Question

I wrote a function that that shortens a string (sentence of words) at requested length. I do not want that a the cut of the sentence happens to be in middle of a single word. So i skip back n chars until I reach a space and cut the sentence string there.
My problem is not really a problem, compiling my function spits out a warning that says “warning: value computed is not used”, see the commented line in the code. The function works as expected though.
So either I am blind, or I am sitting to long on my project, actually I do not understand that warning. Could anybody please point me the flaw in the function?

char *
str_cut(char *s, size_t len) {
    char *p = NULL;
    int n = 3;

    p = s + len;
    if (p < (s + strlen (s))) {
        /*
         * do not cut string in middle of a word.
         * if cut-point is no space, reducue string until space reached ...
         */
        if (*p != ' ')
            while (*p != ' ')
                *p--;   // TODO: triggers warning: warning: value computed is not used

        /* add space for dots and extra space, terminate string */
        p += n + 1;
        *p = '\0';

        /* append dots */
        while (n-- && (--p > s))
            *p = '.';
    }
    return s;
}

My compiler on the development machine is “gcc version 4.2.4 (Ubuntu 4.2.4-1ubuntu4)”

Answer 1

The warning is due to the * (dereference) — you aren’t using the dereferenced value anywhere. Just make it:

p--;

and the warning should go away.