What does "static" mean in C?

Question

I've seen the word static used in different places in C code; is this like a static function/class in C# (where the implementation is shared across objects)?

Pesce

Related: Static (keyword) @ Wikipedia – Pentaprism

What is the reason to remove "in a C program" from the end of the title, @Lundin? It is slightly redundant in the presence of tag c, but it lets me see the categorization more quickly, without inspecting the tags. This redundance is very comfortable when I reach the question from a direction that may contain questions about other languages, too, e.g. static or Google search. – Pentaprism

@Lundin I prefer to keep "C" in the title, because SO only appends one tag to the title (the most common?). What if some day "syntax" reaches more questions than C (since it is a cross language thing)? I'd rather use the explicit behavior :-) Edit: ah but there is a meta question saying otherwise: meta.stackexchange.com/questions/19190/… – Melly

This is an explanation I found on Quora. Definitely worth reading! – Orazio

Storage duration of static is until the program ends, instead of until the scope ends. – Goodfornothing

Related: What is a “static” function in C? – Endoblast

@CiroSantilliOurBigBook.com It now does say "syntax - What does...." – Bergh

Answer 1

1. A static variable inside a function keeps its value between invocations.
2. A static global variable or a function is "seen" only in the file it's declared in

(1) is the more foreign topic if you're a newbie, so here's an example:

#include <stdio.h>

void foo()
{
    int a = 10;
    static int sa = 10;

    a += 5;
    sa += 5;

    printf("a = %d, sa = %d\n", a, sa);
}


int main()
{
    int i;

    for (i = 0; i < 10; ++i)
        foo();
}

This prints:

a = 15, sa = 15
a = 15, sa = 20
a = 15, sa = 25
a = 15, sa = 30
a = 15, sa = 35
a = 15, sa = 40
a = 15, sa = 45
a = 15, sa = 50
a = 15, sa = 55
a = 15, sa = 60

This is useful for cases where a function needs to keep some state between invocations, and you don't want to use global variables. Beware, however, this feature should be used very sparingly - it makes your code not thread-safe and harder to understand.

(2) Is used widely as an "access control" feature. If you have a .c file implementing some functionality, it usually exposes only a few "public" functions to users. The rest of its functions should be made static, so that the user won't be able to access them. This is encapsulation, a good practice.

Quoting Wikipedia:

In the C programming language, static is used with global variables and functions to set their scope to the containing file. In local variables, static is used to store the variable in the statically allocated memory instead of the automatically allocated memory. While the language does not dictate the implementation of either type of memory, statically allocated memory is typically reserved in data segment of the program at compile time, while the automatically allocated memory is normally implemented as a transient call stack.

And to answer your second question, it's not like in C#.

In C++, however, static is also used to define class attributes (shared between all objects of the same class) and methods. In C there are no classes, so this feature is irrelevant.

Carabao

Pax, the OP doesn't know about static, so you suggest plunging him into the difference between compilation units and files ? :-) – Carabao

A compilation unit is a single file the compiler sees. Your .c file may include other .c files, but after the preprocessor sorting out the includes, the compiler eventually sees just a single "compilation unit". – Carabao

David, if you're new to C, this issue shouldn't bother you at all. It doesn't bother 99.9% of C programmers anyway. – Carabao

so if you define a static in one header file that you include into a file, but in that file define the same static another time, it is an error, because the two definitions appear in the same translation unit. – Fidel

This has got me thinking. Does the compilation unit consist of only its *.c file. For example, if I have a file called foo.c and a header called foo.h. Would the 2 of them consist of 1 compilation unit? Or would the foo.c be one complete compilation unit without the foo.h? – Cottrell

@robUK: the compiler doesn't even know about the .h files - these are combined into the .c files in the pre-processor. So yes you can say that the .c file, with all the headers included into it, are a single compilation unit. – Carabao

