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yes u can call one constructor from an another constructor.....
class xyz
{
.....
....
...
..
.
xyz()
{
i
}
xyz(int j)
{
xyz();
..
.
}
};
"faith, hope, love remain, these three.....; but the greatest of these is love" -1 Corinthians 13:13
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Sorry, but that link is not correct. at least not completely.
The way to call one constructor from another is to use "placement new".
For example:
Foo::Foo()
{
int i;
new (this)Foo(i); // this will call the Foo::Foo(int) ctor without allocating memory
}
Foo::Foo(int)
{
}
This begs the question of why you want to do this. If it is for "common" initialization code, the better answer is to have a separate initialization function, as in the following. Then call that init code either from each ctor, or perhaps better, to call it from the places where Foo is constructed. then maybe handle init failures there.
bool Foo:init(some parameters here maybe)
{
// do init code here
}
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Actually, you can call a constructor from the object itself. A constructor is just another function/method, but is called by the memory allocation scheme (IE: Operator new).
You can also call the destructor any time you want, as a standard object method (EX: pMyObj->~MyObject(); ).
Why would you want to do this? Consider the following: You want to allocate memory dynamically in a busy, multithreaded environment. Therefore, you want to avoid the heap. So, you decide dynamically allocate memory from the stack using _alloca(). In order to initialize this "object", you need to call the constructor. Also, when you are finished with this object, you MUST NOT "delete" it, but you should destroy it properly by calling the destructor.
A non-tested example for thought purposes:
#define STACK_OBJECT_NEW(c, p) {p = (c *)_alloca(sizeof(c)); if (p) p->c(); }
#define STACK_OBJECT_DELETE(c, p) {if (p) p->~c(); }
void MyFunc()
{
MyClass *p = NULL;
STACK_OBJECT_NEW(MyClass, p);
if (p)
{
p->InvokeSomeMethod();
...
STACK_OBJECT_DELETE(MyClass, p);
}
}
onwards and upwards...
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We all know now that you are a guru. But keep the hack to yourself next time!
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you don't like my "hack"? 
onwards and upwards...
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ahz wrote:
The way to call one constructor from another is to use "placement new".
This is incorrect.
Herb Sutter - the current chairman of the C++ standards committee described this 'anti-idiom' as 'an abomination' and 'abhorrent' in the article 'delegating constructors' C/C++ Users Journal May 2003. For any data members that are not POD, this approach will fail, because the destructor of that data members will run only once, while the constructors will have run twice
To the initial poster. The only way to solve this problem is with an initialization function, but you must also ensure that that function is not virtual.
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It may be frowned upon, and may even be abhorent, but is it not incorrect.
The original poster asked a simple direct technical question and I gave a simple direct techinically correct answer.
It is correct C++ syntax, it is technically correct, and it works --- albeit for simple cases.
I wouldn't use it, and don't recommend it --- for Herb Sutters reasons --- and for many of my own reasons that I won't belabor here.
However, I agree the best way to solve the issue is with an initialization function. However, I don't think it necessarily needs to be non-virtual. Depends on where you are calling the function from. If from the ctor, then yes make sure it's non-virtual. If from outside the ctor (the method I recommend, then it's ok to be virtual).
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ahz wrote:
It may be frowned upon, and may even be abhorent, but is it not incorrect.
The original poster asked a simple direct technical question and I gave a simple direct techinically correct answer.
Wrong, wrong, wrong   
From: http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.3[^]
<quote>
"BTW do NOT try to achieve this via placement new. Some people think they can say new(this) Foo(x, int(x)+7) within the body of Foo::Foo(char). However that is bad, bad, bad. Please don't write me and tell me that it seems to work on your particular version of your particular compiler; it's bad. Constructors do a bunch of little magical things behind the scenes, but that bad technique steps on those partially constructed bits. Just say no."
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I guess you can't read.
It is correct.
Whether you should do it is another thing altogether.
LEARN TO READ!
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I would recommend going the way of the Initialize() method. It will make your code much easier to debug two years from now on a late, dark, rainy night with a customer expecting a bug fix early the next morning.
/ravi
My new year's resolution: 2048 x 1536
Home | Articles | Freeware | Music
ravib@ravib.com
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I'm looking for something like "End process tree" form task manager.
I start an application using ShellExecuteEx. I have its handle and TerminateProcess works just fine, however aplication starts its own processes which remain. Sending WM_QUIT message doesn't work at all. Question is how can I kill whole process tree?
I don't care about proper shutwown, so even "brute force" metods will do fine.
