can i use mem_fun like this? - C / C++ / MFC Discussion Boards

Re: CString assignment crashes on Windows 7

Stephen Hewitt18-Dec-12 17:44

Stephen Hewitt

18-Dec-12 17:44

The fix is far from perfect, you shouldn't need to call reserve. If I were you I'd be looking for the real problem.

Steve

Segmentation Fault in GTK library files

SrivathsanRaghavan2-Dec-12 19:20

SrivathsanRaghavan

2-Dec-12 19:20

Hi, I am developing an application that toggles the screen in Debian 6 Platform.

In earlier days I done this with Debian 5, It works good. But if I use the same code in Debian 6, I face a segmentation fault in libgtk-x11-2.0.so.2000.0 and libgdk-x11-2.0.s0.2000.0. Since they are Library files I cant do anything with that. Is there any other possibility to prevent my application from facing Segmentation fault???

Expecting for a quick reply

Thanks & Regards
Srivathsan

Re: Segmentation Fault in GTK library files

Richard MacCutchan2-Dec-12 21:47

Richard MacCutchan

2-Dec-12 21:47

I don't think anyone is likely to be able to guess why your program fails. You need to do some diagnosis to find out where the segmentation fault occurs, and what the last call out from your code was.

One of these days I'm going to think of a really clever signature.

Re: Segmentation Fault in GTK library files

SrivathsanRaghavan2-Dec-12 22:11

SrivathsanRaghavan

2-Dec-12 22:11

This is the Snippet I got when tried to trace the Segmentation fault using GDB

#0 0xb7281601 in ?? () from /usr/lib/libgdk-x11-2.0.so.0
#1 0xb7282835 in ?? () from /usr/lib/libgdk-x11-2.0.so.0
#2 0xb7052381 in ?? () from /lib/libglib-2.0.so.0
#3 0xb7054305 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#4 0xb7057fe8 in ?? () from /lib/libglib-2.0.so.0
#5 0xb7058527 in g_main_loop_run () from /lib/libglib-2.0.so.0
#6 0xb7418b69 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#7 0x080e82a1 in main_callback (data=0x0) at src/dispimage.c:155
#8 0xb707e6cf in ?? () from /lib/libglib-2.0.so.0
#9 0xb77a7955 in init_rotgrids(rotgrids**, int, int, int, double, int, int, int, int) () from /lib/i686/cmov/libpthread.so.0
#10 0xb6f99e7e in clone () from /lib/i686/cmov/libc.so.6

Re: Segmentation Fault in GTK library files

Richard MacCutchan2-Dec-12 22:28

Richard MacCutchan

2-Dec-12 22:28

#7   0x080e82a1 in main_callback (data=0x0) at src/dispimage.c:155

I guess that's your first clue. But really, you have to do some analysis here; we cannot begin to guess what is going on in your code.

One of these days I'm going to think of a really clever signature.

Re: Segmentation Fault in GTK library files

SrivathsanRaghavan3-Dec-12 0:25

SrivathsanRaghavan

3-Dec-12 0:25

I tried out with GDB to detect the place where Segmentation fault Occurs. I cant able to retrieve any local Variable's Information at that place. Is there any good tool to trace Segmentation Fault?

Thanks & Regards
Srivathsan

Re: Segmentation Fault in GTK library files

Richard MacCutchan3-Dec-12 0:55

Richard MacCutchan

3-Dec-12 0:55

SrivathsanRaghavan wrote:
Is there any good tool to trace Segmentation Fault?

None that I am aware of. Unfortunately they are often difficult to catch without a good back stacktrace. The best you can do is add some extra trace/debug code into your program and see if you can collect some more information before the fault occurs.

One of these days I'm going to think of a really clever signature.

can i use mem_fun like this?

Falconapollo1-Dec-12 17:37

Falconapollo

1-Dec-12 17:37

I want to set the function pointer at runtime. But i'm stuck here. When i use global function or static class member function, everything is ok. but, when the function is ordinary class member functions. i always got compiler errors. Here is the code:

C++

class A   
{
    int val;
public:
    A() { val = 0; }
    A(int j) { val = j; }

    int aFun(int k) {val -= k; return val; }
};

typedef int (* func)(int );
class B
{
    func m_addr;
public:
    B(func param)
        : m_addr(param)
    {

    }
    void execute()
    {
        cout << m_addr(9) << endl;
    }
};

I'm trying to use them like this:

C++

/* error C2355: 'this' : can only be referenced inside non-static member functions error C2064: term does not evaluate to a function taking 1 arguments class does not define an 'operator()' or a user defined conversion operator to a pointer-to-function or reference-to-function that takes appropriate number of arguments */
A a;
B b(A::aFun); 
b.execute();

after googled a lot, i found that std::mem_fun may be helpful. but i don't know how to use it. anyone can help me?

