C / C++ / MFC Discussion Boards

D.Manivelan15-May-12 2:29

15-May-12 2:29

Hi,
I want to read line from a file and after reading that line i have to delete that line.I think deleting a line in file is difficult.So i thought to replace the line with null string.
For that i coded below..first i test with text "TEST" for updating.But i could not get that.

if ( (fpExe=fopen((LPCTSTR)sExePath, "r+"))!=NULL)
	{							
		while(fgets(List,80,fpExe)!=NULL)
		{
		sReadLine = List;	
		off1 = ftell(fpExe);
		result = fseek( fpExe, off1,SEEK_SET);
		fprintf( fpExe, "%s", "TEST" );

					}
		fclose(fpExe);	
		return false;
	}
	else
	{
		return false;
	}

Example:
INSTRUCTOR1
INSTRUCTOR2
this should become
TEST
TEST

But actually what comes as
INSTRUCTOR1
TESTRUCTOR1

So how can i replace string with null or another string.

Re: Read and Write a same file in FILE

_Flaviu15-May-12 2:53

_Flaviu

15-May-12 2:53

As far as you open the file in read mode, you can not write anything in that file ...

Re: Read and Write a same file in FILE

CPallini15-May-12 2:57

CPallini

15-May-12 2:57

What are you trying to do, exactly?
If you need to manipulate the content of a file the usual way is:

Read the file content into memory.
modify it
Write the modified content to another file (say "output").
delete the original file and rename the "output" file you produced with the original filename.

Veni, vidi, vici.

Re: Read and Write a same file in FILE

Richard MacCutchan15-May-12 2:59

Richard MacCutchan

15-May-12 2:59

You cannot do it that way; a file is merely a stream of bytes and overwriting something with a shorter value will leave garbage in the stream. You need to follow something similar to my response here[^], but using text instead of PDF files and changing lines rather than pages. If you want to delete a line then merely read it and ignore it.

Programming is work, it isn't finger painting. Luc Pattyn

Re: Read and Write a same file in FILE

Aescleal15-May-12 4:38

Aescleal

15-May-12 4:38

Just to amplify CPalini's answer - if you're doing line oriented I/O then open the file for reading, open another for writing then process each line from the input file putting the results in the output file.

Another thing you could try is have fixed length records in the file. Then to read a record all you have to do is fseek to (record_size * index_of_record). To replace it you just write to the same place and to erase it you just mark the entry as empty somehow. This means you only need a single file open but makes the logic a bit more complicated.

Cheers,

Ash

In C, how to read data from a file

Baddy_Bad_Boy15-May-12 1:25

Baddy_Bad_Boy

15-May-12 1:25

HI guys,
How to read data from a file and save that data

Re: In C, how to read data from a file

Richard MacCutchan15-May-12 1:30

Richard MacCutchan

15-May-12 1:30

See here[^], paying particular attention to CreateFile(), ReadFile() and WriteFile().

[edit]
On second thoughts you may be better to start here[^] for pure C.
[/edit]

Programming is work, it isn't finger painting. Luc Pattyn

Multiprocessor sort and search in C?

Simon Langdon14-May-12 23:28

Simon Langdon

14-May-12 23:28

Is there a multiprocessor implementation of qsort and bsearch out there? My app. is mostly in C but some bits have got C++ and STL depending on what libraries are needed. We compile with VS2008 so openMP is available.

Re: Multiprocessor sort and search in C?

David Crow15-May-12 3:47

David Crow

15-May-12 3:47

An article I read recently on sorting in parallel: http://www.drdobbs.com/blogs/parallel/232600358?pgno=1[^]

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous

Re: Multiprocessor sort and search in C?