So does "static function" and "private function" means the same thing ? Similarly are "static global variables" and "private global variables" the same thing ? – Litmus

@user1599964: there's no concept of "private" in C, per se. However, when functions and variables are made static in a C file, they are essentially private to this C file since they can't be accessed directly from other C files. – Carabao

I appreciate you're trying to clarify things, but your notion of compilers versus pre-processors is dated and confusing... modern "compilers" (as the word is generally used) internalise the preprocessor. It's accurate and simple enough to describe a translation or compilation unit as typically consisting of one .c implementation file and whatever headers it directly or indirectly #includes, and not bring preprocessor/compiler into it at all. – Newbold

@TonyD maybe it is confusing, but it is how the compilation works. It may typically be one .c and bunch of header files, but the devil is always in what is not typical. – Pushkin

@peterph: then that can be addressed by saying "a translation unit consists of the source file(s) specified to the compiler on the command line, with each #include (direct or indirect) expanded in place". My point remains that describing "translation unit" adequately is less misleading or confusing than making statements like "A compilation unit is a single file the compiler sees." when there's not necessarily any single amalgamated "file" (on the disk, or even in the compiler's memory for that matter) involved. "static ... is "seen" only in the file it's declared in" - also misleading. – Newbold

@TonyD Sorry, but you're wrong. Preprocessing and compilation are totally different steps, and it's crucial to know how they differ. – Oakum

@MilesRout: Even sorrier that you're wrong about me being wrong - I agree with the rest of what you've said, but it doesn't relate to or contradict what I've said. Eli: "the compiler doesn't even know about the .h files - these are combined into the .c files in the pre-processor.", then me "modern "compilers" (as the word is generally used) internalise the preprocessor". I've talked about compiler not compilation. – Newbold

@TonyD The compiler does compilation. The preprocessor does preprocessing. Calling the toolchain 'the compiler' doesn't change what it is or what it does. – Oakum

Regarding the static function part, there is a good Q&A already: static function in C – Pentaprism

Might a functional definition to translation unit simply be the single .c file and all its direct/indirect includes which altogether produce a single .o file? – Organ

Why the same keyword is used in different senses? Once for storage type and other for limiting variable scope. They could not get other keywords!! C is unnecessarily made complex to understand by newbies. – Spokesman

The two cases (1) and (2) are actually the same. It doesn't matter whether the "static int sa=10;" is "inside the function" or "outside the function". The compiled program is exactly the same regardless... – Octonary

@Octonary Wrong. For (1) sa is "seen" only inside the foo() function, whereas for (2) sa can be seen directly from main() or any other function in the same .c file. – Luddite

In the example given it doesn't matter. compile it both ways and see for yourself. – Octonary

As someone who has never used static in anything other than OO fashion, this helped me understand the use of state in Perl too – Cosy

So when someone declares a global variable as static does that mean it can only be read by the file itself? Or do other files within the same directory also have access? – Carri

@paxdiablo If you were truly pedantic, you would refer to it as translation unit ;) – Oram

@Pentaprism Nope, your mentioned question has been posted years after this question. – Bombsight

IMHO the term "static global" is completely misplaced. A variable or function can't be local to a specific file and global (visible throughout the whole program) at the same time. We say "static global" because we mean a variable declared at global scope (outside of any function) inside a file, but technically it isn't real global. It is lets call it "regional" to keep the difference to "local" in the manner of function-local. – Endoblast

Because of this ambiguity there is much confusion brought to people who come newly to C. One good example is a recent question, where the OP used the term "static global" and confused him/herself as well as the answerers, here. You can get a short overview in the comments to that question. – Endoblast

@EliBendersky Since your answer is viewed by many new C programmers I would highly suggest you to replace the term "static global". It is ambiguous, formally incorrect and confuses people. – Endoblast

