Only canonicalise if there is room, and add docs

We could increment SIZE to ensure there would be room, but that would
disadvantage people using kstrings for binary data in power-of-2-sized
blocks.  Instead document that SIZE=KS.l+1 will ensure NUL-termination.

This fixes a bug in the previous version when the l<m invariant does not
hold (kputc_()/etc and manual manipulation only maintain the weaker l<=m);
hattip Rob Davies.

diff --git a/kstring.h b/kstring.h
index 4c803b81560daa5d3b549d768c60641f8f14fd46..360a5987a77fb7099a964dcb17b8f262a64dee4f 100644 (file)
--- a/kstring.h
+++ b/kstring.h
@@ -78,6 +78,9 @@ extern "C" {
 }
 #endif
 
+/* Ensures that the string has space for at least SIZE bytes, and ensures that
+ * it is NUL-terminated if there is room.  Thus ks_resize(&s,s.l+1) can be used
+ * to make sure that a kstring_t is both allocated and NUL-terminated.  */
 static inline int ks_resize(kstring_t *s, size_t size)
 {
        if (s->m < size) {
@@ -89,7 +92,7 @@ static inline int ks_resize(kstring_t *s, size_t size)
                else
                        return -1;
        }
-       s->s[s->l] = '\0';
+       if (s->l < s->m) s->s[s->l] = '\0';
        return 0;
 }