C / C++ / MFC Discussion Boards

Re: declaring a global variable

David Crow26-Jun-06 9:20

David Crow

26-Jun-06 9:20

TheinstruTara wrote:
That is why I am trying to make it global, so that I do not have to declare it again and again.

Why? What's wrong with a variable being declared when it is needed? You're not saving anything by using a global variable instead. That way of thinking has not been relevant with Windows in a number of years.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Re: declaring a global variable

Tara1426-Jun-06 10:19

Tara14

26-Jun-06 10:19

Well..I am not trying to save anything.
I have to type CString sql; everytime I have to use it. I guess just a bit lazy... Blush | :O

And if there is a better way of doing it, then why not!

I do know that if a variable can be declared as totally global. Just wasn't sure how.

I guess, we all try to find easier way of doing things.Some toothbrush company has come out with, 'automated toothbrush' Laugh | :laugh:

Batery operated stuff...

Fortitudine Vinsinues!

Re: declaring a global variable

Anilkumar K V26-Jun-06 18:22

Anilkumar K V

26-Jun-06 18:22

Automated Tooth brush is alreay there...But there is no available medicine for lazyness till now...

Look here.
http://www.pricegrabber.com/search_attrib.php/page_id=796/popup1%255B%255D=20:1765/

Pls dont ask for a stuff which have food for u Poke tongue | ;-P

Re: declaring a global variable

Zac Howland26-Jun-06 9:29

Zac Howland

26-Jun-06 9:29

While you can use the extern solution provided, a better solution for you would be to define that string in your string table and declare a CString object to use it when needed.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: declaring a global variable

Jun Du26-Jun-06 9:25

Jun Du

26-Jun-06 9:25

TheinstruTara wrote:
then I have to declare it again as extern CString sqla in payroll.cpp (another dialog class)?

Keyword "extern" indicates that this variable has been declared elsewhere in the same module and tells the compiler to use that declaration.

TheinstruTara wrote:
If you want to use CString sqla in all the functions of that particular .cpp file, you declare it in the header file.

That may be what you have been doing, but it's not right. You don't declare varaibles in a header, you only put macros, constants, type definitions (that sort of things) there.

In essense, header is about definition not declaration. People include your header because they want to use your type definitions, not the variables in your module!

Hope this is clearer.

Best,
Jun

Re: declaring a global variable

Tara1426-Jun-06 9:44

Tara14

26-Jun-06 9:44

But then, suppose I want to access a value (say some
double area = 3.14*m_Edit_r*m_Edit_r))
calculated in one dialog box class's .cpp file from another dialog box or just another class then how is it done.

What I usually do is declare double area in Dialog1.h, do the calulation somewhere in Dialog1.cpp
Then, in Dialog2.cpp I access it this way pDlg->area + somethng ... where pDlg is a CDialog1 object;

So i have been doing it wrong?

Fortitudine Vinsinues!

Re: declaring a global variable

Zac Howland26-Jun-06 9:54

Zac Howland

26-Jun-06 9:54

TheinstruTara wrote:
So i have been doing it wrong?

Aside from declaring the data member public, no, you did it right. Those variables should be private and be given accessor methods, though.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: declaring a global variable

Jun Du26-Jun-06 10:20

Jun Du

26-Jun-06 10:20

As per classes, the header defines a class, which in truns encapsulates some data as members. You're not declaring data in the header directly; the header still only contains type definition, which is class in this case.

TheinstruTara wrote:
Then, in Dialog2.cpp I access it this way pDlg->area + somethng ... where pDlg is a CDialog1 object;

So i have been doing it wrong?

No. This actually explains the class definition well. Your Dialog2 accesses "area" through the 1st Dialog object "pDlg", which is most likely declared as a member of Dialog2 in your header.

Best,
Jun

Re: declaring a global variable

Tara1426-Jun-06 10:26

Tara14

26-Jun-06 10:26

Thanks.

In conclusion, if I am making a module, I must not do it the same way as I do it for classes. But for simple class, I can declare variables in the header.

Fortitudine Vinsinues!

