[libc-commits] [libc] [libc] Add `ctime_s` (PR #110676)

[Nick Desaulniers via libc-commits]

================
@@ -0,0 +1,39 @@
+//===-- Implementation of ctime_s function --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "ctime_s.h"
+#include "hdr/errno_macros.h"
+#include "src/__support/CPP/limits.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "time_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+using LIBC_NAMESPACE::time_utils::TimeConstants;
+
+LLVM_LIBC_FUNCTION(int, ctime_s,
+                   (char *buffer, size_t buffer_size, const time_t *t_ptr)) {
+  if (t_ptr == nullptr || buffer == nullptr ||
+      *t_ptr > cpp::numeric_limits<int32_t>::max()) {
+    return EINVAL;
+  }
+
+  if (buffer_size < TimeConstants::ASCTIME_MAX_BYTES) {
+    return ERANGE;
+  }
+
+  if (time_utils::asctime(time_utils::localtime(t_ptr), buffer, buffer_size) ==
+      nullptr) {
+    return EINVAL;
+  }
----------------
nickdesaulniers wrote:

K.3.8.3.3 describes `ctime_s`:

> errno_t ctime_s(char *s, rsize_t maxsize, const time_t *timer);
 2 Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and shall not be greater
than RSIZE_MAX.
3 If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null pointer and
maxsize is not equal zero and is not greater than RSIZE_MAX.

So setting `buffer[0] = '\0'` should be handled in this PR.  Please do so, then add a test.

https://github.com/llvm/llvm-project/pull/110676