Page 29 - Programming Microcontrollers in C

14 Chapter 1 Introduction to C

Inside of a function, the following declaration is made:

static int keep = 1;
When the program is loaded and executed, the value 1 is assigned
to keep. Thereafter, each time the function is entered, keep will
not be initialized but will retain the value assigned to it the last time
the function was executed.
Global variables can be designated as static. A global vari­
able that is static is similar to a conventional global variable with
the exception that it can be accessed only from the file in which it is
declared.
If there is an external variable that is declared in one file that is to
be accessed by a function defined in another file, the function must
notify the compiler that the variable is external with the use of the
keyword extern. The following is an example of such an access.
In file 1:

int able;

int main(void)
{
long quickstart(void);
long r;
.
.
.
able=17;
l=quickstart();
.
.
}

In file 2:

long quickstart(void)
{
extern int able;
.
/* do something with able */
.