C / C++ / MFC Discussion Boards

sakthimuhuu22-Jun-14 18:54

22-Jun-14 18:54

I have my program like this

int main()
{
char *p = "Test"
p++;
p++;
printf("%s", p[-1]);
return 0;
}

what will be printed by printf statment

Thanks,
Sakthi

Re: can be p[-1] dereferenced?

«_Superman_»22-Jun-14 20:22

«_Superman_»

22-Jun-14 20:22

The statement is perfectly valid "in this case".
Using an index will simply add it to the address.
So p[-1] will internally become *(p-1).

~~In this case, since you're incrementing p twice, p[-1] should print e.~~

Correction - My earlier comment would be true if you change the statement to printf("%c", p[-1]);

«_Superman_»
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Microsoft MVP (Visual C++) (October 2009 - September 2013)

Polymorphism in C

modified 23-Jun-14 4:07am.

Re: can be p[-1] dereferenced?

Jochen Arndt22-Jun-14 21:00

Jochen Arndt

22-Jun-14 21:00

p[-1] returns the character at that position ('e' in your case). When passing this value as address of a string to printf, it will try to print the memory content at the address 0x65 as string.

Re: can be p[-1] dereferenced?

CPallini22-Jun-14 22:16

CPallini

22-Jun-14 22:16

While p[-1] is valid (why didn't you try to compile it?), you are using it the wrong way: a char pointer (char *) is expected by the format specifier "%s" while you are passing a char ( p[-1], is like *(p-1), that is a char). You should have written either:

printf("%s\n", &p[-1]);

producing output

est

printf("%c\n",p[-1]);

, producing output

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Re: can be p[-1] dereferenced?

sakthimuhuu24-Jun-14 2:11

sakthimuhuu

24-Jun-14 2:11

But, when i executed the program in Visual studio i got run time error

Thanks,
Sakthi

Re: can be p[-1] dereferenced?

CPallini24-Jun-14 2:21

CPallini

24-Jun-14 2:21

What program? What error?
(Please provide both).

THESE PEOPLE REALLY BOTHER ME!! How can they know what you should do without knowing what you want done?!?!
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Re: can be p[-1] dereferenced?

Satya Chamakuri12-Aug-14 21:38

Satya Chamakuri

12-Aug-14 21:38

Hi,

int main()
{
char *p = "Test";
p++;
p++;
printf("%s", p[-1]);
getchar();
return 0;
}

Suppose think the starting address of p will be 0x20000,
You are incrementing p two times, so before entering to the highlighted line in above code value of p is 0x20002 and the content in that location as starting address will be st.

Then p[-1] means *(p-1), means value at 0x20001 location. means 'e'.

In printf, %s is a format specifier wich will try to display the string at the memory location provided in variable list. Here the address provided in variable list is value of *(p-1), i.e, 'e' (internally this is 0x65). So %s dereferences the value at 0x65, so some garbage value it will print finally. otherwise will terminate the program as memory is un referenced.

Thanks

DirectShow not showing mp4 & WndProc Not working

AmbiguousName20-Jun-14 1:23

AmbiguousName

20-Jun-14 1:23

Hello. I am trying to play video file using DirectShow found on this MSDN reference. I am facing two problems.
1- local H264 video doesn't get rendered properly. A frame shows and them some blocks keep showing.
2- Can not get notifications on my dialog window using WndProc. Using this sample.

I am using following code for getting events.

C++

void CDShowPlayerSampleDlg::OnStartPlay()
{
	CPlayer::m_hWndPlayerDlg = this->m_hWnd; // MainDlg->m_hWnd
	BOOL bResult = m_objPlayer.StartPlay(); // CPlayer m_objPlayer;
}

LRESULT CDShowPlayerSampleDlg::WindowProc(UINT message, WPARAM wParam, LPARAM lParam)
{
  switch(wParam) // lParam or wParam ?????????
  {
    case WM_GRAPHNOTIFY:
  }
  /* rest of the code here*/
}

Now I am setting the event notifications on the IGraphBuilder like this (in CPlayer).

HRESULT hResult = m_pGraphBuilder->QueryInterface(IID_IMediaEventEx, (void**)&m_pEvent);
hResult = m_pEvent->SetNotifyWindow((OAHWND)m_hWndPlayerDlg, WM_GRAPHNOTIFY, 0);

1- So why can not I get notifications in CDShowPlayerSampleDlg::WindowProc?
2- And why is that Windows Media Video (.wmv) file plays correctly but H264 does not. What could I do for smooth H264 playback?
Thanks for any pointers.

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modified 20-Jun-14 8:18am.

Re: Can not Get Notification using WndProc

Richard MacCutchan20-Jun-14 1:30

Richard MacCutchan

20-Jun-14 1:30

C++

switch(wParam) // will never work, the wParam and lParam variables hold other data

// you need to check the message number like:
switch(message)

Re: Can not Get Notification using WndProc

AmbiguousName20-Jun-14 2:04

AmbiguousName

20-Jun-14 2:04

Yes. it solved my problem.
On a different note, as you can see in my code OnStartPlay(), I am storing my MainDlg's HWND in the CPlayer. What if I don't have a window and I still want to process these kind of messages from CPlayer? Thanks

This world is going to explode due to international politics, SOON.

