what does "static" mean in C

Answer 1

I'm not a C programmer, but if static in C means anythign like it does in other languages I use then STATIC STRUC... means that the structure is common amongst all instances of this class.

Say I had a class variable called Z. Usual behaviour is that the value of this variable is specific to a particular instance of a classs, but when it is static, all instances of the class share the same value of Z at all times.

I don't know how this applies to C, isnt C object-less?

Answer 2

static tells that a function or data element is only known within the scope of the current compile.

In addition, if you use the static keyword with a variable that is local to a function, it allows the last value of the variable to be preserved between successive calls to that function.

So if you say:

static struct ...

in a source file no other source files could use the struct type. Not even with an extern declaration. But if you say:

struct ...

then other source files could access it via an extern declaration.

Answer 3

Outside a function, static makes whatever it's applied to have file scope. For example:

int a_function(int x) { ... }

This function will have global linkage, and can be accessed by any other object file. You just have to declare it to use it, as is usually done in a header file:

int a_function(int x);

However, if you use static in the definition, then the function is visible only to the source file where it is defined:

static int a_function(int x) { ... }

In that case, other object files can't access this function. The same applies to variables:

static int x;

This makes x a global variable, visible only within it's source file. A "static struct" by itself doesn't do anything, but consider this syntax:

struct {
    int x;
    int y;
} p1, p2;

This declares two global variables (p1 and p2), each of an "anonymous" struct type. If you append static:

static struct {
    int x;
    int y;
} p1, p2;

Then static applies to p1 and p2, making them visible only within their source file.