local static variables

[Moore]

hi,

is it correct to state that a static variable is created only once and initialised only once and occupies some special global memory?

So lets say some sub routines declare and initialise a local static variable of the same name.

Is this possible - I mean will the variables only have local scope to the sub routines they are declared and initialised in ?
Will they exist seperately or how are they allocated?

void my_func1 ()
{
	static int var = 0;
                // do whatever
}

void my_func2 ()
{
	static int var = 0;
                // do whatever
}


int main ()
{
	my_func1();
                my_func2();
	return 0;
}

[Xatrix]

life of a static variable declared in a function begins at the time of 1st execution of the function and till the program ends. Yes it's allocated only once and contains the value which was assigned to it in that function while the program is running. In your example, these are two different variables, and they have different addresses in memory. And they are seen only in the functions they are declared in.

Hope this helps some,
Oleg

[Graham]

Just to be clear, a static local is only initialised once - when it's created. If you change its value in the function, it will retain that value on the next call.

[sunnypalsingh]

See This
http://www.cprogramming.com/tutorial/statickeyword.html

[Moore]

ok, thanks alot everyone .

[humptydumpty]

hi,

is it correct to state that a static variable is created only once and initialised only once and occupies some special global memory?

So lets say some sub routines declare and initialise a local static variable of the same name.

Is this possible - I mean will the variables only have local scope to the sub routines they are declared and initialised in ?
Will they exist seperately or how are they allocated?

 
void my_func1 ()
{
	static int var = 0;
// do whatever
}
 
void my_func2 ()
{
	static int var = 0;
// do whatever
}
 
 
int main ()
{
	my_func1();
my_func2();
	return 0;
}

as Graham and Xatrix explained you very well.in your Program u r using two static variable local to the function.
First something regarding static
In both C and C++ the keyword static has two basic meanings, which
unfortunately often step on each other’s toes:


Allocated once at a fixed address; that is, the object is created in a special
static data area rather than on the stack each time a function is called. This is
the concept of static storage.

Local to a particular translation unit (and local to a class scope in C++, as
you will see later). Here, static controls the visibility of a name, so that
name cannot be seen outside the translation unit or class. This also
describes the concept of linkage, which determines what names the linker
will see.

According to your Program==>>

When you create a local variable inside a function, the compiler allocates
storage for that variable each time the function is called by moving the stack
pointer down an appropriate amount. If there is an initializer for the variable,
the initialization is performed each time that sequence point is passed.



Sometimes, however, you want to retain a value between function calls. You
could accomplish this by making a global variable, but then that variable
would not be under the sole control of the function. C and C++ allow you to
create a static object inside a function; the storage for this object is not on the
stack but instead in the program’s static data area. This object is initialized
only once, the first time the function is called, and then retains its value
between function invocations.

[Moore]

hi,

According to your Program==>>
When you create a local variable inside a function, the compiler allocates
storage for that variable each time the function is called by moving the stack
pointer down an appropriate amount. If there is an initializer for the variable,
the initialization is performed each time that sequence point is passed.

So this is a little confusing as it states that the "initialisation is performed each time that sequence point is passed"

so considering the sample program again, are you saying that each time the my_func 's are called, that new storage is allocated and init to 0 is done again? If so how can the "var" retain its value?

thanks.

[humptydumpty]

hi,
So this is a little confusing as it states that the "initialisation is performed each time that sequence point is passed"
so considering the sample program again, are you saying that each time the my_func 's are called, that new storage is allocated and init to 0 is done again? If so how can the "var" retain its value?
thanks.

Nope In case of static variable only Singel TIme Initialization take Place .

have u read this

C and C++ allow you to create a static object inside a function; the storage for this object is not on the stack but instead in the program’s static data area. This object is initialized only once, the first time the function is called, and then retains its value between function invocations.

In Upper Quote i mean to say if this is a Auto variable

have a look on This
According to your Program==>>
When you create a local variable inside a function, the compiler allocates storage for that variable each time the function is called by moving the stack pointer down an appropriate amount. If there is an initializer for the variable, the initialization is performed each time that sequence point is passed.

[Moore]

yes and that is my understanding, but I thought that the paragragh I quoted from your previous post was a little contradictory to the highlighted red text.

regardless, I pretty much understand it now.

thanks.

[humptydumpty]

yes and that is my understanding, but I thought that the paragragh I quoted from your previous post was a little contradictory to the highlighted red text.

regardless, I pretty much understand it now.

thanks.

u welcome. and sorry to take second time to understand

[exterminator]

So lets say some sub routines declare and initialise a local static variable of the same name. Is this possible - I mean will the variables only have local scope to the sub routines they are declared and initialised in ? Will they exist seperately?

I guess that rest of your concerns have been answered. About the existence of two static variables with same name in two different functions in the same translation unit, probably there is some kind of name-mangling to ensure independent and unique existence but I am not sure about how compilers do this actually. And I would be little concerned about it since the compiler does this job for me very well. Hope this helps. Regards.

[Moore]

great, thanks again to all.