Re: Which is better? - C / C++ / MFC Discussion Boards

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Re: Which is better?

Tim Smith19-Aug-06 14:13

Tim Smith

19-Aug-06 14:13

That isn't true.

Depending on the scope, declaring a variable such as "CMyClass myInstance;" can exist for the life of the program (if declared in a global scope or as a static method/function variable), exist for the life of a containing class or when used inside a method or function, exist for the life of the scope in the functoin.

In general, declaring things such a "CMyClsas myInstance" is much better than declaring them on the heap. You don't have to worry about memory allocation but you do have to worry about object lifetime.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Re: Which is better?

xxrl18-Aug-06 21:27

xxrl

18-Aug-06 21:27

hi I recommend to try the second usage.but if you have poor memory manage techology,you have to use the first usage.

For the two usage,you have to process every point exception and create a steady program.

You are the best!Me too!

Re: Which is better?

Naveen18-Aug-06 21:29

Naveen

18-Aug-06 21:29

xxrl wrote:
I recommend to try the second usage

why u say so. Any reason for this?

nave

Re: Which is better?

Don Fletcher20-Aug-06 23:24

Don Fletcher

20-Aug-06 23:24

I have found that using dynamic memory allocation is always preferable, because some of the Microsoft MFC code contains the line:

delete this;

This will cause an exception if such a window or control is declared on the stack, and from experience it can be very frustrating to locate the source of the failure when it happens.

Re: Which is better?

Naveen21-Aug-06 0:58

Naveen

21-Aug-06 0:58

do u believe Microsoft people are so foolish to do that?:->

Can u say an example...?

They might have wrote such a code because they will be that much sure that the "Object" is created in the heap.

nave

Re: Which is better?

Tim Smith19-Aug-06 14:10

Tim Smith

19-Aug-06 14:10

Using the heap (i.e. new) instead of the stack can cause all sorts of performance problems due to the memory manager. However, large objects (for example, something over 20k) might cause problems if allocated on the stack.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Re: Which is better?

Kevin McFarlane19-Aug-06 9:19

Kevin McFarlane

19-Aug-06 9:19

Generally you should declare objects on the stack unless you need to declare them on the heap. If you do declare them on the heap consider using a smart pointer.

Kevin

Re: Which is better?

HakunaMatada20-Aug-06 18:30

HakunaMatada

20-Aug-06 18:30

Thanks...

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Re: Which is better?

Hamid_RT22-Aug-06 6:59

Hamid_RT

22-Aug-06 6:59

See Dynamic Memory[^]

WhiteSky

Linker error

Anu_Bala18-Aug-06 19:54

Anu_Bala

18-Aug-06 19:54

Hi,I got this error when i rebuild my coding.Im working with this coding,when i just run this coding it does not show this error,finally when i rebuild this to get EXE i got this error..
Linking...
nafxcwd.lib(afxmem.obj) : error LNK2005: "void * __cdecl operator new(unsigned int)" (??2@YAPAXI@Z) already defined in Communciation.obj
.\Debug/CS3OperatorStation.exe : fatal error LNK1169: one or more multiply defined symbols found
Error executing link.exe.
I used unsigned int only in one class in TagInfo.cpp not in communication.cpp..I am using unsigned int in these four lines only..

unsigned int CTagAlrmLgt::GetColor(int iNo)
unsigned int nTopColor;
unsigned int nBotColor;
unsigned int GetColor(int);

Please help me out to find the error..

Anu

Re: Linker error

Naveen18-Aug-06 20:00

Naveen

18-Aug-06 20:00

have u over loaded the new operator?

nave

Re: Linker error

Sarath C18-Aug-06 21:10

Sarath C

18-Aug-06 21:10

see the general rules for operator overloading.[^]

SaRath.

"Before you can learn to recognize what's wrong, you must learn to recognize what's right" - Raymond Chen."

