Re: Function out of scope - C / C++ / MFC Discussion Boards

hrishiS8-Sep-09 2:09

8-Sep-09 2:09

thanks for all the points... I can understand How much I have to learn more in deep ...And sorry to the real sender of the question... pls listen/take advice from the the seniors...I am too a learner

-----------------------------
I am a beginner

Re: Function out of scope [modified]

Cedric Moonen8-Sep-09 1:17

Cedric Moonen

8-Sep-09 1:17

There's no problem with your code. The problem appears when you return something like this:

char* ToStr()
{
  return "test";
}

In which case you return the address of a temporary variable. If you return an object, the compiler will make a copy of it and assign it to val correctly.

EDIT: changed the return type to char* instead of CString.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

modified on Tuesday, September 8, 2009 9:54 AM

Re: Function out of scope

Stuart Dootson8-Sep-09 3:52

Stuart Dootson

8-Sep-09 3:52

You sure about that Cedric?

I think you'll find that "test" is used to construct a CString object that's returned by copy...that's what happened when I compiled and debugged it, anyway Smile | :)

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: Function out of scope

Cedric Moonen8-Sep-09 3:55

Cedric Moonen

8-Sep-09 3:55

Ooops, sorry,I forgot to change the return type to char* Blush | :O

If the return type is CString, then I agree with you, there's no problem neither.

Thanks for pointing it out.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

Re: Function out of scope

N a v a n e e t h8-Sep-09 4:22

N a v a n e e t h

8-Sep-09 4:22

~~I don't find any issues with your code. You are returning by value and not returning any reference to the temporary. So I guess your code is perfectly valid.~~

Cedric Moonen wrote:
If you return an object, the compiler will make a copy of it and assign it to val correctly.

Even if you return by value, with return value optimization, a copy won't be made.

Please correct me if I am wrong here.

[edit]Saw your post updated[/edit]

Smile | :)

Navaneeth

How to use google | Ask smart questions

Re: Function out of scope

Joe Woodbury8-Sep-09 5:29

Joe Woodbury

8-Sep-09 5:29

Your example isn't be a problem since "test" is in the data segment and isn't going to change location. I would recommend returning a const char *, but that code is perfectly fine. What isn't fine is the following:

char* ToStr()
{
  char buffer[5];
  lstrcpy(buffer, "test");
  return buffer;
}

Re: Function out of scope

Stuart Dootson8-Sep-09 3:55

Stuart Dootson

8-Sep-09 3:55

If CString is the standard ATL/MFC string class, then there is nothing wrong with the code you've posted - ret will effectively be copied into val when the return statement is executed. Part of the implied contract of ToStr is that callers will pass the address of a CString object into which the return value can be copied.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: Function out of scope

Richard MacCutchan8-Sep-09 5:10

Richard MacCutchan

8-Sep-09 5:10

Stuart Dootson wrote:
Part of the implied contract of ToStr is that callers will pass the address of a CString object

Not exactly - the original post shows:

CString ToStr()
{
    CString ret = "test";
    return ret;
}

void fun()
{
    CString val = ToStr(); // it returns nothing (bad pointer)
}

The contract here is that ToStr() will return a CString object, which the caller may store or destroy as he/she wishes. The code as written always returns a valid CString object so I don't see how it can fail. However function fun() does nothing with its CString val so that may be where the original problem occurred.

Re: Function out of scope

Stuart Dootson8-Sep-09 5:43

Stuart Dootson

8-Sep-09 5:43

Note the use of the word 'implied' Smile | :)

An object (of struct/class type) gets returned from a function in C/C++ by the caller making space for it and the return statement in the function copying the actual value returned (ret in this case) into this space, constructing a temporary, unnamed object. This temporary object is then used in the callers context (in this case, it gets assigned to val).

A compiler is permitted to optimise away this temporary object when suitable, by giving the function a reference to the final destination (in this case val) rather than the temporary object.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: Function out of scope

Richard MacCutchan8-Sep-09 11:44

Richard MacCutchan

8-Sep-09 11:44

Good point, I had not considered the full implications of optimisation.

Re: Function out of scope

Moak9-Sep-09 1:21

Moak

9-Sep-09 1:21

<Slashdot style comment> Vote parent up! Smile | :)

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How to change the font of a button ?

ilgale8-Sep-09 0:52

ilgale

8-Sep-09 0:52

I've to develop an user interface where buttons has
different font types and dimensions (different from
the default window type). I've seen that the CButtonST
class doesn't do that... and the CButton::SetFont
method called with the output of the CFont::CreatePointFont
doesn't work properly.
Does someone have some advices ?

Thanks a lot !

Re: How to change the font of a button ?

Michael Schubert8-Sep-09 0:58

Michael Schubert

8-Sep-09 0:58

Something like this should work:

CFont f1;
LOGFONT lf1;
::ZeroMemory(&lf1, sizeof(lf1));
lf1.lfHeight = 14;
lf1.lfCharSet = ANSI_CHARSET;
lf1.lfWeight = FW_BOLD;
::lstrcpy(lf1.lfFaceName, "Arial");
f1.CreateFontIndirect(&lf1);
GetDlgItem(IDC_BUTTON)->SetFont(&f1);
f1.Detach();

Change lfHeight, lfCharSet and lfWeight to your liking.

EM_SETTABSTOPS and tab width in pixels?

