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HoDuc wrote:
Will the memmory block(contains 200 bytes of str)
which is pointed to by pT be free(deallocated) when we leave the function
no, it will free when a call of delete[] occurs, of when main leaves (and so, the system destroys the array)
HoDuc wrote:
What happens inside (when deallocating)?
if calls the destructors of each object in the tab before freeing the memory space... (soory, wrong)
it free the memory, even though the objects were "destructed"
TOXCCT >>> GEII power
[toxcct][VisualCalc]
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T::T()
{str=new char[200];
}
void f()
{T* pT=new T();//no need to mention braces
}
in destructor u do the opposite of u did in CONSTRUCTOR
SO MENTION A DESTRUCTOR
T:~T()
{delete[] str;
}
in the void f()
delete pT; //mention in the f() where u dont require the
//pointer usually at the end of f()
which will call the above destructor
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sunit5 wrote:
in destructor u do the opposite of u did in CONSTRUCTOR
No, not necessarily !! If you allocated your str elsewhere than in your constructor (and it happens very very often for me), you will have a memory leak then, because if I follow your rule, it won't be delete then...
Another thing: make 'safe destructions' before deleting an object, check if the pointer is not NULL, then delete the object and after that make it NULL (not really necessary but better be too much protective than the opposite  ). And also, if your pointer is not allocated in the constructor, make it NULL so if it has not been yet allocated when your object is destroyed, it will not be deleted (and the opposite will result of a very very bad error message  ).
So, a general rule I follow in my destructor: use this safe destruction for all pointers in your object and this is ok.
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There is no point in part one of your safe destruction idea. The C++ delete operator takes care of the case where the pointer is NULL. So delete(NULL) is legal and does nothing. I do agree with your other ideas though, they are very helpful. Especially the bit about setting pointers to NULL on initialization..
Regards
Senthil
_____________________________
My Blog | My Articles | WinMacro
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I had serious doubts about your statement, "The C++ delete operator takes care of the case where the pointer is NULL." So I did some digging in the CRT library source. It turns out that this statement is not totally correct. The C++ delete operator just ends up calling _free_dbg and that checks for a null pointer. In the end the null pointer is caught though and that is the bottom line.
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Rick York wrote:
I had serious doubts about your statement, "The C++ delete operator takes care of the case where the pointer is NULL." So I did some digging in the CRT library source. It turns out that this statement is not totally correct. The C++ delete operator just ends up calling _free_dbg and that checks for a null pointer. In the end the null pointer is caught though and that is the bottom line.
The C++ standard dictates that the delete operator must handle a NULL pointer being passed to it correctly. It makes no difference where, it will always be the case for a reasonably standards-compliant compiler/library (I don't know of any which don't obey this)
Ryan "Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"
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I checked VC++ 7.1's CRT implementation, it does check for NULL and return immediately (dbgdel.cpp, line 42). What compiler are you using?
I think it is just an inefficient implementation of the standard. The C++ standard pretty clearly says that the delete operator must handle the NULL pointer case.
Regards
Senthil
_____________________________
My Blog | My Articles | WinMacro
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Hi all
In my dialog, i've many objects that are a RichEditCtrl, an some buttons.
I create with ClassWizard to add OnNotify in my app.
BOOL CCEdataTextEditorDlg::OnNotify(WPARAM wParam, LPARAM lParam, LRESULT* pResult) <br />
{<br />
if( wParam == IDC_RICH )
{<br />
MessageBox("Non");
}<br />
MessageBox("hic");
<br />
return CDialog::OnNotify(wParam, lParam, pResult);<br />
}
But i get nothing!!
plz, help me! thanks for all
hzocm
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Just to confirm... you are definitly getting no notifications? For example - try typing something, then select some of the text you typed. The selecting sould generate a notification event.
Joel Holdsworth
Wanna give me a job this summer?
Check out my online CV and project history[^]
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no, there are nothing!
u know, in the end, that means after if (wParam == IDC_RICH){...}, we've MessageBox("blabla")
but it doesn't launch!
plz, help me!! 
hzocm
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Another possibility is that the notification messages are only routed to the specific event handlers. If you look in the class wizard, you should see events that are associated with this control only. Try adding handlers for these, and see if you get any luck.
Joel Holdsworth
Wanna give me a job this summer?
Check out my online CV and project history[^]
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Have you used SetEventMask() to tell the rich edit control to send notifications? If you don't it won't send any.
Ryan "Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"
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great!!!!!
thanks for your help and Joel Holdsworth too!
hzocm
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Hi All,
I wonder who can tell me how to pass a string in DLL? For example, if I make 2 func as:
int IntTest()
{
int loc_int;
loc_int = 123;
return loc_int;
}
char *StrTest()
{
strcpy(glob_buf, "Hello from DLL");
return glob_buf;
}
In these 2 funcs, IntTest() works; but StrTest() does not despite it trys to pass a global buffer defined in header file. I used the DLL in my VB application, StrTest() did not work out(no hello-string appeared), but no error popped out.
Anybody can help me out? Any kind of hint is appreciated!
Huey 
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Hi All,
I wonder who can tell me how to pass a string in DLL? For example, if I make 2 func as:
int IntTest()
{
int loc_int;
loc_int = 123;
return loc_int;
}
char *StrTest()
{
strcpy(glob_buf, "Hello fro DLL");
return glob_buf;
}
In these 2 funcs, IntTest() works; but StrTest() does not despite it trys to pass a global buffer defined in header file. I used the DLL in my VB application, StrTest() did not work out(no hello-string appeared), but no error popped out.
