started mbstowcs implementation

Author: Sriya Pratipati

libc/src/wchar/mbstowcs.cpp

@@ -0,0 +1,29 @@
+//===-- Implementation of mbstowcs ----------------------------------------===//
+//
+// 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 "src/wchar/mbstowcs.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbstate.h"
+#include "src/__support/wchar/string_converter.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, mbstowcs,
+                   (wchar_t *__restrict pwcs, const char *__restrict s,
+                    size_t n)) {
+  static internal::mbstate internal_mbstate;
+  internal::StringConverter<char8_t> str_conv(
+      reinterpret_cast<const char8_t *>(pwcs), &internal_mbstate, n);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/wchar/mbstowcs.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for mbstowcs --------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_WCHAR_MBSTOWCS_H
+#define LLVM_LIBC_SRC_WCHAR_MBSTOWCS_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int mbstowcs(wchar_t *__restrict pwcs, const char *__restrict s, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_MBSTOWCS_H