[libc-commits] [libc] [libc] mbsrtowcs implementation (PR #145791)
via libc-commits
libc-commits at lists.llvm.org
Wed Jun 25 14:47:16 PDT 2025
https://github.com/sribee8 created https://github.com/llvm/llvm-project/pull/145791
Implemented mbsrtowcs and tests for the function.
>From bf0440f29858562d200e5a3e00f66b0bf1e3d464 Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Tue, 24 Jun 2025 22:05:49 +0000
Subject: [PATCH 1/2] finished most of the implementation except for mbstate
checking
---
libc/config/linux/x86_64/entrypoints.txt | 1 +
libc/include/wchar.yaml | 9 ++
libc/src/__support/wchar/CMakeLists.txt | 16 ++++
libc/src/__support/wchar/mbsrtowcs.cpp | 44 +++++++++
libc/src/__support/wchar/mbsrtowcs.h | 29 ++++++
libc/src/wchar/CMakeLists.txt | 18 ++++
libc/src/wchar/mbsrtowcs.cpp | 41 +++++++++
libc/src/wchar/mbsrtowcs.h | 24 +++++
libc/test/src/wchar/CMakeLists.txt | 14 +++
libc/test/src/wchar/mbsrtowcs_test.cpp | 111 +++++++++++++++++++++++
10 files changed, 307 insertions(+)
create mode 100644 libc/src/__support/wchar/mbsrtowcs.cpp
create mode 100644 libc/src/__support/wchar/mbsrtowcs.h
create mode 100644 libc/src/wchar/mbsrtowcs.cpp
create mode 100644 libc/src/wchar/mbsrtowcs.h
create mode 100644 libc/test/src/wchar/mbsrtowcs_test.cpp
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index c8a6d6e648af9..ee7223c930b2c 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1249,6 +1249,7 @@ if(LLVM_LIBC_FULL_BUILD)
# wchar.h entrypoints
libc.src.wchar.mbrtowc
+ libc.src.wchar.mbsrtowcs
libc.src.wchar.mbtowc
libc.src.wchar.wcrtomb
)
diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 98cb3bdaf0ac9..065713d620cf9 100644
--- a/libc/include/wchar.yaml
+++ b/libc/include/wchar.yaml
@@ -38,6 +38,15 @@ functions:
- type: const char *__restrict
- type: size_t
- type: mbstate_t *__restrict
+ - name: mbsrtowcs
+ standards:
+ - stdc
+ return_type: size_t
+ arguments:
+ - type: wchar_t *__restrict
+ - type: const char **__restrict
+ - type: size_t
+ - type: mbstate_t *__restrict
- name: mbtowc
standards:
- stdc
diff --git a/libc/src/__support/wchar/CMakeLists.txt b/libc/src/__support/wchar/CMakeLists.txt
index 6aade4ccc84a6..c5ee4475cc884 100644
--- a/libc/src/__support/wchar/CMakeLists.txt
+++ b/libc/src/__support/wchar/CMakeLists.txt
@@ -51,3 +51,19 @@ add_object_library(
.character_converter
.mbstate
)
+
+add_object_library(
+ mbsrtowcs
+ HDRS
+ mbsrtowcs.h
+ SRCS
+ mbsrtowcs.cpp
+ DEPENDS
+ libc.hdr.types.wchar_t
+ libc.hdr.types.size_t
+ libc.src.__support.common
+ libc.src.__support.error_or
+ libc.src.__support.macros.config
+ .mbstate
+ .mbrtowc
+)
diff --git a/libc/src/__support/wchar/mbsrtowcs.cpp b/libc/src/__support/wchar/mbsrtowcs.cpp
new file mode 100644
index 0000000000000..c21897d73abc4
--- /dev/null
+++ b/libc/src/__support/wchar/mbsrtowcs.cpp
@@ -0,0 +1,44 @@
+//===-- Implementation for mbsrtowcs function -------------------*- C++ -*-===//
+//
+// 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/__support/wchar/mbsrtowcs.h"
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbrtowc.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<size_t> mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
+ size_t len, mbstate *__restrict ps) {
+ size_t i = 0;
+ // Converting characters until we reach error or null terminator
+ for (; i < len; ++i, ++dst) {
+ auto check = mbrtowc(dst, *src, 4, ps);
+ // Encoding error
+ if (!check.has_value())
+ return Error(-1);
+ // Successfully encoded, check for null terminator
+ if (*dst == L'\0') {
+ *src = nullptr;
+ return i;
+ }
+ // Set src to point right after the last character converted
+ *src = *src + check.value();
+ }
+ return i;
+}
+
+} // namespace internal
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/__support/wchar/mbsrtowcs.h b/libc/src/__support/wchar/mbsrtowcs.h
new file mode 100644
