C / C++ / MFC

Re: bizarre problem with files [modified]

22-Jun-08 17:25

hi
i have aquestion i really need an answer for it because it frustrated me...
look at these two functions:

void CSecondDlg::OnButton1() 
{
	//**BROWSE DIALOG 1**//
	   FILE *fp;
	   FILE *file1 = fopen("file1.txt","w");   //Create txt file for saving editbox content
       int nFileLong;
	   //***********************************************//
       char strFilter[] = { "CPP Files (*.cpp)|*.cpp|All Files (*.*)|*.*||" };
	   CFileDialog m_ldFile(TRUE, ".cpp", NULL, 0, strFilter);
       if (m_ldFile.DoModal() == IDOK)        //Start File dlg box
	   {
       m_sFileName=m_ldFile.GetPathName();    //Get file name
       fp=fopen(m_sFileName,"rb");            //Open file for reading
       fseek(fp,0,SEEK_END);                  //Go to file end 
       nFileLong=ftell(fp);                   //Get length
       char* sText = new char[nFileLong+1];   //reserve string space
       fseek(fp,0,SEEK_SET);                  //Go to file start 
       int i=fread(sText,1,nFileLong,fp);     //Read the characters
       sText[i]=0;                            //Set string terminating null
       m_EDIT1=sText;                         //Put text in Edit box's variable
	   fprintf(file1,"%s\n",m_EDIT1);         //print the content of the editbox into the file 
       fclose(file1);                         //Close file2
	   fclose(fp);                            //Close file 
       UpdateData(FALSE);                     //Force data to go to Edit control
	   }
}

AND

void CSecondDlg::OnButton2() 
{
	//**BROWSE DIALOG 2**//
	   FILE *fp;
	   FILE *file2 = fopen("file2.txt","w");   //Create txt file for saving editbox content
       int nFileLong;
	   //***************************************************//
       char strFilter[] = { "CPP Files (*.cpp)|*.cpp|All Files (*.*)|*.*||" };
       CFileDialog m_ldFile(TRUE, ".cpp", NULL, 0, strFilter);
       if (m_ldFile.DoModal() == IDOK)        //Start File dlg box
	   {
       m_sFileName=m_ldFile.GetPathName();    //Get file name
       fp=fopen(m_sFileName,"rb");            //Open file for reading
       fseek(fp,0,SEEK_END);                  //Go to file end 
       nFileLong=ftell(fp);                   //Get length
       char* sText = new char[nFileLong+1];   //reserve string space
       fseek(fp,0,SEEK_SET);                  //Go to file start 
       int i=fread(sText,1,nFileLong,fp);     //Read the characters
       sText[i]=0;                            //Set string terminating null
       m_EDIT2=sText;                         //Put text in Edit box's variable
	   fprintf(file2,"%s\n",m_EDIT2);         //print the content of the editbox into the file 
       fclose(fp);                            //Close file
	   fclose(file2);                         //Close file2
       UpdateData(FALSE);                     //Force data to go to Edit control
   }
}

as u can see the two functions do the same thing :
open afile into an edit box ....then save the content of the edit box in another file (.txt)
what is bizzare??
well if i open browse1 and browse2 button ...i would find that the first file is created and the second not...(because i hit the button browse1 first).
if i try another time but with hitting browse2 first the opposite thing happend (the second file is changed but not the first )
what is wrong ????
i reaaaly dont know what to do ??
please help me with this
my project stopes on this....
thank u all

Saurabh.Garg22-Jun-08 17:58

22-Jun-08 17:58

I can't seem to find the difference between two functions. Can you step through your program and see what exactly is going on?

-Saurabh

modified on Monday, June 23, 2008 2:07 AM

lahom23-Jun-08 6:08

23-Jun-08 6:08

thanks for ur reply
but my application is simple ...two edit controls each with its "browse" button.
first load afile to edit .....then store the content of the edit to ".txt" file...
its that simple....
if u try it for the first time ...it works for both ...
but in second and third and .....etc times....the odd problem occures
??????????
what is it that i did wrong
please would u try it urself and help me understand and solve the problem
my project stop on this Cry | :((

thank u

Saurabh.Garg23-Jun-08 14:39

23-Jun-08 14:39

It doesn't matter that application is simple or complex. Point is you have a bug in your application that means there is a problem some where. So as I suggested why don't you try to step through your program and check whats going on. Another idea is just create a new application and copy this code over because the code you provided works fine for me.

-Saurabh

CPallini23-Jun-08 0:24

23-Jun-08 0:24

Well your code (though a bit weird: duplication) works on my system.
BTW why don't you delete the allocated memory?
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

lahom23-Jun-08 6:10

23-Jun-08 6:10

how????
did u tried it multiple times...
and in both way worked???
please i really need to know whats wrong...

CPallini23-Jun-08 6:42

23-Jun-08 6:42

Yes it actually works.
I've made three tests:
(1) Button1 followed by Button2 (loaded two different files)
(2) Button2 followed by Button1 (loaded two different files)
(3) Button1 followed by Button2 (loaded the same file)
All of them were OK.
Smile | :)

lahom25-Jun-08 6:55

25-Jun-08 6:55

ok...
what version of vc r u using>>>>>iam using 6
someone else tried it also and it didnot work out

CPallini25-Jun-08 11:07

25-Jun-08 11:07

Are you kidding?

lahom25-Jun-08 12:25

25-Jun-08 12:25

no iam not .... iam serious
whats wrong???? Cry | :((

CPallini25-Jun-08 21:00

25-Jun-08 21:00

Well, I'll try also on VS6. Maybe this evening (here I've only VS2005).
Smile | :)

Re: bizarre problem with files [modified]

Kwanalouie23-Jun-08 1:47

Kwanalouie

23-Jun-08 1:47

I'm not real familiar with code on the heap, but the statement

char* sText = new char[nFileLong+1]; //reserve string space

is created with "new". Doesn't that require a "delete" or equivalent (I don't know the syntax) to de-allocate that space? If you don't then that space can't get re-allocated since the pointer is lost when you exit the procedure. Don't know what kinds of problems could occur as a result.

