C / C++ / MFC

Re: CComboBox for lots and lots of options

4-Dec-12 21:15

Mattias G wrote:
there should definitely be someone out there having solved it.

Well I guess not since you can't find a sample.

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

Rolf Kristensen5-Dec-12 7:13

Rolf Kristensen

5-Dec-12 7:13

If you could find a ComboBox that expands into CListCtrl, then you can use the grouping feature of the CListCtrl.

But an easier solution is just to use two ComboBoxes. One that allows one to select user type, and one that displays the filtered result within the selected user type.

CString assignment crashes on Windows 7

pandit843-Dec-12 3:57

3-Dec-12 3:57

Hi
I have a function

void TakeData(myStruct &structRef)
{
  CString str = TmpFileMgr->TmpFilePathName() ; //Returns file path 
  structRef.cstrFilePath = str ;                //Crashes at this point on Windows 7
}

in a dll which takes Temporary folder path and assign it in a CString variables. This CString variable is member of structure object which is passed as a reference to TakeData(myStruct &structRef)function.
I am able to print temporary folder path in TakeData function and CString assigment works perfectly on Windows XP. But when I run this code on Windows 7 it crashes at the point where I am doing assigment of temp folder path in a CString variable. I have all admin rights on Windows 7 System , also I have put UAC to OFF.

Please provide any input in this regard. Thanks

modified 3-Dec-12 10:16am.

David Crow3-Dec-12 4:08

David Crow

3-Dec-12 4:08

pandit84 wrote:
But when I run this code on Windows 7 it crashes at the point where I am doing assigment of temp folder path in a CString variable.

And yet this is the code you do not show. If TakeData() is not pages long, please post it.

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CPallini3-Dec-12 4:15

CPallini

3-Dec-12 4:15

I suppose this is worth reading: "Using and Writing DLLs with MFC"[^].

Veni, vidi, vici.

Richard MacCutchan3-Dec-12 5:02

3-Dec-12 5:02

What is the definition of myStruct, and what is the value of structRef when the crash occurs?

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

pandit843-Dec-12 5:41

3-Dec-12 5:41

Struct is defined as below. Before crash ,value of cstrFilePath is empty.

struct myStruct
{
	int charsize ;	 
	CString	cstrFilePath;
	myStruct() : charsize (0)
	{
	    cstrFilePath.Empty();
	}
} ;

Richard MacCutchan3-Dec-12 6:22

3-Dec-12 6:22

pandit84 wrote:
Before crash ,value of cstrFilePath is empty.

Which is rather irrelevant. What I asked was, what is the value of structRef when the crash occurs?

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

Stephen Hewitt4-Dec-12 6:34

4-Dec-12 6:34

You have supplied very little to go on, so in addition to suggesting you provide more information I'll ask a question: are you allocating memory in one module and freeing it in another (a module is a dll or exe)?

Steve

pandit844-Dec-12 19:44

4-Dec-12 19:44

I am sorry for adding incomplete info.
I have allocated memory to object of structure myStruct in one dll and passed this struct object as a reference to another dll. This crash happens only while assinging value to

C++

structRef.cstrFilePath

variable. Finally I was able to assign value inside CString variable using

C++

wsccpy

method. I was able to resolve this crash with following code , but I am sure this is not the correct way to do it.

C++

wcscpy (structRef.cstrFilePath.GetBuffer (), str.GetBuffer ()) ;

I am still trying to resolve this issue in a correct way. I am using Windows 7 system and GCC Compiler. Thanks all for replying to my previous post.

Stephen Hewitt5-Dec-12 3:49

5-Dec-12 3:49

Unless you configure things properly each module (dll or exe or other executable module) has it's own heap. In this environment you can't allocate memory in one module and free it another. Given that CString manages a buffer using an instance in multiple modules could result in this happening. Forget wcscpy, it's ugly and isn't a fix for the root problem, whatever it is. If it's heap corruption, which is my guess, it's going to blow up sooner or later and "fixing" one problem with an ugly hack will just result in it popping up somewhere else.

Steve

modified 5-Dec-12 11:14am.

pandit8418-Dec-12 7:48

18-Dec-12 7:48

Finally I have solved this issue.
The CString when used with GCC was Used as LinuxCString which is internally std::string. Capacity of std::string when calculated was every time 0. so when I tried to assign const char* to LinuxCString ( i.e. CString in MSVC ) it was crashing.

I have used std::string.reserve (200) method to specify the capacity first while initialization. This solves my issue.
I am still evaluating whether my fix is perfect or not.

Thanks all

Stephen Hewitt18-Dec-12 17:44

Segmentation Fault in GTK library files

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

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

Richard MacCutchan2-Dec-12 21:47

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.

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

Richard MacCutchan2-Dec-12 22:28

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.

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

Richard MacCutchan3-Dec-12 0:55

can i use mem_fun like this?

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.

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

Richard MacCutchan1-Dec-12 20:56

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.

Stephen Hewitt2-Dec-12 4:45

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

troyxyz2-Dec-12 6:21

troyxyz

2-Dec-12 6:21

A::aFun is different from func.