C / C++ / MFC

Re: Exception object destroyed 3 times?

14-Oct-04 5:36

Hello,

Consider the following code:

<br />
class A<br />
{<br />
public:<br />
  A() {}<br />
  ~A() <br />
  { <br />
    static int i = 0;<br />
    std::cout << "Destructor called " << ++i << " time(s)" <br />
              << std::endl;<br />
  }<br />
};<br />
<br />
void main()<br />
{<br />
    try<br />
    {<br />
       throw A;<br />
    }<br />
    catch(A ex)<br />
    {<br />
    } <br />
}<br />

When I run the code, the output is the following:
Destructor called 1 time(s)
Destructor called 2 time(s)
Destructor called 3 time(s)
Press any key to continue

I can figure why the destructor is called 2 times, but why is it called the 3d time??? Confused | :confused:

Multiply it by infinity and take it beyond eternity and you'll still have no idea about what I'm talking about.

John M. Drescher14-Oct-04 6:25

John M. Drescher

14-Oct-04 6:25

It has to do with how many times the object is being copied. If you replace the code with the following it will only call the destructor 2 times:

class A
{
public:
A() {}
~A()
{
static int i = 0;
std::cout << "Destructor called " << ++i << " time(s)"
<< std::endl;
}
};

void main()
{
try
{
throw A();
}
catch(A & ex)
{
}
}

[EDIT]

Here is a version that will only be called once:

class A
{
public:
A() {}
~A()
{
static int i = 0;
std::cout << "Destructor called " << ++i << " time(s)"
<< std::endl;
}
};

void main()
{
try
{
throw new A();
}
catch(A * pEx)
{
delete pEx;
}
}

[/EDIT]

John

Re: Exception object destroyed 3 times?

Bob Stanneveld14-Oct-04 6:31

Cleanup of exception objects?

14-Oct-04 6:31

Thanks, this solved my issue with handles getting closed to often Big Grin | :-D

Multiply it by infinity and take it beyond eternity and you'll still have no idea about what I'm talking about.

Errors C2371 and C2512.

Cleber Marinho14-Oct-04 4:49

Cleber Marinho

14-Oct-04 4:49

Please, could someone explain me why there are errors in the following code?

#include <iostream>
#include <string>
using namespace std;

class Log
{
public:
explicit Log(const string& msg) { cout << msg << endl; }
};

int main()
{
string msg = "Hello, World!";

Log(msg.c_str()); // This Works...
Log(msg); // ... but this doesn't; Errors C2371 and C2512!

return 0;
}

I'm using VC++ .NET 2003.

Thanks in advance.

Bob Stanneveld14-Oct-04 3:44

14-Oct-04 3:44

Hello,

I, once again, am wondering about some C++ thing. This time it is about the cleanup of thrown exceptions.

Consider the following code:

<br />
// in some function an error condition is met<br />
throw new CSomeException(ErrorNumber);<br />
<br />
// in a try-catch block the exception is caught like this<br />
catch(CSomeException *pEx)<br />
{<br />
  // handle exception, don't call delete on pEx!<br />
}<br />

I want to know if the destructor is called when the catch-block is left, or does this lead to a memory leak?

Multiply it by infinity and take it beyond eternity and you'll still have no idea about what I'm talking about.

Nathan Holt at EMOM14-Oct-04 5:06

Nathan Holt at EMOM

14-Oct-04 5:06

Bob Stanneveld wrote:
I want to know if the destructor is called when the catch-block is left, or does this lead to a memory leak?

It leads to a memory leak. If someone throws a pointer to an exception, it won't automatically be deleted.

Nathan Holt

Bob Stanneveld14-Oct-04 5:16

14-Oct-04 5:16

Hello,

Thanks for the information. Big Grin | :-D

Multiply it by infinity and take it beyond eternity and you'll still have no idea about what I'm talking about.

Cleber Marinho14-Oct-04 5:11

Cleber Marinho

14-Oct-04 5:11

You can know this by yourself debugging. Put a breakpoint in your descructor, for exemple.

Bob Stanneveld14-Oct-04 5:21

char array -> system::string

14-Oct-04 5:21

I know, but I'm always looking for an excuse to surf to codeproject.com Poke tongue | ;-P

Multiply it by infinity and take it beyond eternity and you'll still have no idea about what I'm talking about.