TomasRiker217-May-12 8:11

TomasRiker2

17-May-12 8:11

Look at this one as well:
http://berenger.eu/blog/2011/10/06/c-openmp-a-shared-memory-quick-sort-with-openmp-tasks-example-source-code/[^]

Visit my project: Derivative Calculator

MFC help : code error 0000007B

jawadali47714-May-12 21:57

jawadali477

14-May-12 21:57

hi,
i'm developing GUI using MFC in vs2008. i have developed code and it builds fine but when i debug my code, it gives system error 0000007B. part of the code that gives this error is given below + variable initialization.

int COMportNum= 3;
portstream_fd COMstream;
portstream_fd pstream;
char COMportPrefix[10] = "COM";
char COMportName[256];
 
sprintf(COMportName, "%s%d", COMportPrefix, COMportNum); // initialize serial port COM3
 
strng = CString(COMportName);
strng.Format(_T("%0.9s"), strng);
SetDlgItemText(IDC_STAT, strng);
 
set_baud_rate(BaudRate);
COMstream = open_host_port(COMportName); //opens serial port COM3
 
if ( COMstream == PORT_NOT_OPENED ) //conditional check if COM3 is opened
{
stw.Format(_T("%08X"), GetLastError()); //generates error if any
SetDlgItemText(IDC_PTUPORT, stw);
}
else 
SetDlgItemText(IDC_PTUPORT, (LPCTSTR) L"Ok");

can anyone please help me with this error.

Regards 
Jawad

Re: MFC help : code error 0000007B

enhzflep14-May-12 22:24

enhzflep

14-May-12 22:24

Hi there,

I don't want to seem pedantic, though I will point out that this is not actually system error 0x0000007B, but rather the error-code of the last system function that failed. A system error is one generally regarded as having been generated by Windows itself (rather than just a 'helper' function)

Something that you may choose to do which certainly clarifies the error is to display a description of the error.

Have a look over here, for a method by which the code 0x7B may be turned into a text message.

Re: MFC help : code error 0000007B

CPallini14-May-12 22:27

CPallini

14-May-12 22:27

The error message is (you can check it in WinError.h)

//  The filename, directory name, or volume label syntax is incorrect.

What library are you using?

Veni, vidi, vici.

Re: MFC help : code error 0000007B

jawadali47714-May-12 23:42

jawadali477

14-May-12 23:42

basically i have the console program running fine (means having source file and header files). than i wanted to build GUI for this using MFC in vs2008. now i don't understand how to open serial port in MFC. code below shows how to open serial port in console programming using cmd prompt.

COMportName[0] = ' ';
     while (COMportName[0] == ' ') {
         printf("\nEnter the %s port number the PTU is attached to: ", COMportPrefix);
         scanf("%d", &COMportNum);
         printf("You selected %s%d. Is this OK? (enter 'y' or 'n'): ", COMportPrefix, COMportNum);
         tmpChar = 'f';
         while ( (tmpChar != 'y') && (tmpChar != 'n') )
               tmpChar = ((char) tolower(getchar()));
         if ( tmpChar == 'y' )
            sprintf(COMportName, "%s%d", COMportPrefix, COMportNum);
     }
     tmpChar = 'f';
     while (tmpChar != 'y') {
         printf("\nEnter the baud rate the ptu is communicate at (default: 9600): ");
         scanf("%d", &BaudRate);
         printf("You selected %d. Is this OK? (enter 'y' or 'n'): ", BaudRate);
         tmpChar = 'f';
         while ( (tmpChar != 'y') && (tmpChar != 'n') )
               tmpChar = ((char) tolower(getchar()));
     }


     /* initialize the serial port */
     set_baud_rate(BaudRate);
     COMstream = open_host_port(COMportName);

     if ( COMstream == PORT_NOT_OPENED )
         { printf("\nSerial Port setup error.\n");
           goto abnormal_exit;  }
     printf("\nSerial port %s initialized\n", COMportName);

Re: MFC help : code error 0000007B

CPallini14-May-12 23:52

CPallini

14-May-12 23:52

jawadali477 wrote:
COMstream = open_host_port(COMportName);

I would use the debugger to watch COMportName content in both console and MFC applications.

Veni, vidi, vici.

Re: MFC help : code error 0000007B

jawadali47716-May-12 19:14

jawadali477

16-May-12 19:14

console program is running fine. problem is in MFC program. can you tell how to implement the console program, as mentioned, in MFC??

Re: MFC help : code error 0000007B

TinyDevices15-May-12 3:32

TinyDevices

15-May-12 3:32

What a mix up of different naming conventions!

Re: MFC help : code error 0000007B

Andy41114-May-12 22:49

Andy411

14-May-12 22:49

As CPallini pointed out

CPallini wrote:
The error message is (you can check it in WinError.h)
//  The filename, directory name, or volume label syntax is incorrect.

