1 files changed, 122 insertions, 0 deletions
diff --git a/tests/test-strncpy.c b/tests/test-strncpy.c
new file mode 100644
index 00000000..847e55f8
--- /dev/null
+++ b/tests/test-strncpy.c
@@ -0,0 +1,122 @@
+/* Test of strncpy() function.
+   Copyright (C) 2010-2026 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <string.h>
+
+#include <stddef.h>
+
+#include "zerosize-ptr.h"
+#include "macros.h"
+
+/* Test the library, not the compiler+library.  */
+static char *
+lib_strncpy (char *s1, char const *s2, size_t n)
+{
+  return strncpy (s1, s2, n);
+}
+static char *(*volatile volatile_strncpy) (char *, char const *, size_t)
+  = lib_strncpy;
+#undef strncpy
+#define strncpy volatile_strncpy
+
+#define MAGIC (char)0xBA
+
+static void
+check_single (const char *input, size_t length, size_t n)
+{
+  char *dest;
+  char *result;
+
+  dest = (char *) malloc (1 + n + 1);
+  ASSERT (dest != NULL);
+
+  for (size_t i = 0; i < 1 + n + 1; i++)
+    dest[i] = MAGIC;
+
+  result = strncpy (dest + 1, input, n);
+  ASSERT (result == dest + 1);
+
+  ASSERT (dest[0] == MAGIC);
+  {
+    size_t i;
+    for (i = 0; i < (n <= length ? n : length + 1); i++)
+      ASSERT (dest[1 + i] == input[i]);
+    for (; i < n; i++)
+      ASSERT (dest[1 + i] == 0);
+  }
+  ASSERT (dest[1 + n] == MAGIC);
+
+  free (dest);
+}
+
+static void
+check (const char *input, size_t input_length)
+{
+  size_t length;
+
+  ASSERT (input_length > 0);
+  ASSERT (input[input_length - 1] == 0);
+  length = input_length - 1; /* = strlen (input) */
+
+  for (size_t n = 0; n <= 2 * length + 2; n++)
+    check_single (input, length, n);
+
+  /* Check that strncpy (D, S, N) does not look at more than
+     MIN (strlen (S) + 1, N) units.  */
+  {
+    char *page_boundary = (char *) zerosize_ptr ();
+
+    if (page_boundary != NULL)
+      {
+        for (size_t n = 0; n <= 2 * length + 2; n++)
+          {
+            size_t n_to_copy = (n <= length ? n : length + 1);
+            char *copy;
+
+            copy = (char *) page_boundary - n_to_copy;
+            for (size_t i = 0; i < n_to_copy; i++)
+              copy[i] = input[i];
+
+            check_single (copy, length, n);
+          }
+      }
+  }
+}
+
+int
+main (void)
+{
+  /* Simple string.  */
+  { /* "Grüß Gott." */
+    static const char input[] = "Gr\303\274\303\237 Gott.";
+    check (input, SIZEOF (input));
+  }
+
+  /* Test zero-length operations on NULL pointers, allowed by
+     <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3322.pdf>.  */
+
+  ASSERT (strncpy (NULL, "x", 0) == NULL);
+
+  {
+    char y[1];
+    ASSERT (strncpy (y, NULL, 0) == y);
+  }
+
+  return test_exit_status;
+}