Is returning a pointer to a static local variable safe?

Question

I\'m working with some code that widely uses the idiom of returning a pointer to a static local variable. eg:

char* const GetString()
{
  static char sTest[         


        

Answer 1

It is very useful, as you can use the function directly as printf parameter. But, as it was mentioned, multiple calls to the function inside a single call will cause a problem, because the function uses the same storage and calling it twice will overwrite the returned string. But I tested this piece of code and it seems to work - you can safety call a function, where givemestring is used at most MAX_CALLS times and it will behave correctly.

#define MAX_CALLS 3
#define MAX_LEN 30

char *givemestring(int num)
{
        static char buf[MAX_CALLS][MAX_LEN];
        static int rotate=0;

        rotate++;
        rotate%=sizeof(buf)/sizeof(buf[0]);

        sprintf(buf[rotate],"%d",num);
        return buf[rotate];

}

The only issue is thread-safety, but this can be solved with thread local variables (gcc's __thread keyword)