C / C++ / MFC

jhwurmbach23-Aug-07 21:57

23-Aug-07 21:57

Set a breakpoint right at the top of myview::OnUpdate()

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Iain Clarke, Warrior Programmer

Iain Clarke, Warrior Programmer23-Aug-07 22:00

23-Aug-07 22:00

When it crashes, go into the debugger, and look at the call stack. This will show the sequence of functions (and how far into them you were).

In VC++6, you can get this from the View | Debug Windows | Call Stack menu, or alt-7.

Good luck,

Iain.

jhwurmbach23-Aug-07 23:55

23-Aug-07 23:55

devvvy wrote:
I do know call stack and such.

Its one of the debug-windows. While debugging (e.g. when your program execution stopped on a breakpoint) activate it in the VC++ - "Debug"-menu.

Though I speak with the tongues of men and of angels, and have not money, I am become as a sounding brass, or a tinkling cymbal.
George Orwell, "Keep the Aspidistra Flying", Opening words

jhwurmbach24-Aug-07 0:37

24-Aug-07 0:37

Im sorry - I read your mail above to state "I don't know call stack...".
My fault. Please excuse me.

Though I speak with the tongues of men and of angels, and have not money, I am become as a sounding brass, or a tinkling cymbal.
George Orwell, "Keep the Aspidistra Flying", Opening words

[Message Deleted]

devvvy24-Aug-07 0:47

devvvy

24-Aug-07 0:47

[Message Deleted]

jhwurmbach24-Aug-07 0:52

24-Aug-07 0:52

I did reply to you by mail (using the mail-button below the text). You did not receive my Mail?

As an alternative, could you put the code on some of the free webspace providers and post the adress here?
I am reluctant to post my mail adress here in the open.

Though I speak with the tongues of men and of angels, and have not money, I am become as a sounding brass, or a tinkling cymbal.
George Orwell, "Keep the Aspidistra Flying", Opening words

David Crow24-Aug-07 6:03

David Crow

24-Aug-07 6:03

devvvy wrote:
do you think I can send you the stripped down package?

As a professional, you should not have a need to do this. Simply do as previously suggested and you'll find the exact cause of the problem. The debugger is your friend. It exists for a reason.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

devvvy23-Aug-07 22:50

devvvy

23-Aug-07 22:50

My MFC experience told me sometimes some MFC supplied member/attributes no valid until some sequence completed... using it before hand would crash it...

can't remember the detail now that's just an impression from a difficult bug i had long ago. But yes step thru the code with a debugger will allow you to zoom in on the problem

Jim Crafton24-Aug-07 7:19

Jim Crafton

24-Aug-07 7:19

You mean like, oh, I don't know, maybe creating the resource (HWND, HFONT, HBITMAP, etc) first by calling one of the CreateXXX methods on MFC? Is that what you're referring to?

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static variable

George_George23-Aug-07 19:22

23-Aug-07 19:22

Hello everyone,

I am wondering how C or C++ manages static variable internally. Since each time when we again a function again, if in this function, a static variable is defined, the value will be the value last time when we entered this function (i.e. will not be initialized again, and only initialized at the 1st time).

I suspect it is stored in some global structure to reserve the value?

thanks in advance,
George

User 58385223-Aug-07 19:27

23-Aug-07 19:27

My understanding is that static vars are initialised before main() is called. You could check this by creating a class with a constructor, init a static variable of this type, put a breakpoint in the constructor and see what happens

George_George23-Aug-07 19:35

23-Aug-07 19:35

Thanks Josh,

Do you mean static variable inside a function? If yes, how do you think such *local* static variable will be stored, since normal local variable (value) will vanish after function returns. But for static *local* variable, the value will not vanish -- and will be recorded next time when we entered the same function.

Any ideas or comments?

regards,
George

User 58385223-Aug-07 19:42

23-Aug-07 19:42

I dont know to be honest but I would imagine that all static variables are pushed onto the stack before main() is called and therefore "local" statics dont really go out of scope when a function ends. I suspect the actual details may vary between compilers.

George_George23-Aug-07 20:01

23-Aug-07 20:01

Thanks Josh,

Good answer! I have a further question about programming best practice. Do you think it is safe to let the address of the *local* static variable as the return value of a function? Then other part of code (out of this function) will access or even modify the variable by the returned address of the *local* static variable?

Any disadvantages of this approach?

Example,

<br />
<br />
int* func()<br />
{<br />
    static int i;<br />
    // other code<br />
<br />
    return &i;<br />
}<br />
<br />

regards,
George

ThatsAlok23-Aug-07 20:04

ThatsAlok

23-Aug-07 20:04

when you mark some variable static, compiler wil decide how to treat that variable.. so there no scope of local and global variable concept here!

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George_George23-Aug-07 20:29

23-Aug-07 20:29

Thanks Alok!

If you think static variable is different from local or global variables, how do you think static variable is stored and managed so that the value is reserved each time we enters the function in which the static variable is defined?

regards,
George

User 58385223-Aug-07 20:06

23-Aug-07 20:06

George_George wrote:
Good answer! I have a further question about programming best practice. Do you think it is safe to let the address of the *local* static variable as the return value of a function? Then other part of code (out of this function) will access or even modify the variable by the returned address of the *local* static variable?

Any disadvantages of this approach?

I'd say it smells like bad design, the only reason to return a pointer rather than a copy of the int is to allow some other code to modify it. I'd rather provide a method to allow other code to modify the static.

ThatsAlok23-Aug-07 20:10

ThatsAlok

23-Aug-07 20:10

Josh Gray wrote:
I'd say it smells like bad design, the only reason to return a pointer rather than a copy of the int is to allow some other code to modify it. I'd rather provide a method to allow other code to modify the static.

sorry to interrupt you.. it's somewhat Singleton pattern...! so i don't think it bad design.. though it break OOPS basic concept of encapsulation and abstraction!

cheers,
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User 58385223-Aug-07 20:15

23-Aug-07 20:15

ThatsAlok wrote:
i don't think it bad design.. though it break OOPS basic concept of encapsulation and abstraction!

Which to me makes it bad design. You can still have the static and therefore the singleton pattern but my comments was more about how you expose the interface to it. Returning the address of what is basically a private variable is bad.

George_George23-Aug-07 20:22

23-Aug-07 20:22

Thanks Josh,

I can generally understand and agree with your points. But I am confused about some details. Could you show us your points by a couple of lines of code please?

regards,
George

George_George23-Aug-07 20:27