index 0000000000000..5eda23fa7baad
--- /dev/null
+++ b/libc/src/__support/wchar/mbsrtowcs.h
@@ -0,0 +1,29 @@
+//===-- Implementation header for mbsrtowcs function ------------*- C++ -*-===//
+//
+// 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___SUPPORT_WCHAR_MBSRTOWCS
+#define LLVM_LIBC_SRC___SUPPORT_WCHAR_MBSRTOWCS
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<size_t> mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
+ size_t len, mbstate *__restrict ps);
+
+} // namespace internal
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_WCHAR_MBSRTOWCS
diff --git a/libc/src/wchar/CMakeLists.txt b/libc/src/wchar/CMakeLists.txt
index f390785e5817b..110d6fc9603c3 100644
--- a/libc/src/wchar/CMakeLists.txt
+++ b/libc/src/wchar/CMakeLists.txt
@@ -65,6 +65,24 @@ add_entrypoint_object(
libc.src.__support.wchar.mbstate
)
+add_entrypoint_object(
+ mbsrtowcs
+ SRCS
+ mbsrtowcs.cpp
+ HDRS
+ mbsrtowcs.h
+ DEPENDS
+ libc.hdr.types.size_t
+ libc.hdr.types.mbstate_t
+ libc.hdr.types.wchar_t
+ libc.src.__support.common
+ libc.src.__support.macros.config
+ libc.src.__support.wchar.mbsrtowcs
+ libc.src.__support.libc_errno
+ libc.src.__support.wchar.mbstate
+ libc.src.__support.macros.null_check
+)
+
add_entrypoint_object(
mbtowc
SRCS
diff --git a/libc/src/wchar/mbsrtowcs.cpp b/libc/src/wchar/mbsrtowcs.cpp
new file mode 100644
index 0000000000000..5e83f526daedc
--- /dev/null
+++ b/libc/src/wchar/mbsrtowcs.cpp
@@ -0,0 +1,41 @@
+//===-- Implementation of mbsrtowcs ---------------------------------------===//
+//
+// 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/mbsrtowcs.h"
+
+#include "hdr/types/mbstate_t.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/macros/null_check.h"
+#include "src/__support/wchar/mbsrtowcs.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, mbsrtowcs,
+ (wchar_t *__restrict dst, const char **__restrict src,
+ size_t len, mbstate_t *__restrict ps)) {
+ LIBC_CRASH_ON_NULLPTR(src);
+ static internal::mbstate internal_mbstate;
+ wchar_t temp[len];
+ auto ret = internal::mbsrtowcs(
+ dst == nullptr ? temp : dst, src, len,
+ ps == nullptr ? &internal_mbstate
+ : reinterpret_cast<internal::mbstate *>(ps));
+ if (!ret.has_value()) {
+ // Encoding failure
+ libc_errno = EILSEQ;
+ return -1;
+ }
+ return ret.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/wchar/mbsrtowcs.h b/libc/src/wchar/mbsrtowcs.h
new file mode 100644
index 0000000000000..f8d4cc26e63ae
--- /dev/null
+++ b/libc/src/wchar/mbsrtowcs.h
@@ -0,0 +1,24 @@
+//===-- Implementation header for mbsrtowcs -------------------------------===//
+//
+// 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_MBSRTOWCS_H
+#define LLVM_LIBC_SRC_WCHAR_MBSRTOWCS_H
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
+ size_t len, mbstate_t *__restrict ps);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_MBSRTOWCS_H
diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index 48688b3bdd1f3..131e3cc13ed94 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/libc/test/src/wchar/CMakeLists.txt
@@ -37,6 +37,20 @@ add_libc_test(
libc.hdr.types.wchar_t
)
+add_libc_test(
+ mbsrtowcs_test
+ SUITE
+ libc_wchar_unittests
+ SRCS
+ mbsrtowcs_test.cpp
+ DEPENDS
+ libc.src.__support.libc_errno
+ libc.src.string.memset
+ libc.src.wchar.mbsrtowcs
+ libc.hdr.types.mbstate_t
+ libc.hdr.types.wchar_t
+)
+
add_libc_test(
mbtowc_test
SUITE
diff --git a/libc/test/src/wchar/mbsrtowcs_test.cpp b/libc/test/src/wchar/mbsrtowcs_test.cpp
new file mode 100644
index 0000000000000..c20ab570464bd
--- /dev/null
+++ b/libc/test/src/wchar/mbsrtowcs_test.cpp
@@ -0,0 +1,111 @@
+//===-- Unittests for mbsrtowcs -------------------------------------------===//
+//
+// 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 "hdr/types/wchar_t.h"
+#include "src/__support/libc_errno.h"
+#include "src/string/memset.h"
