C Language Storage Classes static
Example
The static storage class serves different purposes, depending on the location of the declaration in the file:
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To confine the identifier to that translation unit only (scope=file).
/* No other translation unit can use this variable. */ static int i; /* Same; static is attached to the function type of f, not the return type int. */ static int f(int n); -
To save data for use with the next call of a function (scope=block):
void foo() { static int a = 0; /* has static storage duration and its lifetime is the * entire execution of the program; initialized to 0 on * first function call */ int b = 0; /* b has block scope and has automatic storage duration and * only "exists" within function */ a += 10; b += 10; printf("static int a = %d, int b = %d\n", a, b); } int main(void) { int i; for (i = 0; i < 5; i++) { foo(); } return 0; }This code prints:
static int a = 10, int b = 10 static int a = 20, int b = 10 static int a = 30, int b = 10 static int a = 40, int b = 10 static int a = 50, int b = 10
Static variables retain their value even when called from multiple different threads.
C99
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Used in function parameters to denote an array is expected to have a constant minimum number of elements and a non-null parameter:
/* a is expected to have at least 512 elements. */ void printInts(int a[static 512]) { size_t i; for (i = 0; i < 512; ++i) printf("%d\n", a[i]); }The required number of items (or even a non-null pointer) is not necessarily checked by the compiler, and compilers are not required to notify you in any way if you don't have enough elements. If a programmer passes fewer than 512 elements or a null pointer, undefined behavior is the result. Since it is impossible to enforce this, extra care must be used when passing a value for that parameter to such a function.