Kwanalouie24-Jun-08 0:24

Kwanalouie

24-Jun-08 0:24

One problem your code has is in the method you are opening the files with fopen. There are two modes for reading and writing to files - binary mode and text mode. Some character conversions change in those two modes. When you open file1 and file2 you do not specify what mode to use, so the default mode is used. When you open m_sFileName you tell it to open it to read in binary mode instead of text mode.

Try changing the "w" to "wt" in this statement of yours
FILE *file1 = fopen("file1.txt","w");

And more importantly change the "rb" to "rt" since you are trying to read characters in the following statement in your code
fp=fopen(m_sFileName,"rb"); //Open file for reading

The ftell and fseek functions may not give the correct lengths if the file is opened in text mode, however. So you should simplify things and use the fgets() function to get the string you want.

Since you are working with text files they should be opened with the text attribute.

modified on Tuesday, June 24, 2008 6:30 AM

there is a questioin about function pointer and template

CresShadow22-Jun-08 16:18

CresShadow

22-Jun-08 16:18

i created following code.

template <typename t>
class c{
public:
int f1(){ fp=f1; return 1;};
char* f2(){ fp=f2; return "hi";};
t recentFunction(){ return fp(); }
private
t (*fp)();
}

is it validity?
i wanna get a code for recentFunction
i do not know how to implement compounding funtion point and template
pleae help me Smile | :)

Re: there is a questioin about function pointer and template

Saurabh.Garg22-Jun-08 17:31

Visual Studio: Where do I put my stuff?

22-Jun-08 17:31

Try something like this.

template <typename t> class c
{
public:
	
	typedef t (c::*FuncPtr)();
	
	int f1()
	{
		mFp=&c::f1;
		return 1;
	}
	
	char* f2()
	{
		mFp=&c::f2;
		return "hi";
	}
	
	t recentFunction()
	{
		return (this->*mFp)();
	}
	
private:
	
	FuncPtr mFp;
};

Test it using this.

c<int> c1;
c<char*> c2;


c1.f1();
// c1.f2(); // Invalid.
int x = c1.recentFunction();


//c2.f1(); // Invalid.
c2.f2();
char* ret = c2.recentFunction();

If you want to read more about member function pointer search for delegates. There are numerous articles on this topic on codeproject. One of them is Member Function Pointers and the Fastest Possible C++ Delegates[^].

-Saurabh

bkelly1322-Jun-08 16:06

bkelly13

22-Jun-08 16:06

This question is difficult to ask. The concept is simple, but the details of explaining it just go on and on.

Using Visual Studio 2008, I have created an application with MFC. In this application there is to be a linked list of instantiated objects. This list is to live the lifetime of the program and be publically accessible.

Not being familiar at all with the windows concept, where do I instantiate/create this object? There is no place within the code that VS created that I recognize as being something that can hold a permanent variable.

If the question is clear at this point, you might want to stop reading now. I am confused so the remainder of this post may be even more confusing.

The base class that VS created is listed below. Where should I insert something like:

CMyClass myinstance = new( CMyClass );

Or maybe:

CMyClass myinstance;

I want that because in another class I wish to write:

CMyClass::myinstance.LinkNewItem( new_item );

Hopefully this will cause a new item to be linked in to the linked list and other code can traverse the list to work with the data.

It none of this is appropriate, please advise as to what is appropriate.

Here is the cpp file that VS created. Where does my code belong?:

// test1.cpp : Defines the class behaviors for the application.
//

#include "stdafx.h"
#include "test1.h"
#include "test1Dlg.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

// Ctest1App

BEGIN_MESSAGE_MAP(Ctest1App, CWinApp)
ON_COMMAND(ID_HELP, &CWinApp::OnHelp)
END_MESSAGE_MAP()

// Ctest1App construction

Ctest1App::Ctest1App()
{
// TODO: add construction code here,
// Place all significant initialization in InitInstance
}

// The one and only Ctest1App object

Ctest1App theApp;

// Ctest1App initialization

BOOL Ctest1App::InitInstance()
{
// InitCommonControlsEx() is required on Windows XP if an application
// manifest specifies use of ComCtl32.dll version 6 or later to enable
// visual styles. Otherwise, any window creation will fail.
INITCOMMONCONTROLSEX InitCtrls;
InitCtrls.dwSize = sizeof(InitCtrls);
// Set this to include all the common control classes you want to use
// in your application.
InitCtrls.dwICC = ICC_WIN95_CLASSES;
InitCommonControlsEx(&InitCtrls);

CWinApp::InitInstance();

AfxEnableControlContainer();

// Standard initialization
// If you are not using these features and wish to reduce the size
// of your final executable, you should remove from the following
// the specific initialization routines you do not need
// Change the registry key under which our settings are stored
// TODO: You should modify this string to be something appropriate
// such as the name of your company or organization
SetRegistryKey(_T("Local AppWizard-Generated Applications"));

Ctest1Dlg dlg;
m_pMainWnd = &dlg;
INT_PTR nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK
}
else if (nResponse == IDCANCEL)
{
// TODO: Place code here to handle when the dialog is
// dismissed with Cancel
}

// Since the dialog has been closed, return FALSE so that we exit the
// application, rather than start the application's message pump.
return FALSE;
}

Thanks for your time

Re: Visual Studio: Where do I put my stuff?

Saurabh.Garg22-Jun-08 17:39