Question

Help me out, gurus

/*
 * In this function, I want the static variable position to point to next element
 * of the str, every time I call this function.
 */
void function(char *str){

   static char *position = str;

   /* Do something here to this position */

   position += 1;
 }

The purpose of this program is to do string substitution, every time I substituted a pattern of the str I have to let the static position variable point to a new position of the str, and then I will copy every thing into another new string.

The problem is, the compiler keep telling me “the initializer element is not a constant”, how can I fix this?

Answer 1

You can’t have a static variable in your function to point to the next element of str, because position is a global variable that is initialized once, and str may have different value every time you call a function.

What you need here is a loop that iterates over str,

void func1(char *str) {
    char *p;
    for (p = str; /* some condition here */; ++p) {
        /* Do something here to this position */
    }
}

or have a loop outside this function and pass str incremented by 1 every iteration.

void func1(char *str) {
    /* Do something here to this position */
}

void func2() {
    char *str = ...;
    ...
    char *p;
    for (p = str; /* some condition here */; ++p) {
        func1(p);
    }
}

Of course, you can initialize a static to NULL first and use it to check if you started iterating over str, but that’s poor style: too stateful and error prone, not reentrant and not thread-safe.