C / C++ / MFC Discussion Boards

George_George10-Nov-07 0:08

10-Nov-07 0:08

Hello everyone,

Two concepts about heap on Windows after reading MSDN document about heap functions.

1. Default heap. Each process has a default heap. But the default heap of different processes are different, right? Example, process 1 has default heap A and process 2 has default heap B, then A and B should be different heaps, right?

2. Why a process needs to allocate private heap, any practical use?

3. Are there any default global heap which different processes could share?

thanks in advance,
George

Re: heap

cmk10-Nov-07 12:20

cmk

10-Nov-07 12:20

1. A and B should be different heaps - Yes.
2. Practical uses - Yes.
3. Global heap - No.

...cmk

The idea that I can be presented with a problem, set out to logically solve it with the tools at hand, and wind up with a program that could not be legally used because someone else followed the same logical steps some years ago and filed for a patent on it is horrifying.
- John Carmack

Re: heap

George_George10-Nov-07 23:38

George_George

10-Nov-07 23:38

Thanks cmk,

Could you help to show some practical usage of creating private heap please?

regards,
George

Re: heap

Luc Pattyn10-Nov-07 15:31

Luc Pattyn

10-Nov-07 15:31

2. A process needs a heap to allocate dynamic things (e.g. malloc function, and new keyword).

1. When a process exits, it must release its memory. How could it release memory that
contains its heap intertwined with some other processes heap?

3. no, see 1.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

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Re: heap

George_George10-Nov-07 23:40

George_George

10-Nov-07 23:40

Thanks Luc,

Could you help to show some practical usage of creating private heap please?

regards,
George

Re: heap

Luc Pattyn11-Nov-07 3:18

Luc Pattyn

11-Nov-07 3:18

Hi,

Having more than one heap may improve the memory situation (less fragmentation)
and the performance.

PERFORMANCE

You could take advantage of a private heap like this:
- create a private heap
- allocate a lot of objects on that heap
- when done, rather than freeing each of these objects, and then the heap itself,
you can free the heap directly without caring about the objects it contains; this of course
assumes you don't need the objects any longer.

FRAGMENTATION

Example: a program needs a lot of type1 objects for a long time and a lot of type2 objects
for a short time; these objects are created at the same time.

First scenario: using a single heap the objects would get interleaved somehow, so freeing the type2 objects would leave the one heap fragmented, effecively not yielding free memory pages
at all.

Second scenario: allocating type1 objects on heap1 and type2 objects on heap2, when done
with type2, heap2 can be freed, effectively freeing all its memory pages whereas heap1
continues to be used (with less, at best no, fragmentation).

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

this months tips:
- use PRE tags to preserve formatting when showing multi-line code snippets
- before you ask a question here, search CodeProject, then Google

Re: heap

George_George11-Nov-07 3:37

George_George

11-Nov-07 3:37

Thanks Luc,

Practical and excellenet!

regards,
George

ALT code

V_shr9-Nov-07 23:29

V_shr

9-Nov-07 23:29

hi all, i wanted to simulate pressing ALT by keybd_event() but i dont know the code , or if it is a virtual key. does any1 know code or virtual_key value?
thnx

Re: ALT code

dtr110-Nov-07 0:01

dtr1

10-Nov-07 0:01

WM_SYSKEYDOWN.If u use it in PreTranslateMessage:

BOOL CTest::PreTranslateMessage(MSG* pMsg)
{
if (pMsg->message == WM_SYSKEYDOWN && pMsg->wParam == VK_..something..)
{
// TO DO:....
}
return CDialog::PreTranslateMessage(pMsg);
}

Re: ALT code

V_shr10-Nov-07 0:11

V_shr

10-Nov-07 0:11

lol,i wanted the something in "VK_something" , my question's answer is : the alt code is (for example) VK_ALT ! or something like that , i know how to get other keys like VK_Shift , but there is nothing about ALT key in my book Frown | :(

Re: ALT code [modified]

dtr110-Nov-07 0:25

dtr1

10-Nov-07 0:25

I answered WM_SYSKEYDOWN if you use it in PreTranslateMessage, not VK_something. But you want to simulate.