The Wikipedia terminology is crap^Wwrong and should be removed. static does not "set scope" (scope is determined by the placement of a declaration inside or outside blocks). static sets the linkage of an identifier to internal linkage which means identifiers from other translation units cannot refer to it. This makes it possible to have a different object with the same name in another source file. – Facsimile

Fun trivia about why these two unrelated usages of static (storage duration, and linkage) got the same name. When the second one was introduced (I don't remember which one came first, probably the storage duration), the implementers of the new feature wanted old compilers to still be able to compile newer code. Introducing a new keyword (intern would have been wonderful) would have confused older compiler versions, and so they reused a keyword that existed. Globals already had the program long storage duration, so it became static for internal linkage as well. – Podolsk

So its like it only declares the static variables one and then subsequent calls of the function ignore its redefinition and use the value it was assigned on the original call, meanwhile it is also being incremented. It's keeping the variable within scope outside the scope of the function. – Banebrudge

Answer 2

There is one more use not covered here, and that is as part of an array type declaration as an argument to a function:

int someFunction(char arg[static 10])
{
    ...
}

In this context, this specifies that arguments passed to this function must be an array of type char with at least 10 elements in it. For more info see my question here.

Foldaway

I didn't think C had array arguments? Linus Torvalds rants angrily about people doing this. – Chairborne

@jamieb: C doesn't have array arguments, but this specific syntax means that the function expects arg[0] through to arg[9] to have values (which also implies that the function does not accept a null pointer). Compilers could utilise this information somehow for optimisation, and static analysers can utilise this information to ensure that the function is never given a null pointer (or if it can tell, an array with fewer elements than specified). – Foldaway

@Qix -- This was a new overloaded meaning given to static in C99. It is more than a decade and a half old, but not all compiler writers have embraced all of C99 features -- so C99 as a whole largely remains unknown. – Richma

@Chairborne I'm not 100% sure what you mean by "array arguments", but if you mean int arr[n];, then that is a VLA (variable-length array), which was added in C99. Is that what you meant? – Robi

Does it mean, I can not pass any char* to this function, because nobody knows if it could be incremented by 10 ... I doubt your answer, although its interesting. – Shantae

Answer 3

Short answer ... it depends.

1. Static defined local variables do not lose their value between function calls. In other words they are global variables, but scoped to the local function they are defined in.

2. Static global variables are not visible outside of the C file they are defined in.

3. Static functions are not visible outside of the C file they are defined in.

Tamar

So does "static function" and "private function" means the same thing ? Similarly are "static global variables" and "private global variables" the same thing ? – Litmus

This is about C. There is no private/public in C. – Arrogance

@Litmus although there is no private in C, your analogy is good: static makes things "private" to a given file. And files in C often map to classes in C++. – Melly

Answer 4

Multi-file variable scope example

Here I illustrate how static affects the scope of function definitions across multiple files.

a.c

#include <stdio.h>

/*
Undefined behavior: already defined in main.
Binutils 2.24 gives an error and refuses to link.
https://mcmap.net/q/17190/-why-does-borland-compile-with-multiple-definitions-of-same-object-in-different-c-files-while-gcc-does-not
*/
/*int i = 0;*/

/* Works in GCC as an extension: https://mcmap.net/q/17191/-why-uninitialized-global-variable-is-weak-symbol */
/*int i;*/

/* OK: extern. Will use the one in main. */
extern int i;

/* OK: only visible to this file. */
static int si = 0;

void a() {
    i++;
    si++;
    puts("a()");
    printf("i = %d\n", i);
    printf("si = %d\n", si);
    puts("");
}

main.c

#include <stdio.h>

int i = 0;
static int si = 0;

void a();    

void m() {
    i++;
    si++;
    puts("m()");
    printf("i = %d\n", i);
    printf("si = %d\n", si);
    puts("");
}

int main() {
    m();
    m();
    a();
    a();
    return 0;
}

GitHub upstream.