PS: i'm using Visual C++ 2010

Re: can i use mem_fun like this?

Richard MacCutchan1-Dec-12 20:56

Richard MacCutchan

1-Dec-12 20:56

I think the function needs to be a class function (i.e. static).

One of these days I'm going to think of a really clever signature.

Re: can i use mem_fun like this?

Stephen Hewitt2-Dec-12 4:45

Stephen Hewitt

2-Dec-12 4:45

The code doesn't make a lot of sense. The is no connection between the member function to be called and a specific instance of A on which to call it. Also the typedef is incorrect for a non-static member function, make it look likes this:

typedef int (* A::func)(int );

Steve

Re: can i use mem_fun like this?

troyxyz2-Dec-12 6:21

troyxyz

2-Dec-12 6:21

A::aFun is different from func.

Re: can i use mem_fun like this?

Stefan_Lang3-Dec-12 2:14

Stefan_Lang

3-Dec-12 2:14

When you think about it, what you try to achieve isn't logically possible:

A member function that is not static implicitely takes a pointer to the instance as it's first (hidden) argument, so you cannot encode that as a simple pointer, as you always have to additionally pass that instance-pointer. Class B does not have a pointer to an instance of class A, so it cannot possibly call a member function, whether by pointer or any other mechanic!

When you look at your code, where do you use the object a? Nowhere!

Re: can i use mem_fun like this?

Stefan_Lang3-Dec-12 3:45

Stefan_Lang

3-Dec-12 3:45

P.S.: Your code reminds me of the command design pattern. Maybe you should look that up, there are most certainly impementations around. One of the more recent CP newsletters pointed to an article about it at http://ayende.com/blog/159873/design-patterns-in-the-test-of-time-command[^]

Re: can i use mem_fun like this?

Falconapollo4-Dec-12 14:43

Falconapollo

4-Dec-12 14:43

thank you very much. the command pattern is the perfect solution. Smile | :)

client server for running the program

danielsutopo1-Dec-12 15:09

danielsutopo

1-Dec-12 15:09

Hi all,
I am a beginner in networking, I want to do a project to move my arm robot in the server (it is mac) with my p5 glove in the client (it has os window) using client server udp with c++.

In client site I have visual C to translate the movement of the glove.

In server site there are programs to move the robot in c language.

I want to ask, how to send the data/information from the glove to move the arm.

Thank you

daniel

Re: client server for running the program

Albert Holguin1-Dec-12 17:22

Albert Holguin

1-Dec-12 17:22

First off... for something like this, I wouldn't use UDP, I would use TCP/IP. There's really no reason to use UDP, which sends datagrams with no built-in error checking, TCP/IP already handles the error checking/handling (i.e. it'll automatically retransmit packets that didn't arrive at their destination correctly). Usually you only want to use UDP when you have something that doesn't require reliability like voice or video (i.e. if you lose a packet here and there it won't really matter, you'll still be able to hear/see the other person).

As far as sending the data, if you're making for the server and client, it's easy, you define the data messages/structures that are being passed between both completely yourself (via what is typically referred to as an API). Usually the packets are made up of binary buffers, within that buffer, you can either have fixed length or variable length data buffers (or packets), the structure of which is completely up to you.

For example, you can specify:
0. first 4-bytes of the buffer define the message type
1. next 4-bytes define a message specification
2. next 4-bytes define the message size
3. so on...

In this scenario, when you receive a packet, first thing you'll do is cast it onto a data structure that is defined by your API. The first portion of the structure would be an int type (picked it because it's 4-bytes in a 32bit system) and it can specify the type of message that is contained in that data packet. The next portion can be a subset of that message and so on.

Search google and CodeProject for client/server examples and see how they defined their messages.

Limiting selected checkbox items in a CListCtrl

softwaremonkey1-Dec-12 1:40

softwaremonkey

1-Dec-12 1:40

I have a CListCtrl with the LVS_EX_CHECKBOXES style and I want to limit the number of items that the user can select. I have written the following code but (of course) it gets itself in a loop because in changing the state of an item, it causes OnItemchangingLoadingValues() to be called again.

