C / C++ / MFC

15-Jun-06 3:31

When I declare a member static in a class, it throws a linker error stating it's an unresolved external symbol..

Error Message:

<br />
CTimp error LNK2001: unresolved external symbol "public: static char * CAvCT::m_szApplicationName" (?m_szApplicationName@CAvCT@@2PADA)<br />

When I make it non-static, it works fine. Why is that so?? Confused | :confused:

Please help.

The member is declared public. i.e :

<br />
public:<br />
static int x;<br />

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C^hris L^osinger15-Jun-06 3:34

C^hris L^osinger

15-Jun-06 3:34

you still need to define the variable:

foo.h

CFoo
{
public:
   static int blah; // somewhere, there's a variable named CFoo::blah
};

foo.cpp

#include "foo.h"

int CFoo::blah = 0; // and here it is

Eytukan15-Jun-06 3:39

15-Jun-06 3:39

Chris now a different version of it.
But is it not obvious that you are declaring it again ? in the .cpp file?

<br />
AvCT.cpp(16): error C2086: 'int CAvCT::xxx' : redefinition<br />
<br />
AvCT.cpp(16): error C2655: 'CAvCT::xxx' : definition or redeclaration illegal in current scope<br />

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Cedric Moonen15-Jun-06 3:51

Cedric Moonen

15-Jun-06 3:51

The difference between a static and a non-static variable is that the static variable will be shared among all instances of the class (so, it doesn't belong to a specific instance). Because of that, declaring it inside the class is not sufficient, you need to define it outside in the cpp file. If you try to do the same with a non-static variable, you'll get an error because declaring the variable in the class is sufficient.

Cédric Moonen
Software developer

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C^hris L^osinger15-Jun-06 3:59

C^hris L^osinger

15-Jun-06 3:59

VuNic wrote:
But is it not obvious that you are declaring it again ? in the .cpp file?

since i can't see your code, i don't know what you're doing here and can't explain the error (did you remove the "static" in your .H?).

but, static member variables require both parts: the declaration and the definition (as my first reply and all the other replies to your question show) . without the .CPP part, your variable has no space allocated for it - since it's not part of a class instance, you have to give it a place to live outside the class.

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Eytukan15-Jun-06 4:04

15-Jun-06 4:04

Got it! thanks chris!

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Viorel.15-Jun-06 3:39

Viorel.

15-Jun-06 3:39

When you declare a static data member (in *.h file), you should also implement it in the *.cpp file:

// MyClass.h file:
//
class MyClass
{
    static int x; 
};
//
// MyClass.cpp file:
//
int MyClass::x; // this line you missed

So you missed to allocate the space for your static variable. Just a declaration of static data members is not enough.

David Crow15-Jun-06 3:40

David Crow

15-Jun-06 3:40

VuNic wrote:
static int x;

Has x been initialized/defined (in the .cpp file)?

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

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

Eytukan15-Jun-06 3:45

15-Jun-06 3:45

Yes, I declared it in the .h file, and initialzed in the constructor.

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David Crow15-Jun-06 3:47

David Crow

15-Jun-06 3:47

Just because it has been declared does not mean it has been defined. Define x in the class' .cpp file. Static members are initialized outside of any class methods (e.g., file scope).

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

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

You were all right!

Eytukan15-Jun-06 4:01

15-Jun-06 4:01

First off, Sorry!, Time is running out for me , so out of panic, I wasn't quite listening to you guys completely. I should have put the definition of the static member again in the .cpp. I did it wrong doing it inside the constructor or a function. Now I put it out side the constructor. It's fine now.

<br />
#include <class.h><br />
int class::x; // ok now!<br />
void class::class()<br />
{<br />
int class::x; //sh*t! sorry.<br />
}<br />
void class::func()<br />
{<br />
<br />
}<br />

Thanks, CL, David, viorel, cederic.. and SORRY FOR THE LATE ACKNOWLEDGEMENT . Need to rush.. thanks a lot.

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color in unix/dos??

Larsson15-Jun-06 3:30

Larsson

15-Jun-06 3:30

Hello!,
I need to code a program that works in UNIX and dos there I can use text color, green, red and so on. How can I do that?

the text I need to put on the screen need to be in color.

Re: color in unix/dos??

James R. Twine15-Jun-06 3:34

James R. Twine

15-Jun-06 3:34

   Well, VT/XTerm color codes can be used to write in color to a (supported) Unix console. I would suggest using something like the curses library for that, but it has been quite some time since I did any console-coloring so some other libraries may be around.

   If you only need to run the app on Unix but access it from DOS (do you mean a Win32 Console?) and Unix, so that there is only one platform to build for, use curses and connect to it using a terminal emulator that supports ANSI/XCode color codes.

   If you need to build for Unix and Windows, I would suggest that you use the Console Functions in Win32 to do coloring in the Windows/Console build.

   Peace!

-=- James

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Re: color in unix/dos??

Eytukan15-Jun-06 3:35

15-Jun-06 3:35

hey that's a cool work to do.. settextcolor() Smile | :)

If remember it correctly. I dont know about UNIX though. And I'm talking about Borland C++ complier.

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Re: color in unix/dos??

Eytukan15-Jun-06 3:44

15-Jun-06 3:44

In VC :

SetConsoleTextAttribute ( m_hConsole,<br />
                              FOREGROUND_RED |<br />
                                FOREGROUND_GREEN |<br />
                                FOREGROUND_BLUE );

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Hex in Edit

Try15-Jun-06 3:12

Try

15-Jun-06 3:12

Hi All,

How to enter only Hexadecimal values in EditBox in Dialog?

Thanks in Advance.

David Crow15-Jun-06 3:22

David Crow

15-Jun-06 3:22

Use a masked-edit control. There are several to choose from here at CP. If that is too elaborate for you, derive your own class from CEdit(), and override the OnChar() method. In that method, only allow 0-9 and A-F characters.

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

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

Eytukan15-Jun-06 3:25

15-Jun-06 3:25

Handle the WM_CHAR and allow only 0-9 + A-F + 'x' .

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toxcct13-Sep-06 1:56

toxcct

13-Sep-06 1:56

no backspace allowed ?

he will be surprised Roll eyes | :rolleyes:

TOXCCT >>> GEII power

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Eytukan13-Sep-06 2:03

13-Sep-06 2:03

WOW! You live in history? just like Van Helsing? oh man this thread is too old!! Laugh | :laugh:

by the way I'm like Google, don't like "deleting" :-> Poke tongue | ;-P

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Link2006 wrote:Let's take it outside of CP
Jeremy : Please don't.I would love to see this.I'm making the popcorn already.

toxcct13-Sep-06 2:06

toxcct

13-Sep-06 2:06

VuNic wrote:
You live in history?

nope, just browsing the forum, searching for a topic, instead than asking for a question that has been asked soooo many times already Wink | ;)

TOXCCT >>> GEII power

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