Re: Can not Get Notification using WndProc

Richard MacCutchan20-Jun-14 2:11

Richard MacCutchan

20-Jun-14 2:11

You must have a Window, in order to receive the WM_ messages. However, you can create a Window but not make it visible if necessary.

swprintf_s with *wstring (Resolved)

bkelly1319-Jun-14 6:39

bkelly13

19-Jun-14 6:39

Windows XP, Visual Studio 2008, C++

XML

bool procedure( wstring *target )
{...
int wrote_count = swprintf_s(
    text_to_log,
    MAX_SIZE,
    L"Target is %ls",
    target );
... }

The debugger shows text "Messsage" in variable target but text_to_log does not have that text.
text_to_log is declared as WCHAR text_to_log[ MAX_SIZE ] where MAX_SIZE is 400.
I have tried creating a local varible of type wstring and the text will copy from target to that local string. Using that local string in the printf statement produces the same result.

What do I need to change to incorporate the text from target into the text of text_to_log?

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

modified 19-Jun-14 14:22pm.

Re: swprintf_s with *wstring

David Crow19-Jun-14 6:54

David Crow

19-Jun-14 6:54

What is the value of wrote_count? If -1, what is errno set to?

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Re: swprintf_s with *wstring

bkelly1319-Jun-14 7:11

bkelly13

19-Jun-14 7:11

wrote_count is 57, I simplified some when writing this post. That value matches what is in the string it writes to. The text from target is simply missing in action.

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

Re: swprintf_s with *wstring

David Crow19-Jun-14 9:53

David Crow

19-Jun-14 9:53

bkelly13 wrote:
The text from target is simply missing in action.

How are you verifying this?

Re: swprintf_s with *wstring

Graham Breach19-Jun-14 7:09

Graham Breach

19-Jun-14 7:09

Just a guess, but try using target->c_str() in the swprintf_s function call instead of just target.

I believe the printf functions expect C-style strings, not C++ string classes.

Re: swprintf_s with *wstring

bkelly1319-Jun-14 7:21

bkelly13

19-Jun-14 7:21

Just tried that: error 2228, left of .c_str() must have class/struct/union

Edit:

(*target).c_str()

You got me most of the way there, evidently there is a precedence problem. With the above the text shows up.

Thank you for your help.

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

modified 19-Jun-14 13:38pm.

Re: swprintf_s with *wstring

Richard MacCutchan19-Jun-14 23:28

Richard MacCutchan

19-Jun-14 23:28

Why not just:

C++

target->c_str()

Could not get the ConnectionString from Registry Key

Member 1089437819-Jun-14 0:04

Member 10894378

19-Jun-14 0:04

I have given the value for the connetionstring and TeamsConnectionString in registry settings but s still i am facing the following error.

can anyone please suggest me to resolve this error

Error details from event details:
---------------------------------

The following information was included with the event:

Could not get the ConnectionString from Registry Key =SOFTWARE\Kimberly-Clark\Knowledge Management; Value = TeamsConnectionString
Last error number: 0

Re: Could not get the ConnectionString from Registry Key

Richard MacCutchan19-Jun-14 0:35

Richard MacCutchan

19-Jun-14 0:35

You need to show the code you are using to get the key, and the exact error message or return code.

Re: Could not get the ConnectionString from Registry Key

Member 1089437819-Jun-14 22:42

Member 10894378

19-Jun-14 22:42

lfLog.DebugMsgStart("  Retrieving Connection String");

csKey = "SOFTWARE\\Kimberly-Clark\\Knowledge Management";
  if ( !rReg.GetSZValue(HKEY_LOCAL_MACHINE,csKey, csConnectionStringReference, csConnectionString))
{
      // could not get program name
      lfLog.DebugMsgEnd("FAILED");
      csMsg.Format("Could not get the ConnectionString from Registry Key = '%s', Value = '%s'", csKey, csConnectionStringReference);
      elLog.ErrorMsg(csMsg);
      lfLog.ErrorMsg(csMsg);

      // log the message code
      mclLog.ErrorMsg( 0, "ConnectionString");
      goto exit30;
}
  lfLog.DebugMsgEnd("SUCCESS");



and i am having the values in registry under the path mentioned in the code

Re: Could not get the ConnectionString from Registry Key

Richard MacCutchan19-Jun-14 23:26

Richard MacCutchan

19-Jun-14 23:26

Very interesting, but what is happening when you run this code?
What does rReg.GetSZValue return and where is the class definition for it?
What is contained in csConnectionStringReference and csConnectionString?
What system calls are being used and if they fail what is returned by GetLastError()?

Re: Could not get the ConnectionString from Registry Key

Member 1089437820-Jun-14 4:00

Member 10894378

20-Jun-14 4:00

code compilation is success an now i am trying to install and run the service in the production server .

rReg.GetSZValue success if it successfully fetch the value from regtry path or else failed ,now it is returning fail in log .
csConnectionStringReference contained the key name "TeamsConncetionstring" and this value is also ftched from the registry itself.
csConnectionString should be stored with the value of the key "TeamsConncetionstring".

GetLastError() returning 0 here .

And if any error even will log with the error details which i have reported earlier.

Re: Could not get the ConnectionString from Registry Key

Richard MacCutchan20-Jun-14 4:08

Richard MacCutchan

20-Jun-14 4:08

I'm sorry but that tells us nothing about what is happening. You need to use your debugger to step through the code and see the exact status values that you are receiving when you try to read this value from the registry. You still have not shown the code that does to do the actual call to get the value from the registry, only rReg.GetSZValue.

Re: Could not get the ConnectionString from Registry Key

David Crow20-Jun-14 4:43

David Crow

20-Jun-14 4:43

What type of object is rReg?

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