Minor improvement to substr().

2 files changed, 16 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 2759539b..7c7fbccb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2014-09-01         Arnold D. Robbins     <arnold@skeeve.com>
+
+	* builtin.c (do_substr): Return "" instead of null string in case
+	result is passed to length() with --lint. Based on discussions in
+	comp.lang.awk.
+
 2014-08-27         Arnold D. Robbins     <arnold@skeeve.com>
 
 	* configure.ac: Add test for strcasecmp.
diff --git a/builtin.c b/builtin.c
index 0995fdf7..6e4a1b72 100644
--- a/builtin.c
+++ b/builtin.c
@@ -1759,7 +1759,14 @@ do_substr(int nargs)
 			else if (do_lint == DO_LINT_INVALID && ! (d_length >= 0))
 				lintwarn(_("substr: length %g is not >= 0"), d_length);
 			DEREF(t1);
-			return dupnode(Nnull_string);
+			/*
+			 * Return explicit null string instead of doing
+			 * dupnode(Nnull_string) so that if the result
+			 * is checked with the combination of length()
+			 * and lint, no error is reported about using
+			 * an uninitialized value. Same thing later, too.
+			 */
+			return make_string("", 0);
 		}
 		if (do_lint) {
 			if (double_to_int(d_length) != d_length)
@@ -1813,7 +1820,7 @@ do_substr(int nargs)
 		if (do_lint && (do_lint == DO_LINT_ALL || ((indx | length) != 0)))
 			lintwarn(_("substr: source string is zero length"));
 		DEREF(t1);
-		return dupnode(Nnull_string);
+		return make_string("", 0);
 	}
 
 	/* get total len of input string, for following checks */
@@ -1830,7 +1837,7 @@ do_substr(int nargs)
 			lintwarn(_("substr: start index %g is past end of string"),
 				d_index);
 		DEREF(t1);
-		return dupnode(Nnull_string);
+		return make_string("", 0);
 	}
 	if (length > src_len - indx) {
 		if (do_lint)