CODEWITHSUNDEEP
cvariablesmemorystatickeyword
VoidWalker
VoidWalker

Reputation: 65

Is it correct to call a static variable local?

It is known that the C language supports two kinds of memory allocation through the variables in C programs:

1) Static allocation is what happens when you declare a static variable. Each static variable defines one block of space, of a fixed size. The space is allocated once, when your program is started, and is never freed.

2) Automatic allocation happens when you declare an automatic variable, such as a function argument or a local variable. The space for an automatic variable is allocated when the compound statement containing the declaration is entered, and is freed when that compound statement is exited.

(this is a full quote from http://www.cs.utah.edu/dept/old/texinfo/glibc-manual-0.02/library_3.html)

The question is: is it correct to call a static variable in a function "local" in terms of memory allocation and why? Thanks to everyone in advance.

P.S. any quotes from the C standard are welcome.

Upvotes: 3

Views: 230

Answers (5)

Barath Ravikumar
Barath Ravikumar

Reputation: 5836

The question is: is it correct to call a static variable in a function "local" in terms of memory allocation and why?

Static variables are stored in the data section of the memory allocated to the program. Even though if the scope of a static variable ends , it can still be accessed outside its scope , this may indicate that , the contents of data segment , may be independent of scope.

Example

#include <stdio.h>

int increment(void);

int main()
{
printf("\ni = %d",increment());
printf("\ni = %d",increment());
printf("\ni = %d",increment());
}

int increment(void)
{
static int i = 1;
return i++ ;
}

In the above example , after each function call to increment() , the static variable i inside the function goes out of scope every time the function returns but persistently retains its value. This is only possible because the variable is not on the same same stack as the function , but it is present entirely in a different memory area , the data segment.

Upvotes: 1

Blagovest Buyukliev
Blagovest Buyukliev

Reputation: 43558

In the context of variables, the term local most often denotes visibility and scope rather than the storage mechanism and lifetime.

Using the term local variables in C is in fact inaccurate as the standard never talks about that.

Informally, a static variable inside a function could be said to be local within the visible scope of the function, but not much more than that.

I would suggest against using the term local variables at all. Instead, one should talk about static variables within a function, automatic variables, static variables in the file scope and globals.

Upvotes: 2

md5
md5

Reputation: 23727

C standard doesn't define the term of local variable. Automatic and static refer to storage duration.

C11 (n1570), § 6.2.4 Storage durations of objects

An object has a storage duration that determines its lifetime.

Upvotes: 4

bash.d
bash.d

Reputation: 13217

There are two types of static variables in C.

  1. The global static variables, where the static states that these variables can only be seen in this translation-unit.

  2. Static variables with a local scop (i.e. in function). These are initialized once and keep their value event after going out of scope.

And to you question: no, a variable can't be static and automatic at the same time. If you check their addresses, you will se that the static variable does not live on the current stack frame.

Upvotes: 2

John Zwinck
John Zwinck

Reputation: 249582

You could call it a "function-local static variable" or something like that, but if you simply call it a "local variable" you may find that people are surprised when they find out it's actually static, and therefore has some of the properties of a global variable.

Upvotes: 3

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