My Blog | Understanding State Pattern

Vitual key, VS2005 [modified] solved

NorGUI18-Aug-06 19:42

NorGUI

18-Aug-06 19:42

Hello,
I have a application SDI that use also other dialog modless. I would like use a vitual key (like F4) to do something. It works only when the main appliccation have a focus but not when a other dialog from the same application. What can I try to make that possible.

Thank you !! I have tryed and it works Laugh | :laugh:

-- modified at 2:46 Monday 21st August, 2006

AutreChien

Re: Vitual key, VS2005

Naveen18-Aug-06 19:57

Naveen

18-Aug-06 19:57

u must map the WM_KEYDOWN in the PreTranslateMessage() function of app class like this

BOOL CSdiApp::PreTranslateMessage(MSG* pMsg) <br />
{<br />
	if( WM_KEYDOWN == pMsg->message )<br />
	{<br />
         if( pMsg->wParam== VK_F4)<br />
         {<br />
             AfxMessageBox( _T("f4 pressed"));<br />
         }<br />
         <br />
	}<br />
	return CWinApp::PreTranslateMessage(pMsg);<br />
}

nave

Re: Vitual key, VS2005

Justin Tay19-Aug-06 2:37

Justin Tay

19-Aug-06 2:37

Try Global Hot Keys[^].

STL Map.find()

shadrach_india18-Aug-06 19:38

shadrach_india

18-Aug-06 19:38

I am struggling with find() of map for last 15 day, my target is reading EVENTLOGRECORD from all machine at a time (with help of multithread ) and doing some processes on the information and writing to a separate file for each machine. It is working fine for a machine at a time. if I I read more than one machine for > 4 hours data from the machine, the map.find() giving exception . it is not frequently happening

What will be the error ?

My code
map<string ,cevent="" *=""> m_eventlist;
map<string,cevent *="">::iterator m_iter;

m_useriter=m_userlist.find(newkey); -

CEvent is a user defined object

thanks

Re: STL Map.find()

Stephen Hewitt20-Aug-06 16:07

Stephen Hewitt

20-Aug-06 16:07

I would guess this is because you're accessing the map (and likely other things) from multiple threads without synchronization. Multithreaded programming is hard.

Steve

Previewing many pages

mikobi18-Aug-06 19:09

mikobi

18-Aug-06 19:09

Dear Sir,
I am using Roger Allen Preview Extension to do PrintPreview.

I have a file that I need to Preview all records and i make a loop on OnpreparePrinting to do So, I see only the last page, all previous I don't see it.

My problem perhaps is that I did n't yet use Doc/View printing, I do only printing with non Doc/View facility.

Who can help me ?

Drawing on the window [modified]

ramanand_bulusu18-Aug-06 18:38

ramanand_bulusu

18-Aug-06 18:38

hi,
Here i have one probleme regarding VC++,if anyone know the solution plz give me the suggetions.the problem is that i have written a programe to diaplay the Rectangle.Now if i want to change the size of the Rectangle and move it Position of the Rectangle through mouse what i have to do?

bulusu ramanand

-- modified at 0:46 Saturday 19th August, 2006

Re: Drawing on the window

Hamid_RT18-Aug-06 19:33

Hamid_RT

18-Aug-06 19:33

See Multiple CRectTracker Class[^] and here[^]

WhiteSky

Ask a unsolved problem for long time

begtostudy18-Aug-06 16:38

begtostudy

18-Aug-06 16:38

I have 3 projects in workspace.I use VC 6.0.

project DipApi is a win32 static Library
They are all functions.

project CDib is MFC extension DLL,and use DibApi.lib
It will export a class.These is the header file Dib.h of the class,below
#include "..\DibApi\DIBAPI.H"
class AFX_EXT_CLASS CDib : public CObject
{
DECLARE_SERIAL(CDib) //serialization
......

export dll is ok.

