C / C++ / MFC

17-Jul-06 0:09

Hello everyone,

I have verified that the following approach works to set the size of a file (newly created file) to be 100 bytes, but I am not sure whether it is the correct/best way to have a maximum portability (I need to write code on both Windows and Linux).

Could anyone give me any comments?

<br />
#include "fcntl.h"<br />
#include "sys/types.h"<br />
#include "sys/stat.h"<br />
#include "io.h"<br />
#include "stdio.h"<br />
<br />
int main()<br />
{<br />
	FILE* file = fopen ("foo123", "w+");<br />
	<br />
	fseek (file, 99, SEEK_SET);<br />
<br />
	fprintf (file, "x");<br />
<br />
	fclose (file);<br />
<br />
	return 0;<br />
}<br />

thanks in advance,
George

-- modified at 6:11 Monday 17th July, 2006

David Crow17-Jul-06 2:44

17-Jul-06 2:44

It's probably a lot more portable than SetEndOfFile(). Wink | ;)

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

George_George17-Jul-06 3:05

17-Jul-06 3:05

Thank you DavidCrow!

What do you mean SetEndOfFile()? Is there a method called SetEndOfFile() in C?

regards,
George

David Crow17-Jul-06 3:49

17-Jul-06 3:49

George_George wrote:
Is there a method called SetEndOfFile() in C?

There's a function called SetEndOfFile().

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

George_George17-Jul-06 4:08

17-Jul-06 4:08

Thank you DavidCrow!

Why my method is better than SetEndOfFile()?

regards,
George

David Crow17-Jul-06 4:14

17-Jul-06 4:14

George_George wrote:
Why my method is better than SetEndOfFile()?

You wanted portability, didn't you?

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

George_George17-Jul-06 20:49

17-Jul-06 20:49

Thank you DavidCrow!

Yes, I mean why SetEndOfFile() has worse portability?

regards,
George

David Crow18-Jul-06 2:34

18-Jul-06 2:34

George_George wrote:
...why SetEndOfFile() has worse portability?

It's only for a Windows platform.

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

George_George18-Jul-06 22:26

18-Jul-06 22:26

Thank you DavidCrow!

regards,
George

earl17-Jul-06 4:57

earl

17-Jul-06 4:57

There's two ways to get portability; the first is to use a common API and test it enough to make sure it works the same way on both systems; the second is to do such:

int main(int argc, char** argv)
{
  #if defined(WINDOWS)
  //put windows code here

  #elif defined(LINUX)
  //code that does the same thing in linux
  #endif

  return 0;
}

The former tends to make for much more readable code... at least IMO.

earl

George_George17-Jul-06 20:51

17-Jul-06 20:51

Thank you earl!

Your sample is only the general principle to develop portable code. In my case, to set the length of a file, is my method showed above has good portability? Do you have any better ideas or any comments?

regards,
George

Re: is this the correct/best way to set file size? [modified]

earl18-Jul-06 6:40

earl

18-Jul-06 6:40

Why do you need the file to be 100b?

I imagine your example should work, unless there are examples of sparse filesystems in use? I doubt it, but I don't keep up with the various file systems in use under linux.

Alternatively, you could just fwrite 100b of zeroes...

unsigned char buff[100];
memset(buff, 0x0, 100 * sizeof(unsigned char));

fwrite(buff, sizeof(unsigned char), 100, fp);

earl

George_George18-Jul-06 22:28

18-Jul-06 22:28

Thank you earl!

Your method is using more memory compared with my method -- 100 more bytes for the local char array. Agree?

regards,
George

-- modified at 4:28 Wednesday 19th July, 2006

earl19-Jul-06 3:14

earl

19-Jul-06 3:14

Sure, but who cares? As written it'll be allocated on the stack and disappear after the function is finished. You also could call fwrite 100 times on a single byte, if you're working in a space where 100b matters.

earl

George_George19-Jul-06 20:34

19-Jul-06 20:34

Thank you earl!

regards,
George

Edit box

SandhyaSri17-Jul-06 0:08

SandhyaSri

17-Jul-06 0:08

Hi,

I have declared an integer type variable for an edit box.My requirement is I want the edit box to be left blank i.e there should be no "0" when it is displayed.How can this be done?

Thanks in advance

Sandhya

Parthi_Appu17-Jul-06 0:23

Parthi_Appu

17-Jul-06 0:23

Before showing the Edit Control set its window text to null.
that is, if you are using dialog based application then in OnInitDialog() use the below statement;

GetDlgItem(EditCtrlID)->SetWindowText("");
or
if you have a control variable say m_editctrl then
m_editctrl.SetWindowText("");

Do your Duty and Don't expect the Result

_AnsHUMAN_ 17-Jul-06 0:27

_AnsHUMAN_

17-Jul-06 0:27

SetDlgItemText (IDC_MYEDIT,"");

Somethings seem HARD to do, until we know how to do them.
Wink | ;-)

_AnShUmAn_

Parthi_Appu17-Jul-06 0:36

Parthi_Appu

17-Jul-06 0:36

i forget the SetDlgItemText(..).
This will be more appropriate than SetWindowText():->

Do your Duty and Don't expect the Result

Re: CString to char [modified]

Smith#17-Jul-06 1:30

Smith#

17-Jul-06 1:30

SetWindowText() is still good . dont worry .

Wink | ;)

CString to char

vc++_fragrance16-Jul-06 23:41

vc++_fragrance

16-Jul-06 23:41

Hi,
Please can u say How can we convert CString variable to char data type.
Thanks in advance,

tejaswini

Re: CString to char

Rajesh R Subramanian16-Jul-06 23:47

Rajesh R Subramanian

16-Jul-06 23:47

<br />
char myCharVar[20];<br />
CString myStrVar;<br />
<br />
myStrVar = "This will be copied";<br />
myCharVar = myStrVar.GetBuffer(myStrVar.GetLength());<br />

You have an apple and me too. We exchange those and We have an apple each.
You have an idea and me too. We exchange those and We have two ideas each.

Parthi_Appu16-Jul-06 23:49

Parthi_Appu

16-Jul-06 23:49

if your application is not based on _UNICODE text then you can use CString.GetBuffer(). this will return the starting address of the string.
other wise store this CString value in stl string, and covert as mentioned

#include string //use angular brackets
using namespace std;

CString str;
string strTemp((LPCTSTR)str);
char szValue[..] = {0};
strcpy(szValue, strTemp.c_str());

Do your Duty and Don't expect the Result

-- modified at 5:55 Monday 17th July, 2006

Re: CString to char

David Crow17-Jul-06 2:49