Moak8-Sep-09 0:42

Moak

8-Sep-09 0:42

Hi,

I would like to change the appearance of tabs in a multiline edit control, all tabs should have the same width of 8 pixels. MSDN[^] talks about dialog units, where I would like to specify pixels. The following line sets the distance to "something" depending on the font size of the edit control:

int nTabWidth = 8; m_edit.SetTabStops(nTabWidth); //or optionally....
::SendMessage(m_edit.m_hWnd, EM_SETTABSTOPS, 1, (LPARAM)(LPINT)&nTabWidth);

How to calculate the correct value? Thanks for any help.

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Re: EM_SETTABSTOPS and tab width in pixels?

Moak8-Sep-09 4:46

Moak

8-Sep-09 4:46

Moak wrote:
How to calculate the correct value?

Not sure about this, but it seems to work...

int nTabWidthInDialogUnits = ::MulDiv(nTabWidth, 4, LOWORD(::GetDialogBaseUnits()));

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Re: EM_SETTABSTOPS and tab width in pixels?

ItaniumX29-Jan-10 7:34

ItaniumX

29-Jan-10 7:34

EM_SETTABSTOPS message gets tabswidth in dialog units, which equal to: 1 character = 4 dialog units width / 8 dialog units height (independent of the selected font).

As you can see in Remarks section from http://msdn.microsoft.com/en-us/library/bb761663%28VS.85%29.aspx[^], to convert measurements from dialog template units to screen units (pixels), use the MapDialogRect function.

Hope this helps.

Non technical C++ question

Ahmed Charfeddine8-Sep-09 0:34

Ahmed Charfeddine

8-Sep-09 0:34

There are many products publicied and which their authors proudly specify the langage/technology in which they are written.
In order to avoid to cite particular site : I can read things like :
"Written in .Net"
"Pure Managed"
"Full Web"

There are many labels and they are as if to serv the good image of the application.

Now, can I do that for a C++ program ?
Unmanaged high performance C++ Laugh | :laugh:

Do you have other suggestions ?
What about the icon, what can I put ( C++)

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www.potatosoftware.com

Re: Non technical C++ question

CPallini8-Sep-09 0:49

CPallini

8-Sep-09 0:49

what about

Pure 100% unmanaged high speed Potato++ software

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]

Re: Non technical C++ question

Moak8-Sep-09 0:52

Moak

8-Sep-09 0:52

Potato software wrote:
Now, can I do that for a C++ program ?
Unmanaged high performance C++ Laugh

Advertise as following...
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Optionally with:
Follow us on Youtube/Twitter/Facebook/Lolcats. Smile | :)

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Re: Non technical C++ question

Ahmed Charfeddine8-Sep-09 0:54

Ahmed Charfeddine

8-Sep-09 0:54

Easy Profiler : a compile-time profiler for C++
www.potatosoftware.com

Re: Non technical C++ question

Michael Schubert8-Sep-09 1:12

Michael Schubert

8-Sep-09 1:12

Potato Software
Performance-wise only one step short of hand-typed machine code

MySQL Can't create an instance of Command

MsmVc8-Sep-09 0:19

MsmVc

8-Sep-09 0:19

Hi
I am useing ODBC 5.1 Driver for connect to MySQL.It's working fine for XP OS.I am getting error on Window Server.on server OS i an able to connect but after connection i am getting error.

Can't create an instance of Command

code

	CString por="Driver={MySQL ODBC 5.1 Driver};";
	CString Database="Database="";";
	CString User="User=";
	CString Userp=root;
	CString password=";Password=";
	CString Passwords=root;
	CString option=";Option=3;";
	CString final=por;
	final +=Database;
	final +=User;
	final +=Userp;
	final +=password;
	final +=Passwords;
	final +=option;
	
	CoInitialize (NULL);
		
	_bstr_t strCon(final);

	try	
	{
		HRESULT hr = m_pConn.CreateInstance (__uuidof (Connection));

		if (FAILED (hr))
		{
			
		}
		
		if (FAILED (m_pConn->Open (strCon,bstrString,bstrString1,0)))
		{
			AfxMessageBox ("Can't open datasource");
		}
		GetDlgItemText(IDC_EDIT4,m_cbrow);
		GetDlgItemText(IDC_EDIT1,m_host);
		if(m_host=="localhost")
		{
		}
		else
		{
			MessageBox("There is an error to connect with MySQL. Please check your input parameters or server configuration.","Message",MB_ICONEXCLAMATION);
			return;
		}
		
			AfxMessageBox ("Connection successfully");	
		
			_CommandPtr pCommand;
			hr = pCommand.CreateInstance (__uuidof (Command));
<code>"Erro showing here"</code>
		if (FAILED (hr))
		{
			AfxMessageBox ("Can't create an instance of Command");
			return;
		}
			::_RecordsetPtr pRecordset;
			
			pCommand->ActiveConnection = m_pConn;

Plz help me.

Re: MySQL Can't create an instance of Command

MsmVc8-Sep-09 2:08

MsmVc

8-Sep-09 2:08

Plz help me.

Re: MySQL Can't create an instance of Command

MsmVc8-Sep-09 18:31

MsmVc

8-Sep-09 18:31

I have no idea.Plz help me

CString count

rdop7-Sep-09 23:19

rdop

7-Sep-09 23:19

Hi All

How can i ReversFind and count number of words?I have CString name="agsdfgggggg" how can count and cut these part "gggggg" from name.
I mean i want to show this CString name="agsdfgggggg" to CString name="agsdf".
Can any one help me.

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