C / C++ / MFC

multiple definition of.....

28-Jan-10 23:19

There is the COleDateTimeSpan class for that, see the MSDN example: "Elapsed Time: Automation Classes".
Smile | :)

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krish_kumar28-Jan-10 22:02

krish_kumar

28-Jan-10 22:02

hii
Here I give my header file and .c file

/* main.h*/

#include <stdio.h>
#include <stdlib.h>

struct linked_list{
int data;
struct linked_list *next;
};

typedef struct linked_list node_t;

void display (void);
node_t *root = 0;
----------------------------------------------------------------------
/* display.c */

#include "./../inc/main.h"

extern node_t *root;

void display ( )
{
node_t *temp = root;
while (temp -> next != root)
printf(" %d", temp->data);
}

----------------------------------------------------------------------------
while compiling it gives this error

qs2/src/display.c:8: multiple definition of `root'
obj/create.o:/qs2/src/create.c:6: first defined here
obj/display.o: In function `display':

I think this error reltes to node_t *root = 0; ,extern node_t *root;

but I dont know how to clear it ...???

seeking help ...!!

Thnaking you

CPallini28-Jan-10 22:10

28-Jan-10 22:10

krish_kumar wrote:
node_t *root = 0;

You must NOT initialize the global variable inside the header (.h) file, change it to:

node_t *root;

Then inside just one source (.c) file (e.g. create.c) initialize it this way:

node_t *root = 0;

KingsGambit28-Jan-10 22:48

KingsGambit

28-Jan-10 22:48

If root is already declared inside the main.h file and that header is included in the display.c, then why the extern node_t *root; is declared in display.c? I think you can remove extern node_t *root; from display.c

CPallini28-Jan-10 23:05

28-Jan-10 23:05

That (probably) will not solve his problem, since (apparently) the header file is included both by display.c and create.c (incidentally this shows why you should never define a variable inside a header file).
Smile | :)

KingsGambit28-Jan-10 23:32

KingsGambit

28-Jan-10 23:32

Yes, it is better not to declare variable inside the headers.

I was pointing out, when the header is included in the c file, it become a single translation unit. So, the unit already has the variable. Then there is no extern is required.

David Crow30-Jan-10 5:30

David Crow

30-Jan-10 5:30

Rejeesh.T.S wrote:
Yes, it is better not to declare variable inside the headers.

I think you are confusing declaring with defining.

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KingsGambit31-Jan-10 17:58

KingsGambit

31-Jan-10 17:58

Thanks for correcting. I would have mentioned "defining". Smile | :)

member function confusion

Avi Berger29-Jan-10 8:07

Avi Berger

29-Jan-10 8:07

You have it backwards.

Your extern node_t *root; belongs in your .h file. It declares to anyone that includes it that there is such a variable that is created someplace and can be used.

Your node_t *root = 0; belongs in exactly one .c file and no .h file. It defines (creates) the variable. You only do this once. If you put this in a header file, than each .c file that uses that header would create a separate variable of that name. Those multiple variables of the same name which are globally visible and accessible would conflict with each other, hence the error multiple definition of `root'

tasumisra28-Jan-10 20:10

tasumisra

28-Jan-10 20:10

Hi Guys i have a member function and a variable .. while accessing member function can we have access the variable also....

vikas da

Cedric Moonen28-Jan-10 20:15

Cedric Moonen

28-Jan-10 20:15

Can you show with some sample code what you are trying to do. I really didn't get your question.

Cédric Moonen
Software developer

Charting control [v3.0]
OpenGL game tutorial in C++

CPallini28-Jan-10 21:05

28-Jan-10 21:05

tasumisra wrote:
Hi Guys i have a member function and a variable .. while accessing member function can we have access the variable also....

If you have also a C++ book, please read it. Roll eyes | :rolleyes:

On the serious side: read the f#*?in' book!
There are some rules about information hiding in C++, and what you said doesn't help us answering the question.
Smile | :)

Nelek28-Jan-10 21:59

Nelek

28-Jan-10 21:59

If you couldn't... you wouldn't be able to use Get/Set functions (a.k.a = accessing a function that access the variable)

If that is not the answer you expected, then ask something ~~a bit~~ quite more concrete

Regards.
--------
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CPallini28-Jan-10 22:05

28-Jan-10 22:05

Nelek wrote:
f that is not the answer you expected, then ask something a bit quite more concrete

May I have a Beer | [beer]

sir (plz plz urgenz)? Big Grin | :-D

Nelek28-Jan-10 22:22

Nelek

28-Jan-10 22:22

Yes of course you may have it, but not drink it Poke tongue | ;-P

drinking is not allowed at job Roll eyes | :rolleyes:

Regards.
--------
M.D.V. Wink | ;)

CPallini28-Jan-10 22:28

28-Jan-10 22:28

Nelek wrote:
drinking is not allowed at job

Nah, they allow me drinking here. They know, when drunk, I'm more productive... Big Grin | :-D