C++

void CSpecimenLoadingDialog::OnItemchangingLoadingValues(NMHDR* pNMHDR, LRESULT* pResult) 
{
	NM_LISTVIEW* pNMListView = (NM_LISTVIEW*)pNMHDR;
	int nCheckedItems = 0;
	for(int i = 0; i < m_loadingVals.GetItemCount(); i++)
	{
		BOOL bState = ListView_GetCheckState(m_loadingVals.m_hWnd, i);
		if(bState)
		{
			nCheckedItems++;
		}
	}

	if(nCheckedItems == 2)
	{
		ListView_SetItemState(m_loadingVals.m_hWnd, pNMListView->iItem, FALSE, LVIS_STATEIMAGEMASK);
	}

	*pResult = 0;
}

What is the correct way to go about doing this? Unsure | :~

Re: Limiting selected checkbox items in a CListCtrl

David Crow1-Dec-12 3:51

David Crow

1-Dec-12 3:51

softwaremonkey wrote:
because in changing the state of an item, it causes OnItemchangingLoadingValues() to be called again.

But the parameters (i.e., state) passed each time are different.

Rather than use a for() loop each time an item's state changes, simply check the state passed and use a counter. Then in OnItemchangingLoadingValues(), you could have something like:

void CSpecimenLoadingDialog::OnItemchangingLoadingValues(NMHDR* pNMHDR, LRESULT* pResult)
{
    if (nCheckedItems < 2)
    {
        if (pNMHDR's new state equals checked)
            nCheckedItems++;
        else
            nCheckedItems--;
    }
}

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Re: Limiting selected checkbox items in a CListCtrl

Jochen Arndt1-Dec-12 23:56

Jochen Arndt

1-Dec-12 23:56

You may add a member variable to your class (or a static variable to the handler function) indicating that the handler is called recursive:

C++

 // Header file
private:
    m_bIgnoreChgHandling;

// Source file
CSpecimenLoadingDialog::CSpecimenLoadingDialog()
{
    m_bIgnoreChgHandling = false;
}

void CSpecimenLoadingDialog::OnItemchangingLoadingValues(NMHDR* pNMHDR, LRESULT* pResult) 
{
    // Alternative: Use static variable here
    // static bool m_bIgnoreChgHandling = false;
    if (!m_bIgnoreChgHandling)
    {
        NM_LISTVIEW* pNMListView = (NM_LISTVIEW*)pNMHDR;
        int nCheckedItems = 0;
        // some handling code
        if(nCheckedItems == 2)
        {
            m_bIgnoreChgHandling = true;
            ListView_SetItemState(m_loadingVals.m_hWnd, pNMListView->iItem, FALSE, LVIS_STATEIMAGEMASK);
            m_bIgnoreChgHandling = false;
        }
    }
    *pResult = 0;
}

Re: Limiting selected checkbox items in a CListCtrl

softwaremonkey2-Dec-12 22:45

softwaremonkey

2-Dec-12 22:45

Clever stuff - thanks Thumbs Up | :thumbsup:

Using VISUAL C++ 6.0 with OLE

ForNow30-Nov-12 9:06

ForNow

30-Nov-12 9:06

Hi,

At work I only have Visual C++ 6.0 this seems like old compiler as everyone is using Visual Studio

I have to automate the importing of data from a .txt file to an EXCEL spreadsheet

I think using OLE is the answer

My question is, is this do-able with Visual C++ 6.0

Thanks

Re: Using VISUAL C++ 6.0 with OLE

jschell30-Nov-12 10:46

jschell

30-Nov-12 10:46

Excel, at least recent ones, can open a CSV file.

So presuming the txt file isn't already CSV all you would need to do is read it, parse it, then output in in CSV.

Re: Using VISUAL C++ 6.0 with OLE

David Crow30-Nov-12 14:24

David Crow

30-Nov-12 14:24

ForNow wrote:

My question is, is this do-able with Visual C++ 6.0

See if this gives you any ideas.

Re: Using VISUAL C++ 6.0 with OLE

ForNow4-Dec-12 13:48

ForNow

4-Dec-12 13:48

I am using the wizard to set up this app the program will go to the DATA menu selection on the EXCEL spreadsheet and select import external data

My question when using the wizard to set up the project will the selection be ATL COM AppWizard or WIN32 console application

Re: Using VISUAL C++ 6.0 with OLE

Stephen Hewitt2-Dec-12 4:54

Stephen Hewitt

2-Dec-12 4:54

Visual C++ 6 will do the job just fine.

Steve

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