Re: declaring a global variable

David Crow26-Jun-06 9:49

David Crow

26-Jun-06 9:49

Jun Du wrote:
In essense, header is about definition not declaration.

Header (.h) files contain declarations, while source (.cpp) files contain definitions. Declarations can be seen multiple times by the compiler, while definitions can only be seen once by the compiler. A definition is also a declaration, but a declaration is not also a definition.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Re: declaring a global variable

Jun Du26-Jun-06 10:27

Jun Du

26-Jun-06 10:27

DavidCrow wrote:
Header (.h) files contain declarations, while source (.cpp) files contain definitions.

I have a feeling that the source file (.cpp) contains class implementation, not definition. The header contains the definition.

Best,
Jun

Re: declaring a global variable

David Crow26-Jun-06 10:48

David Crow

26-Jun-06 10:48

Jun Du wrote:
I have a feeling that the source file (.cpp) contains class implementation, not definition. The header contains the definition.

For creating your own class, yes, but the scope of this thread was limited to using an existing object.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Re: declaring a global variable

Michael Dunn26-Jun-06 9:43

Michael Dunn

26-Jun-06 9:43

In your stdafx.h, write:
extern CString sql;

Then in one (and only one) .cpp file, put this at global scope:
CString sql;

--Mike--
Visual C++ MVP Cool | :cool:

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VB > soccer

Re: declaring a global variable

Tara1426-Jun-06 10:27

Tara14

26-Jun-06 10:27

Thank you. That is what I was looking for.

Fortitudine Vinsinues!

Pointers...

#hackC++26-Jun-06 8:04

#hackC++

26-Jun-06 8:04

I've looked and looked, but i can't seem to find any good articles on pointers....

its all so confusing to me....

I would appriecate if anyone could point (he he) me to a good article or something you read that you though was good on pointers and references..

It would help a lot thanks...

"C++ will solve any problem."

Re: Pointers...

Jun Du26-Jun-06 8:14

Jun Du

26-Jun-06 8:14

What level do you want the literature to be technically, beginner or more advanced?

Best,
Jun

Re: Pointers...

#hackC++26-Jun-06 8:17

#hackC++

26-Jun-06 8:17

If you could find both...both,

but beginner for starters would help....

"C++ will solve any problem."

Re: Pointers...

Jun Du26-Jun-06 8:36

Jun Du

26-Jun-06 8:36

Ok, a beginner's first: this CP article.
Search CP for "pointers" and you'll get tone of articles and code snippets.

Best,
Jun

Re: Pointers...

Roland Pibinger26-Jun-06 8:17

Roland Pibinger

26-Jun-06 8:17

A TUTORIAL ON POINTERS AND ARRAYS IN C[^]

Re: Pointers...

#hackC++26-Jun-06 8:20

#hackC++

26-Jun-06 8:20

Thanks!

"C++ will solve any problem."

Re: Pointers...

Zac Howland26-Jun-06 9:04

Zac Howland

26-Jun-06 9:04

You can also check out (and I recommend reading anyway), "The C++ Programming Language", "Effective C++", "Effective STL", and "Exceptional C++". While they all cover far more topics than just pointers, they will give you a good start to learning the language as a whole.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Pointers...

David Crow26-Jun-06 9:11

David Crow

26-Jun-06 9:11

#hackC++ wrote:
I've looked and looked, but i can't seem to find any good articles on pointers....

http://c-faq.com/ptrs/index.html[^]

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Detecting a seperate app displaying a messagebox

Dan Neely26-Jun-06 7:33

Dan Neely

26-Jun-06 7:33

Is there a way to detect when a 3rd party application displays a messagebox?

Re: Detecting a seperate app displaying a messagebox

FarPointer26-Jun-06 7:39

FarPointer

26-Jun-06 7:39

Write a system wide hook for WH_CBT or something of your choice go through hooks .

Regards,
FarPointer
Blog:FARPOINTER

Re: Detecting a seperate app displaying a messagebox

David Crow26-Jun-06 9:13

David Crow

26-Jun-06 9:13

Probably not, as a message box is nothing but a dialog (#32770 class). Any application can have one of those displayed.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

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