static globals

[cs1975]

Hi Everyone,

I wanted to make a global variable
double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Since static keywords makes globals to file specific during
compilation.

Any help regarding this issue will be helpful.

Warm regards,
Chandra-

[santosh]

cs****@gmail.com wrote:

Hi Everyone,

I wanted to make a global variable
double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Yes. Only const disallows modification.

Since static keywords makes globals to file specific during
compilation.

If you need to access the array from another file, don't declare it with
static. Define it as an unqualified global in exactly one file and access
it from other files after including an extern declaration.

[Jim Langston]

<cs****@gmail.comwrote in message
news:11********************@z24g2000prh.googlegrou ps.com...

Hi Everyone,

I wanted to make a global variable
double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Since static keywords makes globals to file specific during
compilation.

Any help regarding this issue will be helpful.

static applied to a variable has different meanings depending on where it's
used.

static applied to a global variable states that the variable is local to the
translation unit (it also has internal linkage).

Basically that means that this global variable will only be used in this
translation unit (object file) and not needed by other object files. It
says nothing about the constantness of the variable. So, yes, you could
change rowCols in the translation unit. I believe static used in this
method is used primarily to prevent name collisions. It is common practice
when changing a #define to a variable to declare it as
static const

Without the const, however, it is a global variable to that translation unit
that can be modified like any other variable.

I have not experimented with it, but I would think it could be used for a
function declaration as well to avoid name colisions if you have the same
function declared in two different translation units (don't quote me on
that, I may be wrong).

[Chris Torek]

In article <11********************@z24g2000prh.googlegroups.c om>
<cs****@gmail.comwrote:

>I wanted to [change] a global variable

The phrase "global variable" is not defined by the C standard (and
I think not by the C++ standard either), and "means" different things
to different people. So any answer you get to the question the
answer-er thought you asked here may not be the answer to the
question *you* thought you asked.

>double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

I am updating this global variable in one of the methods in the flow,

If you are using a C++ "method", you have left C behind, and should
restrict yourself to comp.lang.c++. The rules for scopes are
subtly different in C++ than in C, and since "global" may refer
to scope (rather than linkage), any answer you get in comp.lang.c
may not be the answer to the question you thought you asked.
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) [phone]
email: forget about it http://web.torek.net/torek/index.html
Reading email is like searching for food in the garbage, thanks to spammers.

[Old Wolf]

On Aug 24, 12:57 am, [e-mail] wrote:

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Since static keywords makes globals to file specific during
compilation.

'static' means that the identifier 'rowCols' is not visible
outside of that file. However, the memory itself can still
be modified by other parts of that program, it's just that
the other part of the program cannot look up the name 'rowCols'.

[Old Wolf]

On Aug 24, 8:48 am, Chris Torek <[e-mail]:

<[e-mail]:

I am updating this global variable in one of the methods in the flow,

If you are using a C++ "method", you have left C behind,

C++ does not have methods any more than C does.
Class member functions are called 'member functions'.

People seem to call functions of either type 'methods'.

[Keith Thompson]

Old Wolf <ol*****@inspire.net.nzwrites:

On Aug 24, 8:48 am, Chris Torek <[e-mail]:

><[e-mail]:

>I am updating this global variable in one of the methods in the flow,

If you are using a C++ "method", you have left C behind,

C++ does not have methods any more than C does.
Class member functions are called 'member functions'.

People seem to call functions of either type 'methods'.

<OT>
The C++ standard uses the word "method" only in its normal English
sense, but Stroustrups book _The C++ Programming Language_ says

A virtual member function is sometimes called a _method_.

so it's probably not entriely unreasonable to talk about "methods" in
C++.
</OT>

I marked the above OT because I'm reading and posting in comp.lang.c.
If you want to discuss whether C++ has "methods", please drop the
comp.lang.c cross-post. Thanks.

But C certainly doesn't have "methods" in the sense used by some
object-oriented languages (you can implement OO in C, and you might
talk about OO methods in that context, but that's unusual).

I'm more confused about what the OP meant by "in the flow".

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[pete]

cs****@gmail.com wrote:

>
Hi Everyone,

I wanted to make a global variable
double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

As far as I can tell from your post,
you don't know why you want to make your global static.

Why do you want to make your global static?

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Since static keywords makes globals to file specific during
compilation.

--
pete

[cs1975]

On Aug 24, 2:32 am, pete <[e-mail]:

[e-mail] wrote:

Hi Everyone,

I wanted to make a global variable
double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

As far as I can tell from your post,
you don't know why you want to make your global static.

Why do you want to make your global static?

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Since static keywords makes globals to file specific during
compilation.

--
pete

Hi Pete,
I get a linker warning LNK4006 with MicroSoft CL compiler, whic is
"symbol already defined in object; second definition ignored"

Wanted to remove this warning from compilation.

regard,
chandra-

[Jim Langston]

<cs****@gmail.comwrote in message
news:11*********************@r23g2000prd.googlegro ups.com...

On Aug 24, 2:32 am, pete <[e-mail]:

>[e-mail] wrote:

Hi Everyone,

I wanted to make a global variable
double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

to static global

static double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

As far as I can tell from your post,
you don't know why you want to make your global static.

Why do you want to make your global static?

I am updating this global variable in one of the methods in the flow,

Is it really possible to change after making this variable to
static ??

Since static keywords makes globals to file specific during
compilation.

--
pete

Hi Pete,
I get a linker warning LNK4006 with MicroSoft CL compiler, whic is
"symbol already defined in object; second definition ignored"

Wanted to remove this warning from compilation.

If you want to change this variable in a function/method and you use the
static keyword, then you will have two different instances of the variable,
with different values. Probably not what you want.

So, how to get it so that both object files point to the same variable and
don't give you a compilation warning error? That is where extern comes in.

In your header file you would use:

extern double rowCols[3][3];

Having this in more that one compilation unit is fine. In fact, having it
multiple times in the same compilation unit should produce no
warnings/errors.

Then, in a .cpp file (pick one) you would do:

double rowCols[3][3] = {{1,0,0},{0,1,0},{1,0,0}};

Now, there is only one instance of rowCols, but every compilation unit that
includes the header with the extern will point to the same one.

extern means, basically, I'm going to to have a variable named rowCols[3][3]
but I"m not defining it here, it's defined in another compilation unit, when
you link, link to the same one.

Now, when a method/function changes the value of the variables, since there
is only one instance of the variable, all compilation units will "see" the
change.

[Richard Bos]

cs****@gmail.com wrote:

I get a linker warning LNK4006 with MicroSoft CL compiler, whic is
"symbol already defined in object; second definition ignored"

Wanted to remove this warning from compilation.

That warning is trivially removed by, surprise, _not defining the symbol
twice_. Not by buggering about with globals and statics.

Richard

[Barry Schwarz]

On Fri, 24 Aug 2007 01:47:30 -0700, cs****@gmail.com wrote:

>On Aug 24, 2:32 am, pete <[e-mail]:

snip

>As far as I can tell from your post,
you don't know why you want to make your global static.

Why do you want to make your global static?

snip

>I get a linker warning LNK4006 with MicroSoft CL compiler, whic is
"symbol already defined in object; second definition ignored"

Wanted to remove this warning from compilation.

You have, at the very least, a coding error in your program. It could
a design error, which is usually worse. While changing the object to
static may eliminate the diagnostic, it does nothing for the
underlying problem. All you have done is masked a symptom.
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