Compile and run:

gcc -c a.c -o a.o
gcc -c main.c -o main.o
gcc -o main main.o a.o

Output:

m()
i = 1
si = 1

m()
i = 2
si = 2

a()
i = 3
si = 1

a()
i = 4
si = 2

Interpretation

• there are two separate variables for si, one for each file
• there is a single shared variable for i

As usual, the smaller the scope, the better, so always declare variables static if you can.

In C programming, files are often used to represent "classes", and static variables represent private static members of the class.

What standards say about it

C99 N1256 draft 6.7.1 "Storage-class specifiers" says that static is a "storage-class specifier".

6.2.2/3 "Linkages of identifiers" says static implies internal linkage:

If the declaration of a file scope identifier for an object or a function contains the storage-class specifier static, the identifier has internal linkage.

and 6.2.2/2 says that internal linkage behaves like in our example:

In the set of translation units and libraries that constitutes an entire program, each declaration of a particular identifier with external linkage denotes the same object or function. Within one translation unit, each declaration of an identifier with internal linkage denotes the same object or function.

where "translation unit is a source file after preprocessing.

How GCC implements it for ELF (Linux)?

With the STB_LOCAL binding.

If we compile:

int i = 0;
static int si = 0;

and disassemble the symbol table with:

readelf -s main.o

the output contains:

Num:    Value          Size Type    Bind   Vis      Ndx Name
  5: 0000000000000004     4 OBJECT  LOCAL  DEFAULT    4 si
 10: 0000000000000000     4 OBJECT  GLOBAL DEFAULT    4 i

so the binding is the only significant difference between them. Value is just their offset into the .bss section, so we expect it to differ.

STB_LOCAL is documented on the ELF spec at http://www.sco.com/developers/gabi/2003-12-17/ch4.symtab.html:

STB_LOCAL Local symbols are not visible outside the object file containing their definition. Local symbols of the same name may exist in multiple files without interfering with each other

which makes it a perfect choice to represent static.

Variables without static are STB_GLOBAL, and the spec says:

When the link editor combines several relocatable object files, it does not allow multiple definitions of STB_GLOBAL symbols with the same name.

which is coherent with the link errors on multiple non static definitions.

If we crank up the optimization with -O3, the si symbol is removed entirely from the symbol table: it cannot be used from outside anyways. TODO why keep static variables on the symbol table at all when there is no optimization? Can they be used for anything? Maybe for debugging.

See also

• analogous for static functions: https://mcmap.net/q/17187/-what-is-a-quot-static-quot-function-in-c
• compare static with extern, which does "the opposite": How do I use extern to share variables between source files?

C++ anonymous namespaces

In C++, you might want to use anonymous namespaces instead of static, which achieves a similar effect, but further hides type definitions: Unnamed/anonymous namespaces vs. static functions

Melly

Answer 5

It depends:

int foo()
{
   static int x;
   return ++x;
}

The function would return 1, 2, 3, etc. --- the variable is not on the stack.

a.c:

static int foo()
{
}

It means that this function has scope only in this file. So a.c and b.c can have different foo()s, and foo is not exposed to shared objects. So if you defined foo in a.c you couldn't access it from b.c or from any other places.

In most C libraries all "private" functions are static and most "public" are not.

Sykes

+1 for mentioning x not on stack or heap. It's on the static memory space. – Enfield

@Gob00st static memory space? you meant "Data Segment"...? – Pforzheim

@YoushaAleayoub See this and this. – Fitzger

In most C libraries all "private" functions are static and most "public" are not. Hello I have a question about this, you said most , I wonder how can static functions behave as public – Snowshed

@Sekomer • if a static function pointer "escapes" as a function pointer return value of another function, or by being set as a function pointer via member variable in a struct. – Cabob

Answer 6

People keep saying that 'static' in C has two meanings. I offer an alternate way of viewing it that gives it a single meaning:

• Applying 'static' to an item forces that item to have two properties: (a) It is not visible outside the current scope; (b) It is persistent.