Are you sure COM3 exists on your machine?
Did you try the format \\.\COM3 instead?

What happens in set_baud_rate() and in open_host_port()? You have to open the COM-Port before changing the baudrate

Cou can find some more hints on serial communication here:
Communications Resources[^]

[Edit]corrected spelling of memeber name Blush | :O

[/Edit]

modified 15-May-12 5:16am.

Re: MFC help : code error 0000007B

CPallini14-May-12 23:09

CPallini

14-May-12 23:09

Andy411 wrote:
JPalini

Veni, vidi, vici.

Re: MFC help : code error 0000007B

Andy41114-May-12 23:18

Andy411

14-May-12 23:18

Oooouuuuuuch
Sorry, I just corrected it. Sometimes I don't have any control on what my fingers are doing with the keyboard Rose | [Rose]

Re: MFC help : code error 0000007B

jawadali47714-May-12 23:46

jawadali477

14-May-12 23:46

yes COM3 is available and i have tried \\.COM3 and \\\\.\\COM3 both. basically i'm developing GUI via MFC in vs2008 for my console program. part of the code for opening serial port in console program is given below. i can't understand how to do it in MFC.

COMportName[0] = ' ';
     while (COMportName[0] == ' ') {
         printf("\nEnter the %s port number the PTU is attached to: ", COMportPrefix);
         scanf("%d", &COMportNum);
         printf("You selected %s%d. Is this OK? (enter 'y' or 'n'): ", COMportPrefix, COMportNum);
         tmpChar = 'f';
         while ( (tmpChar != 'y') && (tmpChar != 'n') )
               tmpChar = ((char) tolower(getchar()));
         if ( tmpChar == 'y' )
            sprintf(COMportName, "%s%d", COMportPrefix, COMportNum);
     }
     tmpChar = 'f';
     while (tmpChar != 'y') {
         printf("\nEnter the baud rate the ptu is communicate at (default: 9600): ");
         scanf("%d", &BaudRate);
         printf("You selected %d. Is this OK? (enter 'y' or 'n'): ", BaudRate);
         tmpChar = 'f';
         while ( (tmpChar != 'y') && (tmpChar != 'n') )
               tmpChar = ((char) tolower(getchar()));
     }


     /* initialize the serial port */
     set_baud_rate(BaudRate);
     COMstream = open_host_port(COMportName);

     if ( COMstream == PORT_NOT_OPENED )
         { printf("\nSerial Port setup error.\n");
           goto abnormal_exit;  }
     printf("\nSerial port %s initialized\n", COMportName);

Re: MFC help : code error 0000007B

Andy41114-May-12 23:59

Andy411

14-May-12 23:59

Does the console programm run?
And what's the code inside open_host_port()?
Did you step through the code of open_host_port() in the debugger? Examine every return code of Win32 API-calls and check GetLastError().

What happens, if you just do a call to the CreateFile-function to open the COM-port, just like in this article

Creating a Serial communication on Win32[^]

I dont't think that this is an MFC problem,

Re: MFC help : code error 0000007B

David Crow15-May-12 3:52

David Crow

15-May-12 3:52

Andy411 wrote:
I dont't think that this is an MFC problem,

I agree.

Re: MFC help : code error 0000007B

David Crow15-May-12 3:58

David Crow

15-May-12 3:58

jawadali477 wrote:
char COMportPrefix[10] = "COM";
char COMportName[256];

sprintf(COMportName, "%s%d", COMportPrefix, COMportNum); // initialize serial port COM3

strng = CString(COMportName);
strng.Format(_T("%0.9s"), strng);
SetDlgItemText(IDC_STAT, strng);

I'm thinking you could eliminate some overhead here. Try:

strng.Format(_T("COM%d"), COMportNum);

Note that this likely has nothing to do with why open_host_port() is not opening the port.

Re: MFC help : code error 0000007B

soaringpilot15-May-12 10:44

soaringpilot

15-May-12 10:44

I do not recognize the open_host_port function, but it does not really matter. On some systems you need to add a ':' after COMx. Try sprintf(COMportName, "%s%d:", COMportPrefix, COMportNum); to get COM3:

Cheers,
Henryk

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