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Tutorials, books, programming, programming, programming (get a decent, updated compiler, e.g. g++).
You might easily find many many resources freely available on the web, Google is your friend.
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I have CListCtrl and updating this control with love data using OnTimer(). But i want to select some rows and do furthur actions. But when i select the row, the selected color appears,but moment it updating using OnTimer(), the selected row color become normal. How can i keep the selection row visible always?
Anu
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Store the selected item index (or, maybe, item data) before the updating the list.
After update select the stored item.
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Hi All,
I'm trying to create a C++ DLL using the WinInet API, but for some odd reason, I get no errors during compiling but get external link errors regarding variables within my class. Any idea how I can resolve this? Visual Studio 2015.
----------------------------------------header test.h -------------------------------------------
// #include "stdafx.h"
using namespace std;
// #include <Winineti.h>
#include <windows.h>
#include <strsafe.h>
#include <wininet.h>
#include <math.h>
#include <cstring>
#include <WinInet.h>
//#include <string>
#pragma comment(lib, "wininet.lib")
#pragma comment(lib, "user32.lib")
#define FTP_FUNCTIONS_BUFFER_SIZE MAX_PATH+8
namespace Win32_FTP
{
class FTP_Win32_ClientV1
{
private:
public:
static LPCWSTR sFileSearch;
static char * sIpAddress;
static LPCWSTR sUsername;
static LPCWSTR sPassword;
static string sRemoteDir;
static string sLocalDir;
static string sFilename;
static DWORD dwError;
static HINTERNET hFTPConnect;
static HINTERNET hFind;
static HINTERNET hConnect;
static HANDLE hFile;
static WIN32_FIND_DATA FindFileData;
static string strTemp;
static __declspec(dllexport) void Test1();
static __declspec(dllexport) void FtpCloseConnection();
};
}
----------------------------------------source test.cpp -------------------------------------------
//using namespace std;
#include <iostream>
#include "test.h"
// using namespace std;
namespace Win32_FTP
{
void FTP_Win32_Client::Test1()
{
cout << "This is a test from Cplus to Csharp DLL";
}
void FTP_Win32_Client::FtpCloseConnection()
{
InternetCloseHandle(FTP_Win32_Client::hFind);
InternetCloseHandle(FTP_Win32_Client::hFTPConnect);
InternetCloseHandle(FTP_Win32_Client::hConnect);
}
}
***************************LINK ERRORS ************************
Test.obj : error LNK2001: unresolved external symbol "public: static void * Win32_FTP::FTP_Win32_Client::hFTPConnect" (?hFTPConnect@FTP_Win32_Client@Win32_FTP@@2PAXA)
Test.obj : error LNK2001: unresolved external symbol "public: static void * Win32_FTP::FTP_Win32_Client::hFind" (?hFind@FTP_Win32_Client@Win32_FTP@@2PAXA)
Test.obj : error LNK2001: unresolved external symbol "public: static void * Win32_FTP::FTP_Win32_Client::hConnect" (?hConnect@FTP_Win32_Client@Win32_FTP@@2PAXA)
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Class static variables, like Win32_FTP::FTP_Win32_Client::hFTPConnect must be also defined in one source file. That is you have to write
HINTERNET Win32_FTP::FTP_Win32_Client::hFTPConnect; (and so on...) in your test.cpp source file.
An altrernative, available only with C++ 17 compliant compilers is to declare such variables inline inside the header file (see, for instance INLINE VARIABLES[^]).
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Why are you creating a class and then making everything static?
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Definitely remove the line: using namespace std;
My advice: NEVER do that.
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There is Base class A which has child's B, C, D, ... Z.
I need to add some methods to Z as virtual ones so that they will be overridden in Z child classes Z1, Z2, .. Zn.
Is it possible, how can I do it.
Note: I cannot add to base class A.
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Start by telling us why you need to add the virtual methods. And why you can't add to the base class A.
The difficult we do right away...
...the impossible takes slightly longer.
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Well I have over 50 classes there. All of them have base class the same.
Those functions (about 20 functions) are needed only for my one 5 level class (Class A5 : public A4) and two 6 level child classes ( Class A61 : public A5 and Class A62 : public A5).
Reason because I want to make one handler class which will use A5 class virtual functions and will handle A61 and A62.
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Quote: I need to add some methods to Z as virtual ones so that they will be overridden in Z child classes Z1, Z2, .. Zn.
Is it possible, how can I do it.
Yes it is possible. Just do it.
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You might not need to make them virtual.
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Just learning OpenMP.
So what is , if any , the difference between "processor" / CPU or "thread"?
They seems to be used interchangeably.
And do I have to specify # of processors / threads to be actually used by the app?
I suppose I can also select which part of code will be "multi x", but that is irrelevant for now.
int iCPU = 0;
iCPU = omp_get_num_procs();
cout << "# of CPU's " << dec << +iCPU << endl;
omp_set_num_threads(iCPU);
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Initially for the application will set the number of threads = nofCores, as 1 thread per core will get you the best performance.
From there your performance goes down for both other options
Sometime you don't want all the cores doing stuff so you control it and you will run across things like
#pragma omp parallel num_threads(3)
{
... some code for 3 cores
}
Then you get the other option multiple threads per core ... that involves context switching so again performance loss.
So it starts that way on initial easy samples but it won't stay that way for very long 
In vino veritas
modified 9-Feb-19 4:08am.
