C / C++ / MFC

28-Apr-04 6:58

Im creating threads and I want to pass a pointer to the threads, Is is possible to cast a pointer to a class into a DWORD, if so, how is it done???
Here is the code Im working with, its taken straight from the MSDN

void main(void){<br />
<br />
DWORD loadPerThrdID;<br />
HANDLE loadPerThrd;<br />
TCHAR szMsg[80];<br />
<br />
DWORD dwThrdParam; <br />
	<br />
static WmiWrapper Wmi(NULL, NULL, NULL); //Creating object<br />
<br />
loadPerThrd = CreateThread(<br />
	        NULL, 0, <br />
		loadPerThrdFunc,<br />
		&dwThrdParam,<br />
		0, &loadPerThrdID);<br />
		<br />
if(loadPerThrd == NULL){<br />
	wsprintf(szMsg, (TEXT("Create Thread failed for LoadPercentage")));<br />
	MessageBox(NULL, szMsg, NULL, MB_OK);<br />
}<br />
else{<br />
	_getch();<br />
	CloseHandle(loadPerThrd);<br />
}<br />
}<br />
<br />
//Threads function<br />
DWORD WINAPI loadPerThrdFunc (WmiWrapper Wmi)<br />
{<br />
................<br />
}

What can I do to get this to work, or am I completly out??????

David Crow28-Apr-04 7:19

28-Apr-04 7:19

roadragedave wrote:
Is is possible to cast a pointer to a class into a DWORD, if so, how is it done???

Both a pointer and a DWORD are 32-bit values.

DWORD WINAPI loadPerThrdFunc( LPVOID param )
{
    DWORD *p = (DWORD *) param;
    TCHAR s[32];
    wsprintf(s, "The thread value is %lu\n", *p)
    MessageBox(s);
}

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

roadragedave28-Apr-04 8:31

28-Apr-04 8:31

Im still lost,
You said that pointers and DWORD are 32 bits, but when I build the app, the following line warnss me that there is a possible mismatch

DWORD dwThrdParam = UINT_PTR(&Wmi);

gives me:

warning C4244: 'initializing' : conversion from '__w64 unsigned int' to 'DWORD', possible loss of data

but otherwise it passes fine, but how do I turn the parameter LPVOID param back into the object or at least a pointer to the object????

We have a mathematician, a different kind of mathematician, and a statistician!

David Crow28-Apr-04 8:52

28-Apr-04 8:52

roadragedave wrote:
You said that pointers and DWORD are 32 bits...

Most of the time they are. You are apparently doing some 64-bit work.

DWORD dwThrdParam = (DWORD) UINT_PTR(&Wmi); // potential loss of data
or
__w64 dwThrdParam = UINT_PTR(&Wmi);

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

roadragedave28-Apr-04 8:55

28-Apr-04 8:55

Excellent stuff, that got rid of the warning, but again how, do I change it back inside the thread function

We have a mathematician, a different kind of mathematician, and a statistician!

David Crow28-Apr-04 9:00

28-Apr-04 9:00

Was the example I provided earlier incorrect? If so, how is CreateThread() currently being called, and what does your thread function currently look like?

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

roadragedave28-Apr-04 9:11

28-Apr-04 9:11

But how, by using this:

DWORD WINAPI loadPerThrdFunc( LPVOID param )<br />
{    DWORD *p = (DWORD *) param;    <br />
     TCHAR s[32];    <br />
     wsprintf(s, "The thread value is %lu\n", *p)    <br />
     MessageBox(s);<br />
}

can I get to call the methods of the WmiWrapper class Wmi

Im calling the CreateThread method like so:

DWORD loadPerThrd = CreateThread(<br />
              NULL, 0, <br />
              loadPerThrdFunc,<br />
              &dwThrdParam,<br />
              0, &loadPerThrdID);

We have a mathematician, a different kind of mathematician, and a statistician!