+#include "src/wchar/mbsrtowcs.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcMBSRToWCSTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcMBSRToWCSTest, OneByteOneCharacter) {
+ mbstate_t *mb;
+ LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
+ const char *ch = "A";
+ wchar_t dest[2];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &ch, 2, mb);
+ ASSERT_TRUE(dest[0] == L'A');
+ ASSERT_TRUE(dest[1] == L'\0');
+ // Should not count null terminator in number
+ ASSERT_EQ(static_cast<int>(n), 1);
+ // Should set ch to nullptr after reading null terminator
+ ASSERT_EQ(ch, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, MultiByteOneCharacter) {
+ const char *src = "\xf0\x9f\x98\xb9"; // laughing cat emoji 😹
+ wchar_t dest[2];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 2, nullptr);
+ ASSERT_EQ(static_cast<int>(dest[0]), 128569);
+ ASSERT_TRUE(dest[1] == L'\0');
+ // Should not count null terminator in number
+ ASSERT_EQ(static_cast<int>(n), 1);
+ // Should set ch to nullptr after reading null terminator
+ ASSERT_EQ(src, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, MultiByteTwoCharacters) {
+ // Two laughing cat emojis "😹😹"
+ const char *src = "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+ wchar_t dest[3];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+ ASSERT_EQ(static_cast<int>(dest[0]), 128569);
+ ASSERT_EQ(static_cast<int>(dest[1]), 128569);
+ ASSERT_TRUE(dest[2] == L'\0');
+ // Should not count null terminator in number
+ ASSERT_EQ(static_cast<int>(n), 2);
+ // Should set ch to nullptr after reading null terminator
+ ASSERT_EQ(src, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, ReadLessThanStringLength) {
+ // Four laughing cat emojis "😹😹😹😹"
+ const char *src =
+ "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+ const char *check = src;
+ wchar_t dest[3];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+ // Should have read 3 emojis
+ ASSERT_EQ(static_cast<int>(n), 3);
+ ASSERT_EQ(static_cast<int>(dest[0]), 128569);
+ ASSERT_EQ(static_cast<int>(dest[1]), 128569);
+ ASSERT_EQ(static_cast<int>(dest[2]), 128569);
+ // src should now point to the 4th cat emoji aka 13th byte
+ ASSERT_EQ((check + 12), src);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, InvalidFirstByte) {
+ // 0x80 is invalid first byte of mb character
+ const char *src =
+ "\x80\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+ wchar_t dest[3];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+ // Should return error and set errno
+ ASSERT_EQ(static_cast<int>(n), -1);
+ ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, InvalidMiddleByte) {
+ // The 7th byte is invalid for a 4 byte character
+ const char *src =
+ "\xf0\x9f\x98\xb9\xf0\x9f\xf0\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+ wchar_t dest[3];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 5, nullptr);
+ // Should return error and set errno
+ ASSERT_EQ(static_cast<int>(n), -1);
+ ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, NullDestination) {
+ // Four laughing cat emojis "😹😹😹😹"
+ const char *src =
+ "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(nullptr, &src, 5, nullptr);
+ // Null destination should still return correct number of read chars
+ ASSERT_EQ(static_cast<int>(n), 4);
+}
+
+#if defined(LIBC_ADD_NULL_CHECKS) && !defined(LIBC_HAS_SANITIZER)
+TEST_F(LlvmLibcMBSRToWCSTest, NullSource) {
+ // Passing in a nullptr source should crash the program
+ EXPECT_DEATH([] { LIBC_NAMESPACE::mbsrtowcs(nullptr, nullptr, 1, nullptr); },
+ WITH_SIGNAL(-1));
+}
+#endif // LIBC_HAS_ADDRESS_SANITIZER
>From 6f08d753e6d1518e889ae40dbbc28374086f2313 Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Wed, 25 Jun 2025 21:46:25 +0000
Subject: [PATCH 2/2] [libc] mbsrtowcs implementation
Implemented mbsrtowcs and tests for the function.