Darcy P14-Oct-04 2:57

Darcy P

14-Oct-04 2:57

Hello, I'm using VC++ .NET 2003 and I'm fairly new to it and to GUI programming in general. For my current project I need to interact with some legacy C code that uses character arrays for strings.

I was able to convert from a system::string to a character array using the "PtrToStringChars" method but I can't, for the life of me, figure out how to convert an old-school char array back into a system::string.

Oh and the reasoning is that basically I need to parse a textbox in my form, convert the contents to a char array for the c code, then take a char array returned by the c code and convert it back to a managed string to be displayed in another textbox on the form. Make sense?

So... how do I do it!? Smile | :)

CString problem

Anonymous14-Oct-04 2:33

Anonymous

14-Oct-04 2:33

Dear Friends,

I got a CString. What i want to find out is whether the first character in that CString is a Number (i.e 0 to 9). How can i do so ??

David Crow14-Oct-04 2:42

David Crow

14-Oct-04 2:42

Use isdigit().

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

BlackDice14-Oct-04 3:01

BlackDice

14-Oct-04 3:01

Yes, use IsDigit(), and you can reference the first character of a CString like a char array (ie mystring[0])

[A brave person isn't always necessarily a smart person]

bdiamond Sleepy | :zzz:

Bob Stanneveld14-Oct-04 3:33

14-Oct-04 3:33

Yep

Multiply it by infinity and take it beyond eternity and you'll still have no idea about what I'm talking about.

Linking a C# dll into C++

hyling14-Oct-04 4:17

hyling

14-Oct-04 4:17

Cool!! Didn't know you could access it like an array. Big Grin | :-D

Member 131514814-Oct-04 2:21

Member 1315148

14-Oct-04 2:21

Does anyone know how to run a C# procedure that is located in a dll from a C++ .net dll?

Thanks
Max

DirectX CreateSurface question

Cedric Moonen14-Oct-04 2:03

Cedric Moonen

14-Oct-04 2:03

Hello !

I just started DirectX programming (based on samples I found on several websites). In fact I want to make a game (so in fullscreen mode). Everything is ok for that part but the problem when using this exclusive & fullscreen mode is that you cannot debug anymore (the screen remains black when a break point is reached in your code).

So I wanted to first start by using a windowed game for debugging purpose. But there the problem is when I try to create the front buffer using CreateSurface (with CooperativeLevel flags set to DDSCL_NORMAL):

     DDSURFACEDESC2		ddsd;<br />
   ZeroMemory( &ddsd, sizeof( ddsd ) );<br />
<br />
    ddsd.dwSize = sizeof( ddsd );<br />
    ddsd.dwFlags = DDSD_CAPS | DDSD_BACKBUFFERCOUNT;<br />
    <br />
	ddsd.ddsCaps.dwCaps = DDSCAPS_PRIMARYSURFACE |<br />
                          DDSCAPS_FLIP |<br />
                          DDSCAPS_COMPLEX;<br />
							<br />
    ddsd.dwBackBufferCount = 1;<br />
    <br />
	hRet = m_pDirectDraw->CreateSurface(&ddsd, &m_pFrontBuffer, NULL );

The function returns DDERR_NOEXCLUSIVEMODE ...

How can I solve the problem ??

BlackDice14-Oct-04 3:03

BlackDice

14-Oct-04 3:03

I recall having that same problem before about breakpoints in fullscreen mode. I think you can alt+tab or something like that to get back to the development environment.

[A brave person isn't always necessarily a smart person]

bdiamond Sleepy | :zzz:

Cedric Moonen14-Oct-04 3:11

Cedric Moonen

14-Oct-04 3:11

No, in fact what happens is that when I reached a breakpoint, I can see the taskbar but the rest of the screen is still black (wathever I do, also using alt+tab...). This is quite annoying Mad | :mad:

Antony M Kancidrowski14-Oct-04 4:12

Antony M Kancidrowski

14-Oct-04 4:12

You may want to invest in a second monitor. You can then run the IDE on the second monitor and debug your DirectX application on the first monitor.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

Cedric Moonen14-Oct-04 4:31

Cedric Moonen

14-Oct-04 4:31

Mhh, yes that could be a solution but this project is just for spare time and so, I don't want to buy a second monitor just for that...
Isn't it possible to debug DirectX applications ????