David Crow28-Apr-04 9:15

28-Apr-04 9:15

DWORD loadPerThrd = CreateThread(
    NULL, 0, 
    loadPerThrdFunc,
    &Wmi,
    0, &loadPerThrdID); 
 
DWORD WINAPI loadPerThrdFunc( LPVOID param )
{ 
    WmiWrapper *p = (WmiWrapper *) param; 
    p->...
}

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

roadragedave28-Apr-04 9:24

28-Apr-04 9:24

Fantastic!!!!

We have a mathematician, a different kind of mathematician, and a statistician!

Michael Dunn28-Apr-04 14:05

Michael Dunn

28-Apr-04 14:05

CreateThread() has a param just for this purpose: void* lpParameter. Set that to the address of the Wmi object. loadPerThrdFunc takes one parameter, again a void*, which you cast back to a WmiWrapper*

Note that you should be using _beginthreadex() and not CreateThread() if you link with the C runtime (which you probably are)

--Mike--
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----
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Jitendra gangwar28-Apr-04 19:05

Jitendra gangwar

28-Apr-04 19:05

Did some modification in your existing code. This would help you.
For the passing parameter to thread, first cast it to DWORD and receive it in callback handler of thread,cast it back to its original type,now use it as you want.

void main(void){

DWORD loadPerThrdID;
HANDLE loadPerThrd;
TCHAR szMsg[80];

DWORD dwThrdParam;

static WmiWrapper Wmi(NULL, NULL, NULL); //Creating object

loadPerThrd = CreateThread(
NULL, 0,
loadPerThrdFunc,
//&dwThrdParam,
(DWORD) &Wmi, //Pass the object pointer as a thread parameter.
0, &loadPerThrdID);

if(loadPerThrd == NULL){
wsprintf(szMsg, (TEXT("Create Thread failed for LoadPercentage")));
MessageBox(NULL, szMsg, NULL, MB_OK);
}
else{
_getch();
CloseHandle(loadPerThrd);
}
}

//Threads function
DWORD WINAPI loadPerThrdFunc (DWORD param1)
{
WmiWrapper* wmi = (WmiWrapper*) param1;
//Now you can use this wmi class pointer.
................
}

Jitendra

roadragedave28-Apr-04 22:58

28-Apr-04 22:58

No good,
First I think the WmiWrapper* is 64 bits, where as DWORD is 32, so this gives me data loss warnings,
Also the parameter is LPTHREAD_START_ROUTINE, not DWORD, so this gives me an error.

Its alright because I have it fixed (see David Crows code above), but now Im getting a memory voilation when running, and its in one of the classes methods, I dont understand, because I was running the program without threads before and I didnt get this problem, I thought mabey it has something to do with the fact that Im creating two threads which pass the same object, but if I turn off one I still get the error Confused | :confused:

We have a mathematician, a different kind of mathematician, and a statistician!

Paul Ranson28-Apr-04 23:36

Paul Ranson

28-Apr-04 23:36

The 'WmiWrapper*' can only be 64 bits if you're compiling for 64 bit Windows. You would know this.

I think you get the warning because MS have made the SDK headers 64 bit compatible and introduced some new MS special bits to allow this. In the future a DWORD won't be compatible with a pointer.

Anyway the parameter to CreateThread is 'LPVOID' not DWORD so in 64bit Windows that will be a 64 bit pointer and all will just work.

Anyway I would expect something like

DWORD WINAPI loadPerThrdFunc ( LPVOID param )
{
    WmiWrapper* wmi = reinterpret_Cast<WmiWrapper*>( param ); 
    //...
}
//...
loadPerThrd = CreateThread (
    NULL,
    0, 
    loadPerThrdFunc,
    &Wmi,
    0,
    &loadPerThrdID);

Paul

how can i dynamically get my machine ip address ?

Jitendra gangwar29-Apr-04 1:33

Jitendra gangwar

29-Apr-04 1:33

That is all right.Thanks for correcting me.
The memory violation that you are facing may be due to that you are creating a local object.when you are creating the thread and passing the pointer of it. but after creation of thread, the control come back in the main function and the local object will got out of scope.still the thread is running and trying to access it by the pointer and cause the memory violation. if this is a problem then you can allocate the object by 'new' operator. so when you don't want it you can deallocate it manually.