The reason it seems to have two meanings is that, in C, every item to which 'static' may be applied already has one of these two properties, so it seems as if that particular usage only involves the other.

For example, consider variables. Variables declared outside of functions already have persistence (in the data segment), so applying 'static' can only make them not visible outside the current scope (compilation unit). Contrariwise, variables declared inside of functions already have non-visibility outside the current scope (function), so applying 'static' can only make them persistent.

Applying 'static' to functions is just like applying it to global variables - code is necessarily persistent (at least within the language), so only visibility can be altered.

NOTE: These comments only apply to C. In C++, applying 'static' to class methods is truly giving the keyword a different meaning. Similarly for the C99 array-argument extension.

Balneal

Your (a) is redundant at best. No variable whatsoever is visible outside its scope. That's simply the definition of scope. What you mean is called linkage in the C Standard. static gives internal linkage to an identifier. – Facsimile

Answer 7

static means different things in different contexts.

1. You can declare a static variable in a C function. This variable is only visible in the function however it behaves like a global in that it is only initialized once and it retains its value. In this example, everytime you call foo() it will print an increasing number. The static variable is initialized only once.

   void foo ()
   {
   static int i = 0;
   printf("%d", i); i++
   }
   

2. Another use of static is when you implement a function or global variable in a .c file but don't want its symbol to be visible outside of the .obj generated by the file. e.g.

   static void foo() { ... }
   

Ambitious

Answer 8

From Wikipedia:

In the C programming language, static is used with global variables and functions to set their scope to the containing file. In local variables, static is used to store the variable in the statically allocated memory instead of the automatically allocated memory. While the language does not dictate the implementation of either type of memory, statically allocated memory is typically reserved in data segment of the program at compile time, while the automatically allocated memory is normally implemented as a transient call stack.

Stacte

Wikipedia at its worst. Static sets linkage, not scope. Understanding the difference is crucial. – Facsimile

@Facsimile No one asking a question about static will know what linkage means. However, the concept of scope is common to practically all languages, so anyone should be able to roughly understand how static affects objects based on this description. For the same reason, it mentions "the containing file" rather than "the current compilation unit". – Bodwell

@Bodwell Linkage is not scope. static does not set scope. Even "the containing file" is wrong, since scope only starts at the end of a declarator, not at the beginning of a file. The Wikipedia entry as quoted is so misleading, it would make Trump blush. – Facsimile

@Facsimile It doesn't really matter though, at all. For all intents and purposes, static makes global variables local to the file and removes them from the truly global scope. There's no point flexing fancy terms when a simple question expecting a simple, straight-forward answer is asked. Sure, it's not exactly correct, but it helps everyone understand the general idea and that's more important than some terminology nuances. – Bodwell

Answer 9

If you declare a variable in a function static, its value will not be stored on the function call stack and will still be available when you call the function again.

If you declare a global variable static, its scope will be restricted to within the file in which you declared it. This is slightly safer than a regular global which can be read and modified throughout your entire program.

Pappas

Answer 10

I hate to answer an old question, but I don't think anybody has mentioned how K&R explain it in section A4.1 of "The C Programming Language".

In short, the word static is used with two meanings:

1. Static is one of the two storage classes (the other being automatic). A static object keeps its value between invocations. The objects declared outside all blocks are always static and cannot be made automatic.
2. But, when the static keyword (big emphasis on it being used in code as a keyword) is used with a declaration, it gives that object internal linkage so it can only be used within that translation unit. But if the keyword is used in a function, it changes the storage class of the object (the object would only be visible within that function anyway). The opposite of static is the extern keyword, which gives an object external linkage.

Peter Van Der Linden gives these two meanings in "Expert C Programming":

• Inside a function, retains its value between calls.
• At the function level, visible only in this file.

