Re: Virtual Bytes is STL

anand chugh wrote:
:: On Aug 28, 4:12 pm, Ulrich Eckhardt <eckha...@satorlaser.com>
:: wrote:
::: anand chugh wrote:
:::: I am using Visual Studio 2005 and microsoft STL. Actually this is
:::: expected behaviour of STL , they have updated FAQ
:::: http://www.sgi.com/tech/stl/FAQ.html
:::
::: Wait: the STL and the C++ standard library are separate things.
::: By no means is what SGI writes in that FAQ mandatory for the
::: implementation of the C++ standardlibrary! The STL heavily
::: influenced the standard library, but they are separate things
::: today.
:::
:::: Why does Bounds CheckerTM say that I have memory leaks?
:::: This is not an STL bug. It is an artifact of certain kinds of
:::: leak detectors. [...]
:::
::: This accurately explains what is going on and is still valid
::: today.
:::
:::: This is a serious using default allocators, causing a program to
:::: keep that memory even if its not using that.
:::
::: huh? Serious bug? Serious performance enhancement?
:::
::: Uli
::
:: That is ok SGI and Microsoft STL are different, but both having
:: same behaviour.
:: Although SGI is having more allocators than default one but
:: microsoft support only default and we have to implement our own
:: to support this behaviour.
::
:: My main point is if in a program I have allocated vector of 5000
:: strings and after some time I have freed the vector then in no way
:: program should keep that memory for future uses.If that program is
:: a service then it will keep that memory forever until its not
:: stopped or computer is not shut down.That is not what I expected
:: from STL.
::
:: By default behaviour should be , as soon as vector is cleared its
:: memory should be free. If I want to allocate memory for that
:: vector I will call reserve again.
::
:: Does it not make sense?
::

No, it does not make sense. :-)

You are allocating virtual memory, not physical memory. If you have
unused memory from your cleared vector, AND another program needs more
space, your heap memory will be moved to the swap file, and the RAM
will be free again.

Releasing virtual memory makes no sense, as all programs will get its
own 2 GB anyway. If you run a lot of large programs, you might need a
large swap file, but that's a different story.

Running a single program and checking its memory use is not very
useful, as Windows will let the program use any amount of RAM, as long
as it is uncontended. Why bother to conserve, when you have plenty!

Bo Persson