---
libc/src/__support/wchar/mbsrtowcs.cpp | 4 ++--
libc/src/wchar/mbsrtowcs.cpp | 2 +-
libc/test/src/wchar/mbsrtowcs_test.cpp | 21 +++++++++++++++++++++
3 files changed, 24 insertions(+), 3 deletions(-)
diff --git a/libc/src/__support/wchar/mbsrtowcs.cpp b/libc/src/__support/wchar/mbsrtowcs.cpp
index c21897d73abc4..4edda2bed6e44 100644
--- a/libc/src/__support/wchar/mbsrtowcs.cpp
+++ b/libc/src/__support/wchar/mbsrtowcs.cpp
@@ -25,9 +25,9 @@ ErrorOr<size_t> mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
// Converting characters until we reach error or null terminator
for (; i < len; ++i, ++dst) {
auto check = mbrtowc(dst, *src, 4, ps);
- // Encoding error
+ // Encoding error/invalid mbstate
if (!check.has_value())
- return Error(-1);
+ return Error(check.error());
// Successfully encoded, check for null terminator
if (*dst == L'\0') {
*src = nullptr;
diff --git a/libc/src/wchar/mbsrtowcs.cpp b/libc/src/wchar/mbsrtowcs.cpp
index 5e83f526daedc..a7e534f4b57c2 100644
--- a/libc/src/wchar/mbsrtowcs.cpp
+++ b/libc/src/wchar/mbsrtowcs.cpp
@@ -32,7 +32,7 @@ LLVM_LIBC_FUNCTION(size_t, mbsrtowcs,
: reinterpret_cast<internal::mbstate *>(ps));
if (!ret.has_value()) {
// Encoding failure
- libc_errno = EILSEQ;
+ libc_errno = ret.error();
return -1;
}
return ret.value();
diff --git a/libc/test/src/wchar/mbsrtowcs_test.cpp b/libc/test/src/wchar/mbsrtowcs_test.cpp
index c20ab570464bd..3fec3e76d3f68 100644
--- a/libc/test/src/wchar/mbsrtowcs_test.cpp
+++ b/libc/test/src/wchar/mbsrtowcs_test.cpp
@@ -8,6 +8,7 @@
#include "hdr/types/wchar_t.h"
#include "src/__support/libc_errno.h"
+#include "src/__support/wchar/mbstate.h"
#include "src/string/memset.h"
#include "src/wchar/mbsrtowcs.h"
#include "test/UnitTest/ErrnoCheckingTest.h"
@@ -21,6 +22,7 @@ TEST_F(LlvmLibcMBSRToWCSTest, OneByteOneCharacter) {
const char *ch = "A";
wchar_t dest[2];
size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &ch, 2, mb);
+ ASSERT_ERRNO_SUCCESS();
ASSERT_TRUE(dest[0] == L'A');
ASSERT_TRUE(dest[1] == L'\0');
// Should not count null terminator in number
@@ -33,6 +35,7 @@ TEST_F(LlvmLibcMBSRToWCSTest, MultiByteOneCharacter) {
const char *src = "\xf0\x9f\x98\xb9"; // laughing cat emoji 😹
wchar_t dest[2];
size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 2, nullptr);
+ ASSERT_ERRNO_SUCCESS();
ASSERT_EQ(static_cast<int>(dest[0]), 128569);
ASSERT_TRUE(dest[1] == L'\0');
// Should not count null terminator in number
@@ -46,6 +49,7 @@ TEST_F(LlvmLibcMBSRToWCSTest, MultiByteTwoCharacters) {
const char *src = "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
wchar_t dest[3];
size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+ ASSERT_ERRNO_SUCCESS();
ASSERT_EQ(static_cast<int>(dest[0]), 128569);
ASSERT_EQ(static_cast<int>(dest[1]), 128569);
ASSERT_TRUE(dest[2] == L'\0');
@@ -62,6 +66,7 @@ TEST_F(LlvmLibcMBSRToWCSTest, ReadLessThanStringLength) {
const char *check = src;
wchar_t dest[3];
size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+ ASSERT_ERRNO_SUCCESS();
// Should have read 3 emojis
ASSERT_EQ(static_cast<int>(n), 3);
ASSERT_EQ(static_cast<int>(dest[0]), 128569);
@@ -98,10 +103,26 @@ TEST_F(LlvmLibcMBSRToWCSTest, NullDestination) {
const char *src =
"\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
size_t n = LIBC_NAMESPACE::mbsrtowcs(nullptr, &src, 5, nullptr);
+ ASSERT_ERRNO_SUCCESS();
// Null destination should still return correct number of read chars
ASSERT_EQ(static_cast<int>(n), 4);
}
+TEST_F(LlvmLibcMBSRToWCSTest, InvalidMBState) {
+ mbstate_t *mb;
+ LIBC_NAMESPACE::internal::mbstate inv;
+ inv.total_bytes = 6;
+ mb = reinterpret_cast<mbstate_t *>(&inv);
+ // Four laughing cat emojis "😹😹😹😹"
+ const char *src =
+ "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+ wchar_t dest[3];
+ size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, mb);
+ // Should fail from invalid mbstate
+ ASSERT_EQ(static_cast<int>(n), -1);
+ ASSERT_ERRNO_EQ(EINVAL);
+}
+
#if defined(LIBC_ADD_NULL_CHECKS) && !defined(LIBC_HAS_SANITIZER)
TEST_F(LlvmLibcMBSRToWCSTest, NullSource) {
// Passing in a nullptr source should crash the program
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