Dustcloth

There's a third storage class, register. Some people also make the case for a fourth storage class, allocated, for the storage returned by malloc and friends. – Facsimile

@Facsimile 'register' is only a hint to the compiler; register storage cannot be enforced from within the C source. So I wouldn't consider it a storage class. – Nino

@Nino I'm afraid the ISO C Standard disagrees with your view, as it clearly makes register a storage-class specifier (C99 6.7.1 Storage-class specifiers). And it is more than just a hint, for example you can't apply the address-of operator & on an object with storage class register regardless of whether the compiler allocates a register or not. – Facsimile

@Facsimile Thanks for reminding me about &. I might have done too much C++.....Anyhow, while 'register' is a storage-class specifier, in reality the compiler will likely create the same machine code for the (useless) 'auto' specifier as for the 'register' specifier. So the only thing remaining is the source-code level restriction of not being able to take an address. BTW, this little discussion led me to find a bug in Netbeans; since my latest update, it defaults to the g++ tool chain on new C projects! – Nino

Answer 11

Share what I learned about this point.

In C static is a declaration specifier, which falls into three categories:

• storage classes: there are four classes: auto, static, extern and register.
• type qualifiers: like keywords: const, volatile, etc.
• type specifiers: like keywords: void, char, short, int, etc.

So static is a storage classes. It will determine the following three properties of each variable in a C program.

• storage duration: means when memory is allocated for the variable and when the memory is released. A variable with static storage duration stays at the same memory location as long as the program is running.
• scope: means the portion of the program text in which the variable can be accessed. A static variable has a file scope instead of a block scope.
• linkage: means the extent to which the variable can be shared by different parts(or files) of a program. If a static variable is declared inside a block then it has no linkage. If a static variable is declared outside blocks, then it has internal linkage. Internal linkage makes it accessible in a single file.

The static storage class has a different effect on a variable depending on it is declared outside a block or inside a block. Need to consider case by case.

Hephaestus

Answer 12

A static variable is a special variable that you can use in a function, and it saves the data between calls, and it does not delete it between calls. For example:

void func(void) {
    static int count; // If you don't declare its value, it is initialized with zero
    printf("%d, ", count);
    ++count;
}

int main(void) {
    while(true) {
        func();
    }
    return 0;
}

The output:

0, 1, 2, 3, 4, 5, ...

Paver

Answer 13

In C, static has two meanings, depending on scope of its use. In the global scope, when an object is declared at the file level, it means that that object is only visible within that file.

At any other scope it declares an object that will retain its value between the different times that the particular scope is entered. For example, if an int is delcared within a procedure:

void procedure(void)
{
   static int i = 0;

   i++;
}

the value of 'i' is initialized to zero on the first call to the procedure, and the value is retained each subsequent time the procedure is called. if 'i' were printed it would output a sequence of 0, 1, 2, 3, ...

Discomfit

Answer 14

If you declare this in a mytest.c file:

static int my_variable;

Then this variable can only be seen from this file. The variable cannot be exported anywhere else.

If you declare inside a function the value of the variable will keep its value each time the function is called.

A static function cannot be exported from outside the file. So in a *.c file, you are hiding the functions and the variables if you declare them static.

Cottrell

Answer 15

It is important to note that static variables in functions get initialized at the first entry into that function and persist even after their call has been finished; in case of recursive functions the static variable gets initialized only once and persists as well over all recursive calls and even after the call of the function has been finished.

If the variable has been created outside a function, it means that the programmer is only able to use the variable in the source-file the variable has been declared.

Simsar

Answer 16

Static variables in C have the lifetime of the program.

If defined in a function, they have local scope, i.e. they can be accessed only inside those functions. The value of static variables is preserved between function calls.

For example:

void function()
{
    static int var = 1;
    var++;
    printf("%d", var);
}

int main()
{
    function(); // Call 1
    function(); // Call 2
}

In the above program, var is stored in the data segment. Its lifetime is the whole C program.

