div><br>
</div>
<div>I am thinking about using the "alloca" function in some code=
I'm working on for ITK, and wonder what other people think of it or others=
experience...</div>
<div><br>
</div>
<div>From the BSD Library Functions Manual:</div>
<div><br>
</div>
<div>DESCRIPTION</div>
<div> The alloca() macro allocates size bytes of sp=
ace in the stack frame of the caller. This temporary space is au=
tomatically freed on return.</div>
<div><br>
</div>
<div>I am planning on using it for some dimension sized array in compiled t=
emplateless code, in lieu of C99 dynamic stack based arrays.</div>
<div><br>
</div>
<div>Best as I can tell Windows defines it as _alloca, so a little CMake tr=
y compile is going to be needed, not a big deal.</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Brad </div>
<div>_______________________________________________</div>
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ww.kitware.com/opensource/opensource.html</a></div>
<div><br>
</div>
<div>Kitware offers ITK Training Courses, for more information visit:</div>
<div><a href=3D"http://kitware.com/products/protraining.php">http://kitware=
.com/products/protraining.php</a></div>
<div><br>
</div>
<div>Please keep messages on-topic and check the ITK FAQ at:</div>
<div><a href=3D"http://www.itk.org/Wiki/ITK_FAQ">http://www.itk.org/Wiki/IT=
K_FAQ</a></div>
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</blockquote>
<br>
<br>
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Notice: This UI Health Care e-mail (including attachments) is covered by th=
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