Anybody can help me out? Any kind of hint is appreciated!
Huey
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you must say somewhere in you dll that glob_buf is defined (see extern keyword).
otherwise, why not making this :
char* StrTest() {
char* Buff = new char[14];
::strcpy(Buff, "Hell from DLL");
return Buff;
}
TOXCCT >>> GEII power
[toxcct][VisualCalc]
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Are you sure this will work ??
You try to write something at a NULL adress
Ok, but in fact the problem is not there. The problem is that VB and C++ don't use the same standard from strings. C++ uses zero-terminated strings and VB uses a kind of BSTR string (the length of the string is stored at the begning, each char takes 2 bytes and it is not zero-terminated).
You need to use a BSTR string inside your function and return it. I know this is a tricky problem and I spent a lot of time on this to find out a solution.
Sorry but I don't remeber exactly of the implementation details but take a look at BSTR strings (specifically this[^] article (and the functions at the end)
Hope this helps
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This solution won't work neither
You will allocate memory in your dll and then return this string in the program. Two solutions: you don't delete the string -> this will result in a memory leak OR you delete the string and this will result in a runtime error because one basic rule is that the memory allocated by one process must be freed by the same process !! So here you allocate the string in the dll and free it in your program 
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If I understand your problem, you should allocate a string in the main process and pass his pointer to the dll function. In the dll function you can copy the string and then return to main process.
<br />
{<br />
char* str;<br />
str = new char[50];<br />
dll_func(str,50);<br />
<br />
<br />
}<br />
<br />
<br />
void dll_func(char* str, int max_size)<br />
{<br />
strcpy(str,"hallo world!");<br />
return;<br />
}<br />
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Your idea was right as was your comment but your implementation does not use the max_size parameter. Shouldn't that be : strncpy( str, "hallo world", max_size ); ?
Just to be safe I would write the first part something like this :
<br />
<br />
const int strsize = 50;<br />
char* str;<br />
str = new char[strsize+1];<br />
dll_func(str,strsize);<br />
This way you will reserve a spot for a null character on the end.
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Rick York wrote:
Your idea was right as was your comment but your implementation does not use the max_size parameter.
'couse I'm lazy!  I thought that I solved that problem with my " //use max_size to prevent buffer overflow"
Rick York wrote:
Shouldn't that be : strncpy( str, "hallo world", max_size ); ?
yes.. this should a good implementation. Personally I usually use something like:
<br />
int dll_func(char* str,int max_size)<br />
{<br />
<br />
const char dll_str[] = "hallo world!";
<br />
strncpy(str,"hallo world!",max_size);<br />
return strlen(dll_str);<br />
}<br />
so in main process you can check (if (dll_func(str,strsize) > strsize) ) if you have truncated the string and the real/needed size.
Bye,
Francesco
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Nothing of these will work in current context ! The problem is that the function is called from a VB program ! Thus, the first part will work (you can pass a string from VB in a C++ dll by specify it must be passed by val). But this will crash after when you try to read the string in VB. VB and C++ uses different string types...
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cedric moonen wrote:
But this will crash after when you try to read the string in VB.
Oh.. I missed that!
Well.. I'm not using visual basic but I wrote some dll used by
Delphi programs. We solved the same iusse using simple types like
arrays of int/char instead of complex types like BSTR or pascal's string.
I suppose that you can pass to dll_func a Byte array and then convert it to a string.
Something like:
Dim ByteArrayString(50) As Byte
Here you can find something about bytearray to string conversion in Visual Basic.
Hope this help.
Bye,
Francesco
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Hello All,
The following simple program that uses forward referencing does not
compile in my VC++ 6.0 compiler.
On the line where I define the member function
Pont2D::projectFrom(Point3D p3d) { ... }
the compiler complains that Point3D is undefined and refers to the
declaration at the beginning that tries to forward reference
the Point3D class. Here is the compiler output:
ForwardReference.cpp
ForwardReference.cpp(11) : error C2027: use of undefined type 'Point3D'
ForwardReference.cpp(4) : see declaration of 'Point3D'
ForwardReference.cpp(11) : error C2228: left of '.i' must have class/struct/union type
ForwardReference.cpp(11) : error C2027: use of undefined type 'Point3D'
ForwardReference.cpp(4) : see declaration of 'Point3D'
ForwardReference.cpp(11) : error C2228: left of '.j' must have class/struct/union type
Has any one encountered similar problem? Is there any command line option that would handle this issue?
Thanks.
Ganesh.
// ForwardReference.cpp: The First Line of the file
#include <iostream.h>
class Point3D; // Forward Declaration of class Point3D defined below.
class Point2D {
public:
int i, j;
Point2D() : i(0), j(0) {}
Point2D(int a, int b) : i(a), j(b) {}
void projectFrom(Point3D p3d) { i = p3d.i; j = p3d.j; } // compilation error
};
class Point3D { // being declared above, compiler ignores the defintion here.
public:
int i, j, k;
Point3D() : i(0), j(0) k(0) {}
Point3D(int ii, int jj, int kk) : i(ii), j(jj), k(kk) {}
Point3D& operator=(const Point2D& p2d) { i = p2d.i; j = p2d.j; k = 0;}
};
int main()
{
Point2D p2d(1,2);
Point3D p3d(2,3,4);
p2d.projectFrom(p3d);
cout << "p2d = (" << p2d.i << "' " << p2d.j << ").\n";
return 0;
}
// end ForwardReference.cpp
Ganesh
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did you try to rebuild all your project ?
TOXCCT >>> GEII power
[toxcct][VisualCalc]
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