After function call 1, var becomes 2. After function call 2, var becomes 3.

The value of var is not destroyed between functions calls.

If var had between non static and local variable, it would be stored in the stack segment in the C program. Since the stack frame of the function is destroyed after the function returns, the value of var is also destroyed.

Initialized static variables are stored in the data segment of the C program whereas uninitialized ones are stored in the BSS segment.

Another information about static: If a variable is global and static, it has the life time of the C program, but it has file scope. It is visible only in that file.

To try this:

file1.c

static int x;

int main()
{
    printf("Accessing in same file%d", x):
}

file2.c

    extern int x;
    func()
    {
        printf("accessing in different file %d",x); // Not allowed, x has the file scope of file1.c
    }

run gcc -c file1.c

gcc -c file2.c

Now try to link them using:

gcc -o output file1.o file2.o

It would give a linker error as x has the file scope of file1.c and the linker would not be able to resolve the reference to variable x used in file2.c.

References:

1. http://en.wikipedia.org/wiki/Translation_unit_(programming)
2. http://en.wikipedia.org/wiki/Call_stack

Yerkovich

I understand that the data is persistent, meaning that it won't be lost after each function call, but why doesn't static int var = 1; change the value back to one each time – Falda

Answer 17

A static variable value persists between different function calls andits scope is limited to the local block a static var always initializes with value 0

Beowulf

Answer 18

There are 2 cases:

(1) Local variables declared static: Allocated in data segment instead of stack. Its value retains when you call the function again.

(2) Global variables or functions declared static: Invisible outside compilation unit (i.e. are local symbols in symbol table during linking).

Credulity

Answer 19

The scope of static variables is limited to the file in which they are declared. This applies to static functions as well.

The scope of static variables declared in a function is different however. It is limited to the function, like non-static variables, but it retains its value across multiple calls to that function.

Osteomyelitis

Answer 20

Static variables have a property of preserving their value even after they are out of their scope!Hence, static variables preserve their previous value in their previous scope and are not initialized again in the new scope.

Look at this for example - A static int variable remains in memory while the program is running. A normal or auto variable is destroyed when a function call where the variable was declared is over.

#include<stdio.h> 
int fun() 
{ 
  static int count = 0; 
  count++; 
  return count; 
} 

int main() 
{ 
  printf("%d ", fun()); 
  printf("%d ", fun()); 
  return 0; 
}

This will output: 1 2

As 1 stays in the memory as it was declared static

Static variables (like global variables) are initialized as 0 if not initialized explicitly. For example in the below program, value of x is printed as 0, while value of y is something garbage. See this for more details.

#include <stdio.h> 
int main() 
{ 
    static int x; 
    int y; 
    printf("%d \n %d", x, y); 
}

This will output : 0 [some_garbage_value]

These are the major ones I found that weren't explained above for a newbie!

Eliga

Answer 21

In C programming, static is a reserved keyword which controls both lifetime as well as visibility. If we declare a variable as static inside a function then it will only visible throughout that function. In this usage, this static variable's lifetime will start when a function call and it will destroy after the execution of that function. you can see the following example:

#include<stdio.h> 
int counterFunction() 
{ 
  static int count = 0; 
  count++; 
  return count; 
} 

int main() 
{ 
  printf("First Counter Output = %d\n", counterFunction()); 
  printf("Second Counter Output = %d ", counterFunction()); 
  return 0; 
}

Above program will give us this Output:

First Counter Output = 1 
Second Counter Output = 1 

Because as soon as we call the function it will initialize the count = 0. And while we execute the counterFunction it will destroy the count variable.

Fibrinolysin

>Above program will give us this Output: First Counter Output = 1 Second Counter Output = 1 < Not true. Static variables get initialized only once. So the output will be 1, then 2, and so on. – Nino

Global and Static variables are initialized to 0, You shouldn't re-assign them to zero in every function call. – Snowshed