Re: what is this memory usage

From:

Markus Moll <markus.moll@esat.kuleuven.ac.be>

Newsgroups:

comp.lang.c++

Date:

Mon, 29 Oct 2007 15:57:18 +0100

Message-ID:

<4725f4d0$0$4374$9b4e6d93@newsspool4.arcor-online.net>

Hi

CMOS wrote:

consider the below code. it just creates a map and inserts 51000000
elements.

Um... no. It inserts at most 2^CHAR_BITS elements (Probably 256). Possibly
fewer if your char is signed.

when i check the memory usage , it shows an increase of
memory after the loop. the increase is around 2mb. i used "ps aux"
command and use the VSZ value.
why is this happening? i dont see any memory leaks as nothing is
created in heap/free store.
is this some kind of a memory fragmentation issue?

// memory ckeck 1 goes here
{
      std::map<std::string, int> mm;
      for(int i=0; i<51000000; ++i)
     {
std::string s;
s = i;

i is implicitly converted to a char here. The conversion is
implementation-defined if char is signed. Otherwise the value will be i
modulo 2^CHAR_BITS.

mm[s] = i;
}
}

// memory ckeck 2 goes here, and there is an increase in memory

See the comp.lang.c FAQ: http://c-faq.com/malloc/freetoOS.html

The same applies to C++.

Markus