CDibEx also is a MFC extension DLL project,use DibApi.lib too,and the upper class.
It will export a class too.These is the header file DibEx.h of the class,below
#include "..\dibapi\dibapi.h"
#include "..\cdib\Dib.h"
//This is the upper header file.I do not know whether to change it.
#define EFFECT_SCANDOWN 1
#define EFFECT_SCANUP 2
#define EFFECT_SCANRIGHT 3
class AFX_EXT_CLASS CDibEx : public CDib
{
DECLARE_SERIAL(CDibEx) //serialization
... ...
but ,when building,VC show:
Creating library Debug/CDibEx.lib and object Debug/CDibEx.exp
DibEx.obj : error LNK2001: unresolved external symbol "public: static struct CRuntimeClass

CDib::classCDib" (?classCDib@CDib@@2UCRuntimeClass@@A)
Debug/CDibEx.dll : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

Look for AFX_EXT_CLASS in MSDN.In Export and Import Using AFX_EXT_CLASS,it has
"For example, the DECLARE_DYNAMIC macro is defined as follows when building an extension

DLL:

#define DECLARE_DYNAMIC(class_name) \
protected: \
static CRuntimeClass* PASCAL _GetBaseClass(); \
public: \
static AFX_DATA CRuntimeClass class##class_name; \
virtual CRuntimeClass* GetRuntimeClass() const; \

The line that begins with static AFX_DATA is declaring a static object inside of your

class. To export this class correctly and access the run-time information from a client

executable, you must export this static object. Because the static object is declared with

the modifier AFX_DATA, you only need to define AFX_DATA to be __declspec(dllexport) when

building your DLL and define it as __declspec(dllimport) when building your client

executable. Because AFX_EXT_CLASS is already defined in this way, you just need to

redefine AFX_DATA to be the same as AFX_EXT_CLASS around your class definition.

For example:

#undef AFX_DATA
#define AFX_DATA AFX_EXT_CLASS

class CExampleView : public CView
{
DECLARE_DYNAMIC()
// ... class definition ...
};

#undef AFX_DATA
#define AFX_DATA

"

I am sorry for knowing unclearly,so I did know whether it relate to my problem.
Actually,I want to make two class to dlls respectively.
But I don't know where I was wrong.Please tell me ,thanks a lot!

begtostudy

Re: Ask a unsolved problem for long time

begtostudy19-Aug-06 20:40

begtostudy

19-Aug-06 20:40

http://msdn.microsoft.com/library/en-us/vccore/html/_core_Mutual_Imports.asp

I solved by myself！

problems with recvfrom

afpr18-Aug-06 13:36

afpr

18-Aug-06 13:36

Hello,

I'm don't receive any packet with winsock program.

My code is:

SOCKET RecvSocket,SendSocket;
int ReceiverAddrSize = sizeof(RecvAddr);

RecvSocket = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
SendAddr.sin_family = AF_INET;
SendAddr.sin_port = htons(Port);
SendAddr.sin_addr.s_addr = htonl(INADDR_ANY);
length = recvfrom(RecvSocket, SendBuf, BufLen, 0, (SOCKADDR *) &RecvAddr, &ReceiverAddrSize);
if (length == -1) {
printf("ERRO - RECVFROM\n");
exit(1);
}

Can you help me?

thanks

Using #define with a dll

Waldermort18-Aug-06 11:32

Waldermort

18-Aug-06 11:32

I have a multithreaded dll which reads and writes to files. For debugging purposes I would like to switch between multithreaded and singlethreaded from my main app. So I placed the following in the dll code

#ifdef _DLLNOUSETHREAD
    LoadMonthThread();
#else
    _handle = (HANDLE)_beginthreadex(NULL,0,LoadMonth,this,0,&_threadID);
    if (!_handle)
        ShowError();
#endif

I was hoping to simple be able to define _DLLNOUSETHREAD in the main exe to be able to switch, but it isn't working like that. The dll always fires a thread. What did I do wrong here?

Re: Using #define with a dll

C^hris L^osinger18-Aug-06 11:37

C^hris L^osinger

18-Aug-06 11:37

are you rebuilding the DLL when you change the #define ?

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