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Processors or CPUs mean the same thing. They are the hardware devices (or parts of a chip) that execute the instructions in a program. Processes or Threads, are activities that can run inside a processor. A thread is simply a discrete set of instructions that are executed by the CPU. Some applications run quite happily with a single thread. Others require multiple threads in order to perform different parts of the program in parallel. However, using multiple threads is not always the most efficient way to run an application, since a single CPU (or 'core' in a modern chip) can only run one thread at a time. So if you have a four-core chip you can run four threads in parallel with reasonable efficiency. With a single core it would probably not be very efficient owing to operating system overhead to manage switching between threads. Unless you really need threads, and fully understand the concept and practicalities of them, they are best avoided.
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So the example I used retrieves # of processors / CPU hardware and sets the # of threads per each processor / CPU equal to # of processors / CPU hardware.
Does not make much sense.
The way I read the example - it really does not tell me how many processors / CPU hardware will be utilized.
Perhaps I need to read the OpenMP doc.
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I do not know exactly what you are trying to achieve here. Maybe the documentation makes it clear.
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My objective is for the app to utilize ALL hardware processors / CPU.
From posts so far I feel I do not need multiple threads running in each CPU, one will do for now.
I am just trying to understand the relations between processors and threads.
The following code leads to believe that the threads are NOT related to # of processors.
int iCPU = 0;
iCPU = omp_get_num_procs();
cout << "# of CPU's " << dec << +iCPU << endl;
gets "4" which is number of CPU's
int iMAXThread = 0;
iMAXThread = omp_get_max_threads();
cout << "# of iMAXThread " << dec << +iMAXThread << endl;
also gets "4" - apparently default of "one thread to CPU ?"
// Now set the number of threads
omp_set_num_threads(10);
iMAXThread = omp_get_max_threads();
returns "10" per "system ?"
cout << "# of iMAXThread " << dec << +iMAXThread << endl;
exit(1);
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I'd recommend you google for "openmp tutorial C++" and work through one or more of them. I don't know anything about OpenMP, except that its a MultiProcessing (i.e. threading) extension to C/C++. I do know that multi-threading is easy to get wrong. Added to which, having multiple threads means that you get out-of-order (to the human brain, anyway) execution, which can lead to unexpected results e.g. (the following code comes from one of the tutorials ... don't ask me anything further about it!)
<div class="op">Quote:</div>$ cat example.c
#include <omp.h>
#include <stdio.h>
int main()
{
#pragma omp parallel
{
int ID = omp_get_thread_num();
printf("hello(%d)", ID);
printf("world(%d)\n", ID);
}
return 0;
}
$ gcc -fopenmp example.c -o example
$ ./example
hello(1)world(1)
hello(0)world(0)
hello(3)world(3)
hello(2)world(2)
$ ./example
hello(3)world(3)
hello(0)world(0)
hello(1)world(1)
hello(2)world(2)
$ ./example
hello(3)world(3)
hello(2)hello(1)world(1)
hello(0)world(0)
world(2)
That's about as simple as a MP program gets, and you can see that
a) the threads didn't run in the same order every time, and
b) in the last run thread(2) was interrupted by thread(1) and thread(0) before it completed.
Proceed with caution!
modified 9-Feb-19 14:37pm.
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I'd also like to point out that with threads, debugging becomes more challenging, too!
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I really appreciate all contributions to this thread so far.
As anything "new" to me I do not have any specific / planned way to proceed with my learning , especially to cover some of the less obvious / less visible aspects.
I do however maintain that learning new technology is not always "from bottom up" , it is a mosaic / puzzle whose pieces by itself do not make much sense.
Let me restate my "objective" in using OpenMP - utilize ALL CPU's available in the application.
I have deliberately NOT specified WHAT the app does. My objective should be descriptive enough.
But to attempt to refine the "puzzle" , and for those curious, I do not foresee any future applications critical in sequence of how the app is executed.
I still believe that utilizing all hardware CPU's will eventually benefit the app, but honestly I am not interested in proving / disproving that in any specific way.
As far as OpenMP "tutorials" - it is very mature technology and most of the tutorials reflect that. And some of them are just repetitious in the cautioning the reader in "difficulties " of debugging multi threaded applications.
Cheers
Vaclav
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OpenMP works out how many CPU core you have at runtime.
It isn't a fixed answer and there may be cores unavailable to you and there isn't a thing you can do about it.
This call returns the number of cores available to you at time of call
int omp_get_num_procs();
Inside Windows or Linux certain threads may have a core locked with core affinity and you can sit there and whistle dixie the OS is never going to give OpenMP that core.
OpenMP is not the OS and is not in control of core scheduling it asks and locks the maximum the O/S will allow.
So if you aren't getting all the cores you need to look at the O/S level.
google something like "Affinity control outside OpenMP"
In vino veritas
modified 9-Feb-19 22:59pm.
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Thanks Leon.
Found this and my first impression is that simple "Hello world" MAY be better way to get more familiar with OpenMP. Just "adding OpenMP" to my existing code is not going to tell me if it is doing anything useful until I add some controls / measurements / trace.
That is contrary to my initial statement that I am not interested in analyzing OpenP processes, but to do that I need more experience with OpenMP.
Error[^]
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I would suggest you need a better understand of threads, and some practical experience of using them. Without understanding the basics, I doubt that OpenMP is going to bring you any benefit.
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