Jitendra

Marco M.28-Apr-04 6:17

Marco M.

28-Apr-04 6:17

i need to get the ip of the machine my code is running on..
how can i program that ?
thanx

shakoosh

Re: how can i dynamically get my machine ip address ?

David Crow28-Apr-04 7:03

Re: how can i dynamically get my machine ip address ?

28-Apr-04 7:03

Call gethostname() followed by gethostbyname().

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

toxcct28-Apr-04 7:09

toxcct

28-Apr-04 7:09

you can list all your IP Addresses by doing this :

<font style="color:blue;">struct</font> hostent* infohost;
<font style="color:blue;">char</font> HostName[256];
<font style="color:blue;">char</font>** addrs;
<font style="color:blue;">char</font>* Host;
 
gethostname(HostName, 255);
Host = HostName;
infohost = gethostbyname(HostName);
addrs = infohote -> h_addr_list;
<font style="color:blue;">while</font> (*addrs) {
    printf("IP : %s\n", inet_ntoa( *(struct in_addr *)* addrs));
    addrs++;
}

don't forget to check errors.
Your main IP Address while being in a TCP network is in general the first, but not necessarily...

TOXCCT >>> GEII power

Re: how can i dynamically get my machine ip address ?

RNEELY28-Apr-04 8:16

RNEELY

28-Apr-04 8:16

<br />
// GetMyManagedIP.cpp<br />
#include "stdafx.h"<br />
#using <mscorlib.dll><br />
#using <System.Windows.Forms.dll><br />
using namespace System;<br />
using namespace System::Windows::Forms;<br />
<br />
int _tmain(int argc, _TCHAR* argv[])<br />
{<br />
  String* hostName = SystemInformation::ComputerName;<br />
  System::Net::IPHostEntry* hostEntry = System::Net::Dns::GetHostByName(hostName);<br />
  Console::WriteLine(S"Host name : {0}", hostEntry->HostName);<br />
  for (System::Int32 i = 0; i < hostEntry->AddressList->Length; ++i)<br />
  {<br />
    Console::WriteLine(hostEntry->AddressList->Item[i]);<br />
  }<br />
  return 0;<br />
}<br />

Sincerely,
-Ron

Re: how can i dynamically get my machine ip address ?

RNEELY28-Apr-04 9:09

RNEELY

28-Apr-04 9:09

Or, if you don't like console output:

<br />
// GetMyManagedIP.cpp<br />
#include "stdafx.h"<br />
#using <mscorlib.dll><br />
#using <System.Windows.Forms.dll><br />
using namespace System;<br />
using namespace System::Windows::Forms;<br />
<br />
int _tmain(int argc, _TCHAR* argv[])<br />
{<br />
#pragma push_macro("new")<br />
#undef new<br />
  String* hostName = SystemInformation::ComputerName;<br />
  System::Net::IPHostEntry* hostEntry = System::Net::Dns::GetHostByName(hostName);<br />
  for (int i = 0; i < hostEntry->AddressList->Length; ++i)<br />
  {<br />
	Text::StringBuilder* sb = new Text::StringBuilder();<br />
	sb->Append(hostName);<br />
	sb->AppendFormat(S" IP Address {0} = ", __box(i));<br />
	sb->Append(hostEntry->AddressList->Item[i]->ToString());<br />
	MessageBox::Show(sb->ToString());<br />
  }<br />
  return 0;<br />
#pragma pop_macro("new")<br />
}<br />

Sincerely,
-Ron

Frequent open/close registry key?

Gibson_66628-Apr-04 5:48

Gibson_666

28-Apr-04 5:48

I got a question regarding storing of settings in the registry.
My application continously stores settings in the registry during runtime, before each value is saved I open the specific registry key and after the value is saved operation i close it.
This causes a frequent opening and closing of a specific registry key.
Is it more suitable for my application to open the registry key at start and to close the key whenever my application is due to shut down? Will there be somekind of vulnerability/benefit using this method, which one is prefered?

Re: Frequent open/close registry key?

David Crow28-Apr-04 7:10