access static variables in different files

Question

0.00/5 (No votes)

See more:

I have a header file a1.h which looks like this
a1.h

static int sum;
int data;

Now i am including this a1.h in two .cpp files one.cpp and two.cpp.
Questions:
1.Will both the files share the sum variable or each will have its own copy?
2.what is the difference between sum and data in terms of memory allocation when a1.h is included in both the files?
3.dont static variables have a file scope, so how is it accessible in other files?

Posted 12-Feb-12 22:26pm

Abhinay Kumar

Add a Solution

3 solutions

Solution 1

The best you can do is try and compile it, and see what happens.
Good luck,

Posted 12-Feb-12 22:37pm

Pablo Aliskevicius

Comments

Abhinay Kumar 13-Feb-12 4:53am

This a silly answer.I came here after compiling these programs.

CPallini 13-Feb-12 5:36am

After a question like yours, there's no silly answer.

Pablo Aliskevicius 14-Feb-12 2:06am

Dear Abhinay,
Based on your question, I assume that you are new to C/C++. First and foremost, welcome on board!
Second, since you're on CodeProject since 2008, I assume you're not new to programming. In your profile, you don't say much about yourself, so anyone trying to help you will have to guess - I guess you have a background in either .NET or Java, or possibly Visual Basic.
If this is true, I can recommend a site where you can read about C++, you can find there a good book that is meant for programmers trying to learn C++ after knowing another language: http://www.mindviewinc.com/Books/downloads.html, the book names are "Thinking in C++, 2nd edition, Volume 1" and "Thinking in C++, Volume 2: Practical Programming". I have recommended those books to colleages coming to C++ from C and from C#, and they have found them interesting.
Of course, if my guesses are wrong and you have a background in C++, you should totally ignore this post.
Again, good luck,

Solution 3

1) Each file will have its own "sum" variable, and hence memory will be allocated twice, because it is declared as static (file scope).
2) "data" has global scope hence both *.c files will compile but linker will fail with "multiply defined symbol"-type error.
3) There is no way to share static variables across files (unless you start doing something really unorthodox - e.g. you could work out the address in memory where the variable will end up - but this will be just plain bad practice). Moreover, there is no need to share static variables and/or functions as the only reason you declared them as static is to prevent global scope.
4) You should not define variables or any objects for that matter in header files. Declare them in header files and then instantiate in c files.

Posted 13-Feb-12 12:13pm

michaelmel

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

CPallini · Accepted Answer · 2012-02-12T23:09:00

Solution 2

You really shouldn't put that stuff in the header file.
That said, I guess you'll get a linker error for the data variable (multiple symbol definitions) while each source file will get its own copy of the sum variable.

Posted 12-Feb-12 23:09pm

CPallini

Updated 12-Feb-12 23:14pm

v2

Comments

Abhinay Kumar 13-Feb-12 5:16am

since i am including the file i am not getting any linking error.

CPallini 13-Feb-12 5:23am

I suppose it is your (or your compiler's) fault.
Please detail your code and report info about your build environment.
After the guess, I did a test (with VS2005), getting the link error:
'error LNK2005: "int data" (?data@@3HA) already defined in [...]'

Abhinay Kumar 13-Feb-12 7:00am

yes correct after i did it in eclipse i got the error but in turbo C++ i wasnt somehow getting the error.

Abhinay Kumar 13-Feb-12 7:15am

cant i access data in both the files using extern declaration.How to do it?

CPallini 13-Feb-12 7:58am

If you need to access the variable defined in one source file (say 'one.cpp') from another source file (say 'two.cpp') then you may:
(1) define it in one.cpp: int data;
(2) declare it as extern in two.cpp: extern int data;

Abhinay Kumar 13-Feb-12 9:04am

do i have to include one.cpp in two.cpp?

CPallini 13-Feb-12 9:04am

NOPE.