-- modified at 6:43 Saturday 10th November, 2007

Re: ALT code

V_shr10-Nov-07 0:40

V_shr

10-Nov-07 0:40

i want to press the alt not to check if it is pressed or not . Big Grin | :-D

thnx , V_shr

Re: ALT code

dtr110-Nov-07 0:49

dtr1

10-Nov-07 0:49

use this: keybd_event(VK_MENU,0xb8,0,0);

Re: ALT code

dtr110-Nov-07 0:54

dtr1

10-Nov-07 0:54

Don't forget to release the ALT key with :

keybd_event(VK_MENU,0xb8,KEYEVENTF_KEYUP,0);

Re: ALT code

V_shr10-Nov-07 1:04

V_shr

10-Nov-07 1:04

thanks a LOT Big Grin | :-D

Two dimensional array

George_George9-Nov-07 22:22

George_George

9-Nov-07 22:22

Hello everyone,

I am just interested in the following sample, how compiler maps one dimensional int pointer array to two dimensional int array so perfect. E.g. p [3][3] maps to the 33th element and p [0][9] maps to the 9th element.

How does the compiler do the internal mapping of one dimensional int pointer array (variable p) and the two dimensional int array (variable buffer)?

<br />
int main (int argc, char** argv)<br />
{<br />
<br />
	int (*p) [10];<br />
	int buffer [10][10];<br />
	int tmp;<br />
	int i = 0;<br />
	int j = 0;<br />
<br />
	// to initialize<br />
	for  (i = 0; i < 10; i++)<br />
	{<br />
		for (j = 0; j < 10; j++)<br />
		{<br />
			buffer [i][j] = i * 10 + j;<br />
		}<br />
	}<br />
<br />
	p = &buffer;<br />
<br />
	tmp = p [3][3]; // tmp = 33<br />
<br />
	tmp = p [0][9]; // tmp = 9<br />
<br />
	return 0;<br />
}<br />

thanks in advance,
George

Re: Two dimensional array

chandu0049-Nov-07 23:53

chandu004

9-Nov-07 23:53

sorry to say that, right now, i donot have any idea on this post,
but how about your algorithm to get 1000 largest values? any good news?
here i have implemented the algorithm as i suggested, using linked lists.
it took 30 seconds to sort 10 crore samples.
do you want me to share it?
or have you got a better idea to implement it.

Re: Two dimensional array

George_George10-Nov-07 0:13

George_George

10-Nov-07 0:13

Hi chandu004,

I decide to use nth_element to do the preliminary implementation. Currently, I am writing some code to parse the data into memory based data structure.

http://en.wikipedia.org./wiki/Selection_algorithm[^]

regards,
George

Re: Two dimensional array

chandu00410-Nov-07 0:16

chandu004

10-Nov-07 0:16

how much time does your nth element logic take to sort the elements?

Re: Two dimensional array

George_George10-Nov-07 0:28

George_George

10-Nov-07 0:28

Hi chandu004,

chandu004 wrote:
how much time

How much time you mean the elapsed time of one invocation of nth_element or how many times I invoke function nth_element?

regards,
George

Re: Two dimensional array

chandu00410-Nov-07 0:34

chandu004

10-Nov-07 0:34

time to take out top 1000 elements from 10 crore elements.

Re: Two dimensional array

George_George10-Nov-07 0:38

George_George

10-Nov-07 0:38

Thanks for your interest and attention, chandu004.

I will tell you the result when I complete the draft coding, currently I am writing the parser to read data into memory.

regards,
George

Re: Two dimensional array

chandu00410-Nov-07 1:06

chandu004

10-Nov-07 1:06

i have put my algorithm here
[^]
please refer it.

--------------------------------------------
Suggestion to the members:
Please prefix your main thread subject with [SOLVED] if it is solved.
thanks.
chandu.

Re: Two dimensional array

George_George10-Nov-07 3:07

George_George

10-Nov-07 3:07

Cool chandu,

I must study your code and post my code when I complete the parser code.

regards,
George

Re: Two dimensional array

Mark Salsbery10-Nov-07 5:56

Mark Salsbery

10-Nov-07 5:56

The compiler does it the same way you do when you initialize the
array.

A pointer to the indexed array element is formed by multiplying the indexes
by the associated array dimension(s). In your example, to get the
value in the array at p[x][y], the compiler creates code to calculate
a pointer to the value

tmp = p [x][y];
ptrtovalue = ptrtoarraystart + ((x * arraydimension1 + y) * sizeof(int))
tmp is asigned the int found at ptrtovalue

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

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