thanks for any help
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How i Hack registry Files
Plz Help me Friends
I m working on a application Registry Hacking i read all values from Registry Files into diffrent Data structures like regf, hbin, cellData(nk,vk,sk,lf,li) in these dataStructures but still i dont know how i interpret these values in understandable or readable format
if any one know abt that plz help me
shahzad Ahmed
shahzi77@yahoo.com
I Develope On Software on Netmeeting Com API in this i have Problem is When i am Dial a Call Using Following Line of Code
ULONG ulOptions=M_INIT_CONTROL;
HRESULT Initialize(ULONG *uOptions,ULONG *Reserved);
After Some Line of Code
When I Call the Following Line in our Code
INmManager::CreateCall(INmCall**ppCall,NM_CALL_TYPE callType,NM_ADDR_TYPE uType, BSTR bstrAddr, INmConference
pConference);
then the Netmeeting Dialing Progress bar are Visible on the Screen i want that bar was not
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How i Hack registry Files
Plz Help me Friends
I m working on a application Registry Hacking i read all values from Registry Files into diffrent Data structures like regf, hbin, cellData(nk,vk,sk,lf,li) in these dataStructures but still i dont know how i interpret these values in understandable or readable format
if any one know abt that plz help me
shahzad Ahmed
shahzi77@yahoo.com
I Develope On Software on Netmeeting Com API in this i have Problem is When i am Dial a Call Using Following Line of Code
ULONG ulOptions=M_INIT_CONTROL;
HRESULT Initialize(ULONG *uOptions,ULONG *Reserved);
After Some Line of Code
When I Call the Following Line in our Code
INmManager::CreateCall(INmCall**ppCall,NM_CALL_TYPE callType,NM_ADDR_TYPE uType, BSTR bstrAddr, INmConference
pConference);
then the Netmeeting Dialing Progress bar are Visible on the Screen i want that bar was not
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What do you mean by "hack the registry?" If you want to read from or write to the registry, why not use the intended functions?
"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow
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Hi,
I'm trying to display the icons of some folders in a ListCtrl and it's all ok except the first icon. This one appears with a black shadow  and the rest are displayed correctly.
My code is this:
HIMAGELIST hList = ImageList_Create(32,32, ILC_COLOR32|ILC_MASK , 0, 100);
m_ImageList.Attach(hList);
m_ImageList.SetBkColor(ILD_TRANSPARENT);
for (i=0;i<num;i++)
{
SHGetFileInfo(path, FILE_ATTRIBUTE_NORMAL, &shfileinfo, sizeof(shfileinfo), SHGFI_DISPLAYNAME|SHGFI_ICON);
m_ImageList.Add(shfileinfo.hIcon);
m_listFile.SetImageList(&m_ImageList, LVSIL_NORMAL);
lvi.mask = LVIF_IMAGE | LVIF_TEXT;
lvi.iItem = i;
lvi.iSubItem = 0;
lvi.pszText = shfileinfo.szDisplayName;
lvi.iImage = i;
::DestroyIcon(shfileinfo.hIcon);
m_listFile.InsertItem(&lvi);
}
Does anybody know why occurs this? 
Thanks in advance!
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Mr DAVID CROW
IS IT NECESSARY TO WRITE Extern"C" IN THE DEFINATION OF A FUNCTION(EXPORT FUNCTION) IN A DLL EXTENSION MFC.ACCORDING TO ME IT IS MEANINGLESS AS THESE DLLS CAN ONLY BE USED BY MFC APPLICATION.
TO MY PREVIOUS QUERY U SENT ME A MAIL.BUT I DELETED THAT MESSAGE.IF U DONT MIND CAN I GET UR EMAIL ADDRESS.PLS SENT THE ANS TO MY PREVIOUS QUERY.IT WAS,USING CREATEPROCESS() CAN I DO SILIENT SETUP OF .EXE FILE.I DOWNLOADED A WINZIP FILE USING URLOPEN()AND THEN RUN THE PROGRAM USING CREATE PROCESS().IT IS SHOWING ME THE SETUP OF WINZIP.I WANT TO HIDE THIS SETUP FROM USER.
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EVEN IF I USE _declspec(dllexport) ,it is of no use to define the exxported function with extern"C".AS THERE NO INTERFACE PROBLEM DLL EXTENSION AND APPLICATION
but it is must in DLL Regular
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Hi, I've not found any information on this anywhere, so any ideas you can give me will be helpful.
I'm using Visual Studio .net 2003, and I have a problem.
The problem is, whenever I try to view the contents of a struct that i've allocated whilst stepping through the code, every part of it appears to be undefined, yet, when the code accesses it, and prints various bits, it works fine. It just appears to be a problem of the debugger attaching to it.
The situation is this. I have one large struct that contains sub structs. I allocate sub structs on a per required basis, initializing the memory to zero after allocating it.
My Project uses C# as a front end, and c++ with .net extensions as a DLL. The DLL isn't really c++, but is C code compiled as C++ (using the project properties), so doesn't use any classes.
It is quite a large project, with the main file running to 5,000 lines, so I don't want to undertake a conversion to C++ .net without knowing that there is nothing I can do to avoid it.
To me, it appears to be a debugger problem. Are there settings that control this sort of thing?
Any ideas?
Thanks,
Dave Smith
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Dave J Smith wrote:
The problem is, whenever I try to view the contents of a struct that i've allocated whilst stepping through the code, every part of it appears to be undefined, yet, when the code accesses it, and prints various bits, it works fine. It just appears to be a problem of the debugger attaching to it
You must initialize the struct, preferably by using new and a constructor instead of malloc. It's not a problem, It's just C++.
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Hi,
when I use remove("c:\test.txt") the file is deleted, but can still be found in the recycle bin.
Is there a way to delete a file permanently ?? So that it is removed but not into the recycle bin ?
THx
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I think you must have confused yourself, because remove simply calls DeleteFile, which does not move items into the Recycle Bin.
Perhaps you have a program running which intercepts file deletions?
Stability. What an interesting concept. -- Chris Maunder
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